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Editorial BoardRichard Breuhaus, John Cashman, Michael DiDonato, Dick Elliott, Chris Finnegan, Jeff Hawk, Al John, Bob Kelley-Wickemeyer, Elizabeth Lund, Jay Maloney, Tom Melody, John Mowery, Jerome Schmelzer, William Siegele, Roger Stropes, Bill Williams

Technical Review CommitteeFrank Billand, Richard Breuhaus, Roy Bruno, John Creighton, Edward Dobkoski, Dick Elliott, Giday Girmay, Bruce Groenewegen, Al John, Warren Lamb, Bob Manelski, Tom Melody, Doug Mohl, Norm Pauk, Gary Prescott, Jerome Schmelzer, William Siegele, William Tsai, Joan Walsh, Todd Zarfos

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Boeing Model 80Chicago, April 1932, over Lake Michigan.

This trimotor had a flying range of 460 mi.

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AERO ONLINE

RICH HIGGINS The Boeing Enterprise Onemaintenance management software systemhas a modular design that optimizes majorairline support functions, improves fleet utilization, decreases maintenance costs,and better manages inventory.

NEW ETOPS REGULATIONS Regulatory changes are coming to airplane operationsbecause of a data-driven paradigm shift that has occurred since ETOPS flying began18 years ago.

737 APPROACH NAVIGATION OPTIONS A suite of new flight deck navigation options willenhance the proven approach capability of737-600/-700/-800/-900 airplanes. CategoryIIIB Autoland, Global Navigation SatelliteSystem Landing System, Integrated ApproachNavigation, and Navigation PerformanceScales improve safety and performance anddecrease operating costs.

MAINTENANCE OF HIGH-STRENGTH ALLOY STEELCOMPONENTS Airline personnel need to follow proper maintenance procedures andrework practices, checklists, and guidelinesduring the maintenance and overhaul oflanding gear and flap components made ofhigh-strength alloy steel.

Boeing 777-300ER

Issue No.22SECOND-QUARTER 2003 – APRIL Contents

22MAINTENANCE

12FLIGHT OPERATIONS

03

PERSPECTIVE 02

FLIGHT OPERATIONS

COVER

Enterprise One is an ERP tool speci-fically tailored to the air transport industry.It’s a set of integrated software modulesthat can help you optimize major supportfunctions such as maintenance planningand scheduling, engineering operations,logistics management, document manage-ment, and configuration control. EnterpriseOne allows you to improve fleet utilization,decrease maintenance costs, and manageinventory better.

The beauty of Enterprise One is that themodules are designed to integrate seam-lessly, forming a comprehensive, digitallybased management system. At the sametime, the modular design makes it easy for you to select just the portions you need to meet your specific requirements.

For example, Royal Brunei has opted to install four portions of Enterprise One:

■ Maintenance modules to streamline regu-latory compliance reporting and tailor maintenance programs for each airplane in the Royal Brunei fleet.

■ Engineering modules to track airworthiness directives and service bulletins more efficiently.

■ Logistics modules to support heavy volumes of spare parts procurement andinventory transactions.

■ The Portable Maintenance Aid,™ a documentmanagement product to help mechanics troubleshoot airplane maintenance.

The modularity of Enterprise One gives you the ability to use the softwaresystem in the best way for your particularoperation. You also have the flexibility to expand your information technology capabilities in the future.

For more information, e-mail [email protected].

We are committed to your success.

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This month marksBoeing’s official entréeinto the enterprise re-source planning (ERP)market as we begin

the installation of our Enterprise One maintenance managementsoftware system at launch customer Royal Brunei Airlines. The instal-lation also exemplifies our continued commitment to your success.

RICH HIGGINSVICE PRESIDENT

MAINTENANCE ENGINEERING AND PUBLICATIONS BOEING COMMERCIAL AVIATION SERVICES

PERSPECTIVE

AERO Second-Quarter 2003 — April

3

CHET EKSTRAND

VICE PRESIDENT

REGULATORY AFFAIRS

BOEING COMMERCIAL AIRPLANES

MOHAN PANDEY

SENIOR MANAGER

OPERATIONAL REGULATORY AFFAIRS


AEROSecond-Quarter 2003 — April

NNEEWWEETTOOPPSS RREEGGUULLAATTIIOONNSS

Extended-range operations with two-engineairplanes (ETOPS) rank among the safest and mostreliable of all flight operations. Pending rulemakingby the U.S. Federal Aviation Administration mayexpand these reliability enhancements and opera-tional protections to all extended-diversion-timeoperations (i.e., flying on routes with the potentialfor an extended diversion), not just those per-formed with two-engine airplanes.

As airplane range capabilities continue to increase, flights across remote regionsof the world are becoming more common. The global aviation community—which collaborativelydefined and proposed this U.S. rulemaking—believes that applying ETOPS rules to all extended-diversion-time operations will raise the industry toa higher and uniform standard.

F L I G H T O P E R A T I O N S

Second-Quarter 2003 — April4 AERO

n December 16, 2002,the Aviation Rulemaking

Advisory Committee (ARAC)—an advisory committee of the U.S.Federal Aviation Administration(FAA)— presented to the FAA itsfindings and recommendations onextended operations (i.e., operationson routes with the potential for an extended-duration diversion).Initiated by the FAA tasking state-ment of June 14, 2000, this pro-posed U.S. rulemaking marks theculmination of more than two yearsof global collaboration to reviewcurrent requirements for extended-range operations with two-engineairplanes (ETOPS) and proposeupdated and standardized requirements that will embrace all extended-diversion-time opera-tions, not just those performed with two-engine airplanes.

The ARAC ETOPS WorkingGroup comprised expert represen-tatives from many of the world’sairlines, airframe and enginemanufacturers, pilots’ associations,regulatory authorities, and non-governmental organizations. Inkeeping with its proposal thatthe extended-operations protectionsbe applied broadly to protect all airplanes, regardless of the numberof engines, the ETOPS WorkingGroup further recommended that the term ETOPS itself beredefined to simply mean extendedoperations. (See “ARAC ETOPSWorking Group Participants,” p. 7.)

The FAA will evaluate the proposed ARAC findings and recommendations, make whateverchanges it deems appropriate, andpublish the results in a Notice ofProposed Rulemaking (NPRM)

O for public review and comment.Following comment resolution,the FAA is expected to enact newextended-operations rules, perhapsas soon as late 2004.

This article discusses the reasons behind this global activityand describes the specific regu-latory changes that the ARAC has proposed.

THE ETOPS PARADIGM SHIFTWhen the conservative ETOPS program began in 1985, its intentwas to ensure that the safety of two-engine airplanes would matchthat of three- and four-engine air-planes on long-range transoceanicroutes. Implicit in the ETOPS ruleswas the initial assumption that turbine-powered airplanes with

■ 29,000 ETOPS flights per month■ 2,626,000 cumulative ETOPS flights■ 94 current ETOPS operators

BOEING ETOPS ROUTES THROUGH SEPTEMBER 2002

FIGURE

1

Second-Quarter 2003 — April AERO 5

ETOPS IS THE STATE OF THEART IN INTERCONTINENTAL AIR TRAVEL

ETOPS is the dominant mode oftransatlantic flight operations todayand accounts for a rapidly growingcomponent of transpacific and otheroperations as well. Since 1985, morethan 3 million ETOPS flights havebeen logged using the twinjets of several manufacturers. Today, about125 operators worldwide log an additional 1,100 ETOPS flights eachday. Of this industry total, Boeingtwinjets alone have performed morethan 2.6 million ETOPS flights, and94 Boeing operators fly nearly 1,000 more each day (fig. 1).

This vast service experience revealsthat ETOPS ranks among the safestand most reliable of all flight opera-tions. This success results from thepreclude and protect philosophy ofETOPS, which enhances flight opera-tions in two ways:■ ETOPS-related design improvements

and maintenance practices increaseairplane systems and engine relia-bility, making it less likely that an airplane will need to divert from its intended course and land at analternate airport.

■ ETOPS operational requirementsintroduce proactive measures thatprotect the airplane, passengers, andcrew should a diversion occur.

This philosophy has indirectly bene-fited the entire industry. All commer-cial operations today — includingthose performed with three- and four-engine airplanes — benefit from gainsin the reliability and robustness of airplane engines and systems initiallyachieved through ETOPS programs.

1

two engines were inherently lesssafe than those with three or moreengines. As a result, a separate setof more stringent requirements wasdeemed necessary for operatingtwo-engine airplanes on routes with the potential for an extended-duration diversion.

Since then, however, extensiveETOPS service experience has

brought about a profound revisionto that initial thinking. After nearlytwo decades of highly successfulETOPS around the world, the global aviation community todayviews ETOPS in a different light.Characterizing this profound data-driven paradigm shift are the present-day industry percep-tions that

1. ETOPS is the state of the art inintercontinental air travel.

2. Engine reliability is no longer thesingle focus of safety concerns.

3. A uniform standard is desirablefor all extended operations.

6 AERO Second-Quarter 2003 — April

Operators flying three- and four-engine airplanes are not currentlyrequired to meet the high ETOPSstandard. Nevertheless, some operatorsalready comply with key ETOPS safetyenhancements on a voluntary basis.This elective application of ETOPSbest practices suggests that the main-tenance and operational benefits ofETOPS are well recognized by theglobal industry and that operators findthem cost effective.

ENGINE RELIABILITY IS NOLONGER THE SINGLE FOCUS OFSAFETY CONCERNS

In the past, concerns about flight safetyfocused first and foremost on the re-liability of propulsion systems. Whenocean-spanning commercial flight operations began after World War II,that narrow focus was appropriate inlight of the limited reliability of pistonengines. During the 1940s and 1950s,in fact, piston engine–related eventswere the predominant cause of airlineraccidents and contributed to a world-wide fleet hull-loss accident rate thatwas some 60 times higher than today’s.

The limited reliability of pistonengines led to an operating restrictionbeing placed on two-engine airplanes50 years ago. The intent of the so-called 60-Minute Rule of 1953 (U.S. Federal Aviation Regulation[FAR] 121.161) was to bar two-enginepropeller airplanes, such as the DouglasDC-3, from flying extended routes thenmore safely served by four-enginepropeller types, such as the DC-4. Thatpiston-era operating restriction remainsin effect at the time of this writing.

During the late 1950s, however, thetransition to turbine power broughtabout a quantum leap in propulsion system reliability. Engine reliability hascontinued to improve in the jet age, somuch so that today’s high-bypass-ratiofanjet engines are at least 50 timesmore reliable than the large piston en-gines that inspired the 60-Minute Rule.

By the 1970s, advancing technologyhad set the stage for two-engine,turbine-powered airplanes to safely

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exceed the 60-min operating restriction.The result was ETOPS, which began in1985 with 120-min diversion authorityand the requirement for an averageengine in-flight shutdown (IFSD) rate ofjust 0.05 per 1,000 engine-hours. With180-min ETOPS authority, which fol-lowed in 1988, an even more stringentreliability target of just 0.02 IFSDs per1,000 engine-hours was specified.

In this way, ETOPS drove manu-facturers and operators alike to pursuedramatic gains in propulsion systemreliability. The industry met this chal-lenge and bettered it. During the pastfew years, in fact, the average IFSDrate of the worldwide 180-min ETOPS

fleet has typically been at or below0.01 IFSDs per 1,000 engine-hours —twice the reliability required for suchoperations. So profound has this trendbeen that propulsion reliabilities un-achievable just 15 years ago are todayroutine in the modern twinjet fleet.

In light of these advances, andbecause the safety and reliability oftwo-engine airplanes equal or exceedthose of three- or four-engine airplanes,the industry no longer views propul-sion system reliability as the primarysafety and reliability concern inextended operations. Instead, currentrulemaking recognizes that a varietyof airplane systems and operationalissues (e.g., cargo fire suppressioncapability, weather conditions andfacilities at alternate airports) are

relevant to overall safety and reliabilityon routes with the potential for anextended diversion.

A UNIFORM STANDARD ISDESIRABLE FOR ALL EXTENDEDOPERATIONS

All airplanes flown on extended-diversion-time routes face similar oper-ating challenges in terms of weather,terrain, and limitations in navigationand communications infrastructure.Given that the operating environment is common to all extended operations,and that all categories of jetliner aresafe, the global aviation communitybelieves a uniform standard is desirablefor extended operations. The globalcommunity further recognizes thatapplying ETOPS requirements to allairplanes — not just those with twoengines — will raise the industry to a higher and uniform standard.

Although diversions are rare, anyairplane might someday need to divertto an airport other than its intendeddestination for various reasons (e.g.,passenger illness, smoke in the flightdeck or cabin, turbulence, adversewinds, weather, fuel leak, cargo fire,in-flight engine failure or shutdown).Thus, the dual ETOPS philosophy ofprecluding diversions and protectingthe passengers, crew, and airplane onthose rare occasions when diversionsdo occur is applicable to all extendedoperations, not just those performedwith two-engine airplanes.

As a result of ETOPS, the industryhas achieved significant improvementsin the reliability and robustness of air-plane engines and systems. However,such efforts can never entirely preventdiversions because most are unrelatedto the airplane, its systems, or itsengines. In fact, fewer than 10 percentof all diversions during extended operations are airplane related, andfewer than 3 percent are the result of an in-flight engine failure or shutdown.In general, of course, engine failurestend to occur during takeoff and initialclimb rather than during the cruisephase of flight where ETOPS is flown.

3

So profound has this trend been

that propulsion reliabilities

unachievable just 15 years ago

are today routine in the modern twinjet fleet.

AERO 7Second-Quarter 2003 — April AERO

PROPOSED U.S. REGULATORY CHANGESThis paradigm shift created growingawareness around the world that the regulatory framework currently governing twinjet and other extendedoperations should be reviewed. Consequently, the FAA — which

meets its responsibility to update regulations through the proven ARACprocess — initiated the collaborativeARAC activity previously described.

The ARAC-proposed regulations(table 1) might change as a result of the current FAA review and pending

NPRM comment processes. We at The Boeing Company are proud to have participated in this globalARAC effort, which will make flyingeven safer and more reliable in thecoming years. Pages 8 through 10detail the proposed changes.

ETOPS authorization

Modify existing rule FAR 121.161 to codify ETOPS in the U.S. federal aviation regulations; describe the redefinition of ETOPS and the updated requirements being proposed for the authorization of all extended operations.

Definitions Add a new rule, FAR 121.7, to add the definitions of ETOPS-applicable terms to ensure un-derstanding of and compliance with the updated ETOPS requirements now being proposed.

Propulsion- related diversions

Issue new guidance clarifying the requirements for twinjet diversion in the event of an in-flight engine failure or shutdown; specify what factors shall and shall not be considered sufficient justification for the crew to fly beyond the nearest suitable alternate airport.

Dispatch Add a new rule specifying dispatch or flight-release requirements for weather at ETOPS alternate airports; further require that weather be updated at the start of the ETOPS phase of flight to verify the continuing availability of a valid ETOPS alternate.

Communi-cations

Add a new rule requiring voice communications, where available, and the most reliable communications technology, voice based or data link, for all extended operations beyond 180 min; require that another form of communications be available in case communication is not possible with the most reliable technology.

Modify existing rule FAR 121.415 to require training for crew members and dispatchers in their roles and responsibilities in the operator’s passenger recovery plan.

Passenger recovery plan

Modify existing rules FARs 121.135 and 121.97 to require all extended operators to develop a plan that ensures the well-being of passengers at diversion airports and provides for their safe retrieval without undue delay.

Fuel reserve Add a new rule specifying the reserve fuel to be carried to protect the airplane in the event of a cabin depressurization followed by an extended diversion at low altitude to an alternate airport.

Performance data

Modify existing rule FAR 121.135 to require all ETOPS operators to have the applicable performance data available to support their extended operations.

Cargo fire suppression

Add a new rule requiring that ETOPS diversion times shall not exceed the time limit, minus 15 min, specified in the Airplane Flight Manual for that airplane’s most time-limited system, which is typically cargo fire suppression.

Maintenance Add a new rule making ETOPS maintenance standards applicable to all airplanes flown in extended operations.

Polar operations

Modify existing rule FAR 121.161 to define polar-area zones of ETOPS applicability in which ETOPS requirements apply at all times. This requirement applies to all operations north of 78°N latitude (North Pole) and south of 60°S latitude (South Pole).

Rescue and fire fighting

Modify existing rule FAR 121.106 to require rescue and fire-fighting equipment to be available at any airport designated as an ETOPS en route alternate.

Other proposedchanges

Modify the rules governing transport-category airplane and engine design to incorporate ETOPS enhancements that reduce the rate of airplane diversions and protect airplanes when they divert.

PROPOSED ARAC RULEMAKING AND GUIDANCE

TABLE

1

AIRLINESU.S.— American Airlines, American Trans Air, Continental Airlines, Delta Air Lines,Northwest Airlines, United Airlines,United Parcel Service, and US Airways

Non-U.S.—All Nippon Airways, along withBritish Airways, KLM Royal Dutch Airlines,and Scandinavian Airlines System, representingthe Association of European Airlines (AEA)

INDUSTRY ASSOCIATIONSEuropean Association of Aerospace Industries (AECMA), General AviationManufacturers Association (GAMA),International Civil Aviation Organization(ICAO), National Business AviationAssociation (NBAA), Air Transport Association (ATA), National Air Transportation Association (NATA),National Air Carriers Association (NACA),and International Federation of Air LineDispatchers’ Associations (IFALDA)

MANUFACTURERSAirframe — Airbus Industrie, The BoeingCompany, Bombardier, Cessna, and GulfstreamEngine — GE Aircraft Engines,Pratt & Whitney, and Rolls-Royce

PILOTS’ ASSOCIATIONS Air Line Pilots Association (ALPA),Independent Association of Continental Pilots (recently merged with ALPA),Allied Pilots Association (APA), Coalition of Airline Pilots Associations (CAPA),International Federation of Air Line Pilots’Associations (IFALPA)

REGULATORS U.S. Federal Aviation Administration (FAA),Transport Canada, Joint Aviation Authorities(JAA) of Europe as represented by the U.K.Civil Aviation Authority (CAA), DirectionGénérale de l’Aviation Civile (DGAC) France,and Civil Aviation Safety Authority (CASA)Australia

OTHER PARTIESAir Crash Victims Families Association (ACVFA)

ARAC ETOPS WORKINGGROUP PARTICIPANTS


ETOPS AuthorizationThe ARAC has recommended that FAR 121.161 (the60-Minute Rule) and associated guidance and advisory

material be revised to■ Establish the basis and requirements for operating

twin-engine, turbine-powered airplanes beyond 60 min of flying time (at single-engine cruise speed with no wind and in standard conditions) of an adequatealternate airport.

■ Apply this same regulatory framework to the operation of turbine-powered airplanes with more than two enginesbeyond 180 min (at one-engine-inoperative cruise speedwith no wind and in standard conditions) of an adequatealternate airport, and also make it applicable to all opera-tions in polar areas (see Polar Operations, p. 10).

■ Make the designed and certified operating capabilities of the airplane type the basis for determining the maximumdiversion authority of that type.

■ Define allowable diversion authorizations for differentregions of the world based on the overall operationalneeds of each region.

■ Apply current ETOPS best practices to all extended operations.

It should be noted that, although these proposed ETOPSrequirements are consistent for all jetliners, the thresholdvaries at which they would take effect. For two-engine airplanes operating under FAR Part 121, ETOPS will be in effect — as is currently the case — on routes where the airplane is at some point more than 60 min flying time from an alternate airport. For FAR Part 121 operations byairplanes with three or more engines, these new ETOPS rules will apply on routes that are at some point more than180 min from an alternate airport. They also will apply toall operations in the polar regions (i.e., the areas north of78°N latitude and south of 60°S latitude).

DefinitionsThe ARAC has proposed that ETOPS-applicable definitionsbe added to FAR Part 121. Many of the terms used in the newregulations and guidance material for ETOPS are unique toextended operations and demand precise definition to ensurecommon understanding and proper compliance.

To encompass all extended-diversion-time operations, notjust those flown with two-engine airplanes, the term ETOPSwould be redefined as extended operations (as used in thisarticle) and shall no longer mean extended-range operationswith two-engine airplanes. Another noteworthy change is theaddition of the term ETOPS alternate, which is an airportthat meets stated requirements for planned diversion use andat which the weather conditions are at or above the operatingminimums specified for a safe landing. This new term wouldreplace the current ETOPS term suitable, which denotes an alternate airport that is both above required weather

minimums and available for diversion use. Under the newrules, suitable would no longer have an ETOPS-specificmeaning; where it appears in the new regulations and asso-ciated guidance material, therefore, it should be interpretedonly according to its broadly accepted, everyday definition.

It should be noted that long-range operations (LROPS) is not proposed as an ETOPS term. Although used by somesegments of the global industry, LROPS currently does not appear or have legal standing in the FARs. The ARACETOPS Working Group did not propose adding LROPSbecause the term would be misleading — extended opera-tions are defined by distance to an alternate airport, not byoverall length of flight — and because it invites confusionwith the similar but unrelated term ultra-long-range operations, which deals primarily with flight crew duty time, crew rest, and other human-factors issues.

CommunicationsCurrent regulations require reliable communications. Re-cognizing that advances in technology occur and that verbalcommunications can be particularly valuable, the proposedrule promotes the adoption of voice communications forextended operations.

This proposed rule states that the most reliable com-munications technology—voice based or data link—shallbe installed in all airplanes operating beyond 180 min froman alternate airport. Alternative means of communicationmust also be available in the event the most reliable means is not available for any reason (e.g., lack of satellite coverage).Examples of these communications technologies (e.g.,SATCOM voice link, SATCOM data link, HF data link) are given in the associated guidance material.

The proposed rule is not intended to require operators tocontinually upgrade existing installations on an incrementalbasis. Rather, the rule is meant to further the adoption, as appropriate, of new technologies that significantly enhancethe quality and reliability of communications. One example of such innovation is today’s transition from HF radio to satellite-based technologies.

DispatchThe ARAC has proposed a new regulation specifying airplane dispatch requirements for ETOPS alternate airports.The operator would have to select en route alternate airports that meet the weather requirements set forth in itsoperations specifications.

Because alternate airport weather is checked before air-plane departure, and weather conditions can vary over time,the conservative weather minimums required for dispatch are higher than those that would be required to perform an instrument approach at that alternate airport. As proposed,this dispatch rule further requires the crew to verify the continuing availability of a valid alternate airport by meansof en route weather updating at the beginning of the ETOPSphase of flight. For this en route updating, the crew wouldbe required to ascertain only that the planned alternate is

9AEROSecond-Quarter 2003 — April

above normal landing minimums, not above the higher minimums applied before dispatch.

One of the distinguishing features of ETOPS is the identification of and reliance on alternate airports to whichairplanes can divert should an unscheduled landing becomedesirable or necessary. Under this proposed regulation, op-erators flying three- and four-engine airplanes in extendedoperations would be required to designate ETOPS alternateairports within 240 min, or if beyond 240 min, designate thenearest available ETOPS alternate.

Propulsion-Related DiversionsThe ARAC has proposed no substantive change to the rule that governs diversion following an in-flight engine failure or shutdown. However, the committee did offer guidance to further clarify existing diversion requirements for two-engine airplanes in the event of engine failure or shutdown.

To aid flight crews, the proposed guidance lists factors (e.g., airplane condition and systems status, weather condi-tions en route, terrain and facilities at the alternate airport)that the pilot in command should consider when decidingwhich alternate airport to divert to. To ensure that safetyalways remain paramount, the ARAC further identified factors that shall not be considered sufficient justification for flying beyond the nearest available alternate airport (e.g.,additional range capability based on remaining fuel supply,passenger accommodations beyond basic safety, mainte-nance and repair facilities at the available alternate airports).

Fuel ReserveThe ARAC has proposed that all airplanes flown in extendedoperations shall carry an ETOPS fuel reserve to protect the passengers, crew, and airplane in the event of a cabindepressurization followed by a low-altitude diversion.

Cabin depressurization is a very rare event that can occuron any jetliner and is largely unrelated to the number ofengines. If it does occur, the flight crew must immediatelydescend to an appropriate altitude, as defined by oxygenavailability or oxygen systems capability. A diversion is then generally required because of the increased fuel consumption of turbine engines at low altitudes and thecorresponding reduction in range.

This ETOPS fuel reserve requirement assumes thatdecompression would occur at the most critical point alongthe route in terms of total fuel consumption (a concurrentengine failure is further assumed if it would add to the total).The reserve thus calculated would ensure sufficient fuel foran extended low-altitude diversion followed by a descent to 1,500 ft at the alternate airport, a 15-min hold, and an approach and landing. Further allowance is made for possible airframe icing and wind forecasting error.

Following extensive review of data related to the accuracyof wind forecasting, as well as review of the icing scenariobased on the Canadian Atlantic Storms Program (CASP II),the ARAC proposed revising the ETOPS fuel reserverequirement. Under this proposed rule, two-engine airplanes

on extended operations would carry somewhat less reservefuel than in the past. Airplanes with more than two engineswould be required to carry an ETOPS fuel reserve for thefirst time, although many three- and four-engine operators do currently carry a depressurization fuel reserve as a matterof internal airline policy.

MaintenanceThe ARAC has proposed making current twin-engine ETOPSmaintenance standards applicable to all airplanes flown inextended operations. This would require three- and four-engine operators to also have an ETOPS maintenanceprogram in place before flying routes with the potential for an extended diversion.

ETOPS maintenance requirements have significantly re-duced the incidence of in-flight engine failures. Such eventscan be enormously costly and disruptive for airlines, which iswhy some operators of three- and four-engine airplanes havealready voluntarily raised their maintenance standards toETOPS levels.

Passenger Recovery PlanThe ARAC has proposed that all extended operators shalldevelop a plan to ensure the well-being of passengers andcrewmembers at diversion airports. This plan should addresstheir safety and comfort at that airport in terms of the facilitiesand accommodations and their retrieval from that airport.

Currently, passenger recovery plans are required only for cross-polar operations. Because diversions can occur anywhere, however, the ARAC has proposed that every operator flying routes over remote areas of the world should anticipate the possibility of a diversion within thoseregions and devise a plan outlining how it would recover the passengers, crew, and airplane.

Cargo Fire SuppressionTo further ensure safety, the ARAC has proposed that alltime-critical systems aboard airplanes flown in extendedoperations shall have sufficient capability to protect the airplane throughout the longest potential diversion for thatroute. In particular, each flight shall have continuous fire suppression capability for a period equivalent to the maxi-mum planned diversion time plus an additional 15 min tocover approach and landing at the alternate airport.

Two-engine airplanes flown in extended operations havemet this requirement since 1985. In contrast, although alljets have fire suppression systems, those with more than twoengines are not currently required to carry sufficient fire sup-pressant during extended operations to protect the airplanecontinuously throughout a maximum-duration diversion.

The ARAC has proposed that three- and four-engine air-plane operators that do not currently comply with this require-ment shall have six years after ETOPS regulations take effectto bring their existing fleets into compliance with this new rule.

Many airplane systems enhance safety during flight. Ofthese, cargo fire suppression is generally the most time-limited.

10 AERO Second-Quarter 2003 — AprilAERO

Proposed changes (continued)Applying ETOPS cargo fire suppression requirements to allextended operations can thus further protect passengers, crews,and airplanes on routes with extended diversion times.

Performance DataThe ARAC has proposed that existing regulations be modifiedto require that performance data be available to support allphases of extended operations. Flight crews and dispatchersmust have data available that describe the specific performanceof the airplane in normal and non-normal situations, includingthose that might be encountered during an extended diversion.

Polar OperationsThe ARAC has recommended that the North Polar area (i.e., everything north of 78°N latitude) shall be designated an area of ETOPS applicability. The same designation shall be applied to the South Pole and surrounding region(i.e., everything south of 60°S latitude).

Within these areas, ETOPS requirements shall apply to all airplanes, regardless of the number of engines or distancefrom an adequate airport. This proposed requirement recog-nizes the challenges associated with these areas and sets forth steps to protect diversion.

Polar operators require training and expertise to supportairplane diversions and their subsequent recovery. These operators must consider requirements for en route alternate airports, a strategy for and monitoring of fuel freeze, a passen-ger recovery plan, and reliable communications capability.

Rescue and Fire FightingThe ARAC has proposed a rule specifying rescue and firefighting (RFF) requirements at ETOPS en route alternate airports. If adopted, this rule will further ensure the safetyof all airplanes when flying extended operations, regardless of how many engines an airplane has.

Before dispatch, ETOPS operators have always had to designate alternate airports that are above ETOPS-specifiedweather minimums. In addition, these designated alternatesmust provide the necessary facilities and equipment to ensurethe safety and well-being of the passengers and crew through-out an extended diversion, after landing at the alternate airport,and for as long as they remain at that airport before beingretrieved. RFF capability is a key element of this protection.

During nearly two decades of ETOPS and more thanthree million ETOPS twinjet flights around the globe,there has not been a single landing accident following anextended diversion from the ETOPS phase of flight. Thefact that RFF services have not been needed does not

mean that such an event will never happen. Therefore, theARAC finds it prudent to formalize RFF requirements foralternate airports in the regulations.

Other Proposed ChangesThe proposed regulatory changes described above wouldaffect FAR Part 121, the section of the FARs governing the operation of transport-category airplanes. In responseto the FAA tasking statement, the ARAC ETOPS WorkingGroup also has proposed changes to other parts of the FARs.

In particular, the ARAC has proposed changes to FARPart 25, which governs the design and testing of transport-category airplanes, and FAR Part 33, which governs enginedesign and testing. If adopted, these regulatory modificationswill benefit the development of future transport airplanes —regardless of the number of engines—by formalizingETOPS-inspired improvements that have been shown inservice to further protect airplanes and reduce the likelihoodthat they will need to divert.

The ARAC has further recommended that operators mustcomply with all rules within FAR Parts 25 and 33 when considering the longest flight and longest diversion timefor which approval is sought. The rigor of this practice willensure that all airplanes designed to these requirementswill have the necessary redundancy and reliability to ensuresafe extended operations.

To further protect airplanes during extended operations,the ARAC has identified the factors that ensure high levelsof safety on flights with the potential for a long diversion. In the case of two-engine airplanes, the most significant element is propulsion system reliability.

Using several methods to assess risk, the ARAC con-cluded that diversion time can be significantly increasedwithout added risk if the IFSD rate is sufficiently low. AnIFSD rate of 0.01 per 1,000 engine-hours—or twice theengine reliability level required for 180-min ETOPS—hasbeen determined to allow unconstrained operations with two-engine airplanes. Currently, the world-fleet averageIFSD rates for the 767 and 777, which together perform the majority of ETOPS, are both below this threshold.

Other key elements that support extended diversion timesare proper testing and validation of an airplane type (i.e.,airframe-engine combination) to ensure ETOPS safety atservice entry. The Boeing 777 Early ETOPS programprocesses provided a successful template on which to basefuture such programs. Consequently, the design, analysis,and test features from the 777 Early ETOPS program areincorporated in the proposed ETOPS regulations.

OTHER INDUSTRY EFFORTSIn addition to this ETOPS-relatedARAC–FAA rulemaking, the EuropeanJoint Aviation Authorities (JAA) aredeveloping standards for extended operations. In light of the ARAC, JAA,

and other efforts taking place around theworld, the International Civil AviationOrganization (ICAO) — a branch of the United Nations — is reviewing thecurrent annexes and associated guid-ance materials and plans to propose

changes as appropriate for all airplanes.The Boeing Company supports the harmonization of aviation standardsamong regulatory authoritiesworldwide and actively supports theseJAA and ICAO efforts.


About the Authors

Capt. Chester“Chet” Ekstrandis vice president incharge of RegulatoryAffairs for BoeingCommercial Airplanes.He is responsible forissues and initiativesrelated to operationalsafety and serves as the company’sfocal for ETOPS. Capt. Ekstrand’sexpertise in workingwith the industry and regulatory authorities worldwide contributed significantly to the precedent-setting early ETOPS certification of the 777. Former positions include vice presidentof Communication, Navigation, Surveillance/Air Traffic Management and Extended-Range Twin-Engine Operations; vice president of Government and Industry Technical Affairs; director of Flight Crew Operations; chief pilot, flight training; and chief pilot, technical.

Mohan Pandey, senior manager of Operational Regulatory Affairs, has played a key role in almost every ETOPS operational issue. He led Boeing participation in the ARAC ETOPSWorking Group and currently serves as a member of the JAA and ICAO ETOPS committees aswell as the JAA Operational Steering Team. Mr. Pandey is a 30-year veteran of the aviationindustry and has held a variety of positions since joining Boeing in 1980.

As airplane range capabilities continue to increase, and flightsbecome more common in remoteregions of the world, expandingETOPS to embrace all extended-diversion-time operations — notonly those involving two-engine airplanes — will raise the industryto a higher and uniform standard.

The proposed U.S. ETOPS regu-lations reflect broad recognitionwithin the global aviation commu-nity that ETOPS-related practicescan further enhance the safety and reliability of all operations on routes with extended diversiontimes. The proposed rules recognizethe high standard of safety thathas been achieved during nearlytwo decades of highly successfultwinjet operations worldwide and are the next logical step inenhancing aviation safety.

The FAA will evaluate theseARAC-proposed regulations, makewhatever changes it deems ap-propriate, and publish the resultsin an NPRM for public review andcomment. After comment resolu-tion, the FAA is expected to enactthe new ETOPS rules, perhaps assoon as late 2004.

S U M M A R Y


CAPT. RAY CRAIG737 CHIEF PILOT

FLIGHT OPERATIONSBOEING COMMERCIAL AIRPLANES

DREW HOUCKASSOCIATE TECHNICAL FELLOW

FLIGHT DECK DISPLAYSBOEING COMMERCIAL AIRPLANES

ROLAN SHOMBERASSOCIATE TECHNICAL FELLOW

FLIGHT MANAGEMENT COMPUTERSBOEING COMMERCIAL AIRPLANES

13Second-Quarter 2003 — April AERO

Boeing will soon offer a suite of new integrated flight deck navigation options that enhance the provenapproach capability of 737-600/-700/-800/-900 airplanes. Available in 2003, these options enable pilots tofly precise three-dimensional paths that smoothly intercept a variety of final approach legs. The Category IIIBAutoland, Global Navigation Satellite System Landing System, Integrated Approach Navigation, and Naviga-tion Performance Scales options work together or separately to improve safety and performance while decreasing operating costs. F L I G H T O P E R A T I O N S

737-600/-700/-800/-900


GNSS LANDING SYSTEM

The 737-600/-700/-800/-900 GNSSLanding System (GLS) option usesGlobal Positioning System navigationsatellites and a Ground-Based Augmentation System (GBAS) to provide signals similar to InstrumentLanding System (ILS) signals (fig. 2).Ultimately, the GLS could replace theILS as the primary means for guidingairplanes to the runway in low visibility.The GLS also might be expanded to support curved approaches. (See“Global Navigation Satellite SystemLanding System,” Aero no. 21,January 2003.)

The initial 737-600/-700/-800/-900GLS option supports a Category Iinstrument approach capability and theability to complete the approach withan automatic landing. This system isbeing expanded to support fullCategory IIIB Autoland operations.

Retrofit for the 737-600/-700/-800/-900 GLS requires new multimodereceiver (MMR) hardware and soft-ware, a navigation control panel withGLS capability, hardware and softwareupgrades for the enhanced ground

14 AERO

CATEGORY IIIB AUTOLAND

The new 737-700/-800/-900 Category IIIB Autoland option (fig. 1)provides the same all-weather, pre-cision approach autopilot guidance currently available on other Boeing airplane models.

This option, which is in flight test,will be offered with the 737-700/-800/-900 over-under engine format. Theover-under format provides the displayspace necessary for Category IIIBAutoland system messages. (The737-600 is not currently being certifiedfor Category IIIB operation.)

1

2perators will be able toenhance the approachcapability of their 737-600/

-700/-800/-900 airplanes this yearwith a suite of new flight deck navigation options: Category IIIBAutoland, the Global NavigationSatellite System (GNSS) LandingSystem, Integrated Approach Navigation, and Navigation Performance Scales.

Together with the excellent existing approach capabilities of the 737, these options offer a flexible navigation solution for airlines that want to increase their competitive advantage byimproving airplane safety and performance, decreasing operatingcosts, and reducing flight crewtraining requirements throughadvanced technology.

The new navigation optionswork together or separately toenable pilots to fly safe, stable,and precise three-dimensional paths that smoothly intercept a variety of final approach legs.

The options improve landingcapability in adverse weather conditions, in areas of difficult terrain, and on existing difficultapproach paths. It addition, theywill allow crews to take advantageof emerging air traffic control technologies designed to improveairport operations.

To help operators understandthese navigation options and theirfeatures, this article describes

1. Category IIIB Autoland.

2. GNSS Landing System.

3. Integrated Approach Navigation.

4. Navigation Performance Scales.

The article also discusses how the options and procedures are compatible with current and emerg-ing approach navigation technolo-gies such as the Instrument LandingSystem, mixed-mode, and constant-angle nonprecision approaches.

O

CATEGORY IIIB AUTOLAND DISPLAY

FIGURE

1

AERO 15Second-Quarter 2003 — April

proximity warning system (EGPWS),flight management computer (FMC)U10.5 software, and common displaysystem (CDS) Block Point 2002 soft-ware. A future curved GLS approachcapability might require autopilot andCDS software changes.

The U.S. Federal AviationAdministration (FAA) plans to deployGLS ground stations in Memphis,Chicago O’Hare, Juneau Alaska, Seattle,Phoenix, and Houston to support opera-tional evaluation testing. The programcalls for the purchase and deploymentof as many as 40 ground stations peryear after the initial phase. The FAAprojects a total of 160 GBAS groundstations are needed in the United States.Europe also plans to develop and install GBAS ground stations.

INTEGRATED APPROACH NAVIGATION

Integrated Approach Navigation (IAN) is an approach option designed for airlines that want to use ILS-like pilotprocedures, display features, andautopilot control laws for nonprecision(Category I) approaches. This option

does not require additional groundfacility support.

The FMC transmits IAN deviationsto the autopilot and display system. The pilot procedures for IAN are derivedfrom current ILS pilot procedures andare consistent for all approach types:

3

Select the approach on the FMC control display unit, tune the appro-priate station, and arm the autopilotapproach mode. The IAN function sup-ports the ILS for glideslope inopera-tive, localizer only, and backcourseapproach types.

The IAN function will alert the crew to approach selection or tuninginconsistencies. For example, if an ILSstation is tuned and an area navigation(RNAV) approach also is selected on the FMC, the flight crew will bealerted and the ILS approach mode will take precedence automatically,with the appropriate display format.

While the IAN display (fig. 3) is similar to an ILS display, there are sufficient visual differences toensure that the crew does not confuse a nonprecision IAN approach for a precision ILS or GLS approach (fig. 4).As on all nonprecision approaches,the altimeter is the primary method of ensuring that altitude constraintsare honored.

Retrofit of this option involves soft-ware updates for the FMC, CDS, flightcontrol computer, and digital flight dataacquisition unit (DFDAU) and hardwareand software updates for the EGPWS.

GLS DISPLAY

FIGURE

2

IAN DISPLAY

FIGURE

3

16 AERO Second-Quarter 2003 — April16 AERO

NAVIGATION PERFORMANCE SCALES

Navigation Performance Scales (NPS)is a new display feature that integratesthe current lateral navigation (LNAV)and vertical navigation (VNAV) withactual navigation performance (ANP)and required navigation performance(RNP). The primary display format of the NPS (fig. 5) can be interpretedeasily, thereby allowing the crew tomonitor flight path performance relativeto flight phase requirements and air-plane system navigation performance.

NPS can be especially valuable for approaches with tight airspacerestrictions because of terrain, traffic,or restricted areas. LNAV and VNAVwith NPS supports Category Iapproaches down to 0.10-nmi RNP.NPS also is designed to smoothly transition to an ILS, GLS, or IANapproach. (For a detailed description of NPS, see “Lateral and VerticalNavigation Deviation Displays,”Aero no. 16, Oct. 2001.) Retrofit of this option involves software updatesfor the FMC, CDS, and DFDAU.

4

This year, operators will be able to enhance the approach capabilityof their 737-600/-700/-800/-900airplanes through a suite of newflight deck navigation options:Category IIIB Autoland, GLS, IAN,and NPS. These options enablepilots to fly paths that smoothlyintercept various final approachlegs. This integrated, flexibleapproach navigation solutionimproves safety and performanceand decreases operating costs. The options are designed to meet the current and futureapproach requirements of Boeingcustomers worldwide.

DISPLAY DIFFERENCES FOR IAN NONPRECISION AND ILS PRECISION APPROACHES

FIGURE

4

NPS DISPLAY

FIGURE

5

SUMMARY


About the Authors

Capt. Ray Craig has been with Boeing Commercial Airplanes since 1990. Currently chief pilot for the 737, Capt. Craig has served as senior project pilot for 737 Engineering FlightTest and 737 Production Flight Test.

Drew Houck is an Associate Technical Fellow with 10 years of experience in the Boeing Flight Crew OperationIntegration and Avionics System Display groups. Key projectsinclude flight deck display software development and test forthe 777, 737-600/-700/-800/-900, and 767-400 airplanes.

Rolan Shomber is an Associate Technical Fellow with 19 years of experience in flight management system design anddevelopment, with expertise in navigation, guidance, and displays.He is active in the development of required navigation performanceconcepts and Boeing flight management systems capability.


Additional FMC enhancements arebeing studied or developed to furtherimprove LNAV and VNAV approachoperations, including

Approach option/ capability

Category IIIB Autoland

GNSS Landing System

Integrated Approach Navigation

Navigation Performance Scales

Instrument Landing System

Description

■ All-weather, autoland capability■ Matches Category IIIB capability available on other Boeing airplane models■ Not currently offered for 737-600

■ New augmented satellite landing system■ Does not require a dedicated ground station for each runway■ Proposed as potential follow-on to current ILS stations■ Supports Category I operation in initial implementation■ Retrofit requires MMR and EGPWS hardware and software, FMC and CDS software, and a new navigation control panel

■ Nonprecision Category I capability with display similar to current ILS■ FMC-generated glidepath and final approach course■ Integrates with ILS localizer and backcourse approaches■ Retrofit requires EGPWS hardware and software and FMC, CDS, flight control computer,

and DFDAU software

■ Supports RNAV Category I procedures■ Integrates ANP and RNP capability with current LNAV and VNAV capability■ Supports curved approaches■ Integrates with ILS, GLS, or IAN final approach capabilities■ Retrofit requires only software changes

■ Currently available on 737-600/-700/-800/-900■ Well-established procedures■ Supports Category I and II operations■ Integrates with IAN■ Many ILS ground stations may be deactivated in the future

New Navigation Approach Options ComplementInstrument Landing System Capability

■ LNAV missed approaches, whichenable the crew to arm and engage anLNAV missed approach by pressingthe takeoff/go-around button. Thisoption reduces crew workload duringa busy period in the flight deck.

FMC Enhancements to Improve LNAV and VNAV Operations

■ Branching missed approaches,which allow one of several preplanned missed approach procedures to be engaged for the applicable approach leg.


■ A constant rate of descent along anapproximate 3-deg approach paththat intersects the landing runwayapproximately 1,000 ft beyond theapproach end and begins not laterthan the final approach fix or equivalent position.

■ Flight from an established heightabove touchdown should be in a land-ing configuration with appropriate

The safety benefits of stabilized finalapproaches, both nonprecision and precision (fig. A), have been recognizedfor years. The Global PositioningSystem makes stabilized approachespossible at many airports around theworld. NPS, IAN, and GLS all takeadvantage of this technology to pro-vide consistent, intuitive displays and associated procedures that support stabilized approaches.

The following excerpt (source:The Boeing Company, copyright1997) is from Controlled Flight Into Terrain Education and TrainingAid, section 3:

Unstable approaches contribute to many incidents/accidents. Pilots should establish a stabilized approachprofile for all instrument and visualapproaches. A stabilized approach has the following characteristics:

Safety Benefits of Stabilized ApproachesCOMPARISON PROFILE OF STABILIZED APPROACHES

FIGURE

A

and stable airspeed, power setting,trim, and constant rate of descent andon the defined descent profile.

■ Normally, a stabilized approach configuration should be achieved no later than 1,000 ft AGL in IMC. However, in all cases if a stabilized approach is not achievedby 500 ft AGL, an immediate missed approach shall be initiated.


FLY-TO CONVENTION

FIGURE

C

Displays and Procedures Are Similar to ILSThe current ILS remains the basicapproach capability. To minimizetraining requirements, new 737-600/-700/-800/-900 approach options usedisplays and pilot procedures that aresimilar to those used with the ILS (fig. B). For example, the new optionsinvolve the established fly-to con-vention, where a lateral pointer on the right of the center scale referenceindicates a lateral path to the right ofthe current aircraft position (fig. C).

The 737-600/-700/-800/-900 dis-plays include an explicit annunciationat the top of the attitude indicator thatclearly defines the source of the dis-played deviation scales and pointers.The approach data block, which in-cludes the selected station and courseand distance measuring equipment distance, is retained in the GLS andIAN approaches although modified tosupport their unique characteristics.

The 737-600/-700/-800/-900 pro-cedures have been human engineeredto ensure that, although their appear-ance and operation are consistent with an ILS, aircrews easily can differentiate among approach types(fig. 4, p. 16).

STANDARD ILS FORMAT

FIGURE

B

New Approach Navigation Option Displays and ProceduresDovetail With Current and Emerging Technologies


Mixed-Mode ApproachesUnder certain circumstances, pilots may choose to mix modes (fig. D). Forexample, figure E shows an InstrumentLanding System localizer (ILS LOC)approach with vertical navigation path (VNAV PTH) vertical guidance.The procedures for mixed-modeapproaches are straightforward, and the display formats are consistent and easy to interpret.

Constant-Angle Nonprecision ApproachesMany airlines are moving away from the traditional “dive and drive”step-down procedures and are introducing new constant-anglenonprecision approaches (CANPA). In conjunction with the autopilot,lateral navigation, and ver-tical navigation, CANPAsdecrease workload duringapproach by allowing the flight crew to loadmost required data beforebeginning the approach.

The new 737-600/-700/-800/-900 navigation displays allow the flightcrew to easily and intui-tively evaluate the status ofthe entire approach againstan objective flight technicalerror scale and pointer.Flight technical error isa measure of the accuracywith which the airplane is being controlled relative to the defined flight path.Deviations can be causedby the autopilot, crew response to the flight directors, orexternal environmental conditions such as a wind gradient or turbulence.

MIXED-MODE LOCALIZERAND VNAV PTH

FIGURE

D

ILS LOC APPROACH WITH VNAV PTH VERTICAL GUIDANCE

FIGURE

E


MAINTENANCE

OF HIGH-STRENGTH COMPONENTS

Many landing gear, flap supporting, and flapactuating components on Boeing airplanes aremade of high-strength alloy steels. Operationaladvantages are realized when these high-strength, high-heat-treated materials are used inlimited-space envelopes. To reap the benefits ofhigh-strength alloy steel components and avoidpotential safety issues resulting from damage,airline maintenance and overhaul personnel needto follow proper maintenance procedures andrework practices, checklists, and guidelines during component maintenance and overhaul.

M A I N T E N A N C E RALPH M. GARBER

ASSOCIATE TECHNICAL FELLOW

COMMERCIAL AVIATION SERVICES


CRAIG DICKERSON

LEAD METALLURGICAL ENGINEER

BOEING MATERIALS TECHNOLOGY



ALLOY STEEL

24 AERO Second-Quarter 2003 — AprilAERO

operators achieve the benefits asso-ciated with high-strength alloy steelsand avoid potential safety issuesresulting from damage caused bystress concentrations, detrimental sur-face conditions, corrosion, improperprocessing, or other factors.

This article discusses some

factors that cause damage in service or during overhaul. Most can beattributed to a lack of familiarity with high-strength alloy steels.Operators usually recognize the benefits of using these steels; how-

ever, certain characteristics of thesteels are not always given properconsideration during componentmaintenance or overhaul. Thesecharacteristics, including sensi-tivity to corrosion pitting, sus-ceptibility to microstructural damage resulting from embrittle-ment, and notch sensitivity, canlead to rapid crack growth in some load environments.

This article describes

1. Benefits of high-strength alloy steel.

2. Importance of proper inspection and rework.

3. Guidelines for reworking high-strength alloy steel components.

any landing gear, flaptrack, flap carriage, and

other flap actuating components on Boeing airplanes are made ofhigh-strength alloy steels, such as 300M, Hy-Tuf, 4340M, and 4330M.These components provide structural benefits (e.g., reliable, durable design)and strength characteristics that permit an efficient use of availableairframe space. Other steels inuse, including 9Ni-4Co-0.3C,AerMet 100, and precipitation-hardened stainless steels, havesimilar maintenance and over-haul requirements. (Note: High-strength alloy steels referencedin this article generally havebeen heat-treated above 180 ksi[180,000 psi]; most have beenheat-treated above 220 ksi.)

Airline personnel should follow proper maintenance procedures and Boeing-providedrework practices, checklists,and planning guidelines duringmaintenance and overhaul ofthese components. This will help

M


BENEFITS OF HIGH-STRENGTHALLOY STEEL

Components made of high-strengthalloy steel generally weigh less andrequire less space to house than compo-nents made of lower strength alloys.Using high-strength alloy steel for com-ponent design provides an opportunityto do the same job with less material.When properly maintained and overhauled, high-strength alloy steelcomponents demonstrate high levels ofservice reliability.

The decision to use high-strengthalloy steels is based on weight and eco-nomic factors. Airframe space for gearcomponents may be reduced because of smaller diameter shock strut com-ponents, smaller pins (reduced space for joints), smaller diameter trucks andaxles, and, in some instances, smallerdrag brace, side brace, and attach fit-tings. By reducing the space requiredfor these components, the wheel wellsize can be minimized and aerodynamicsurfaces can be optimized, which allowan increase in fuel tank size (optimalwing spar location) or additional spacefor other uses.

The use of high-strength alloy steelparts is economical because it reducesweight, thereby allowing for more efficient aerodynamic surfaces and providing the potential for increasedpayload and fuel.

For example, the trailing edge of the wing is relatively shallow. Usinghigh-strength alloy steel flap tracks,flap carriages, and flap actuating com-ponents reduces the profile and decreasesspatial envelope requirements whilemeeting or improving aerodynamicrequirements. This also optimizes wingshape and reduces the potential need forbulging aerodynamic surfaces, which in turn reduces drag and increasesairplane performance.

IMPORTANCE OF PROPERINSPECTION AND REWORK

Following proper rework practices and using Boeing-provided documentsduring maintenance and overhaul arenecessary to achieve the benefits associated with high-strength alloy steel components and help ensure safeairplane operation.

Airline personnel who participate incomponent rework, maintenance, andoverhaul tasks should be familiar withthe properties of high-strength steelsand understand the negative effects thatcan result from■ Sensitivity to stress concentrations

(notch sensitivity).

■ Microstructural damage from embrittlement or overheating.

■ Detrimental surface conditions.

■ Corrosion.

■ Improper processing.

Improper rework practices can resultin unscheduled maintenance or surfacedamage that causes crack initiation.Maintenance efforts focus on corrosionprevention and removal in addition tonormal checks for wear and free play.

High-strength alloy steels can ex-perience rapid crack propagation fromstress corrosion under certain loadingconditions. Therefore, surface damagedetection is important during overhauland on components in service.Removing visible surface corrosionbefore pitting begins (such as during a C-check) helps prevent conditions that can lead to crack initiation. Thebest safeguard against corrosion is to ensure that finishes conform to thedesign and that design improvementsare incorporated as minor changeswhenever possible.

Components manufactured from steel alloys heat-treated above 180 ksi(180,000 psi) should be reworked inaccordance with guidelines inComponent Maintenance Manuals(CMM) 32-00-05, 32-00-06, and

32-00-07. Although these guidelinesapply directly to landing gear com-ponents, they can be used to plan theoverhaul rework of all high-strengthsteel components. Standard OverhaulPractices Manual (SOPM) 20-10-01generally is specified in each CMMsection for the rework of wing compo-nents (e.g., flap tracks, flap carriages).For repair of high-strength, 300M steelparts on DC-10 and MD-11 airplanes,use CMM 20-11-02; for DC-9,MD-80, MD-90, and 717 airplanes,use CMMs 20-10-18 and 20-10-06.

In addition, airline personnel need to understand the importance of main-taining component finishes while in service (in situ, or on the airplane).This includes repairing damaged finishes to prevent corrosion and en-suring that solvents and materials thatcome in contact with the finishes donot result in premature degradation and unscheduled component removal.

Boeing documentation describes the methods for detecting base metaldamage while in service and duringoverhaul. Common techniques includedetailed visual inspections and othernondestructive inspection methods,such as magnetic particle inspection(MPI) and fluorescent penetrant inspec-tion (FPI). (See SOPMs 20-20-01 and20-20-02.) Ultrasonic or eddy currentinspections also may be useful for in situ inspections.

Boeing also is developing sup-plemental, specialized techniques,such as the Barkhausen inspection, todetect base metal heat damage underchrome plating or other protective finishes. This technique can be used successfully to screen components withsuspect damage. For example, if an axlefractures as a result of chrome-grindingheat damage during manufacture oroverhaul, the Barkhausen inspectionallows other suspect components to bescreened without first performing achrome strip and temper etch (e.g., nitaletch) inspection on all suspect axles.

1 2

26 AERO Second-Quarter 2003 — April26 AERO

GUIDELINES FOR REWORKINGHIGH-STRENGTH ALLOY STEELCOMPONENTS

This section provides guidelines forreworking high-strength alloy steelcomponents and describes some of the implications of improper reworkprocedures.■ Stress concentrations.

■ Overheating components.

■ Hydrogen embrittlement.

■ Cadmium embrittlement.

■ Improper finishing.

STRESS CONCENTRATIONS

During component design, eliminatingor minimizing areas of stress concentra-tions is a key objective. Special atten-tion is given to protective finish runoutsadjacent to stress concentration details.In addition, all stress concentrationdetails are subject to extensive testingand/or analysis to ensure that no detrimental effects are introduced into a part. Any rework or repair must notincrease stress concentrations thatdegrade component durability.

High-strength alloy steel components(along with those made from othermaterials) are shot-peened to create ashallow layer of compressive residualstress at the surface. This layer helps to■ Minimize the effects of stress

concentrations in transition areas.

■ Impede crack initiation and initialcrack growth caused by fatigue orstress corrosion.

■ Create a surface that will have minimal adverse effects from theresidual stresses of plating.

When a surface is machined orground to remove damage, thereworked area should be shot-peenedwith proper overlap onto the existingshot-peened surface. During overhaul,personnel must observe the platingrunouts specified in the CMM sectionsand SOPMs 20-10-01 and 20-42-03.

For example, when a coating such as chrome or nickel plating is applied

to surfaces to prevent wear or corrosion,the coating must exhibit proper runoutsthat terminate before the tangent of fil-let radii, edges, or other shape changes.Boeing SOPM guidelines should be fol-lowed for the rework of any componentand for all types of plating or coating.Rework or overhaul of componentsshould not introduce stress concentra-tions, or otherwise increase stresses,which can reduce the service life of acomponent below that of the originaldesign configuration.

Stress concentrations can lead to initiation of cracking by fatigue, stresscorrosion, or hydrogen-assisted stress corrosion. These cracks mayresult in a fracture or scrap of a com-ponent when found while in service or during overhaul. The following areexamples of stress concentrations thatcan lead to cracking.

Transitions or radii that are sharperthan original design. When removingdamaged material from part surfacesduring rework, the new transitions orradii should not cause an unacceptableincrease in stress concentration at thelocation or degrade the original designfeatures. When locally machining outcorrosion or damage during overhaul,a gradual transition into the reworkeddepression is necessary.

The intent is to remove the leastamount of material possible whileensuring that all discrepant material isremoved and the original designstrength and durability are maintained.There are few options to restore thesemachined depressions to meet interfacerequirements. One type of rework oroverhaul, sulfamate-nickel plating, iscommon on shock strut cylinder diame-ters and is used to repair lug faces todesign dimensions as follows:■ Local blends on inner cylinder outer

diameter surfaces and outer cylinderinner diameter surfaces often arefilled with sulfamate-nickel platingto restore them to dimensions thatare suitable for subsequent chromeplate application.

■ Spot facing on lugs is controlled tohave a generous radius at the tran-

sition to the adjacent surface andusually is kept at the minimum depthnecessary to clean up the damagedsurface. Spot face depressions typi-cally are not filled with plating torestore the dimension but instead arefinished in the same manner as theoriginal design. Spot face transitionradii need to be such that they can be shot-peened to the requirements of the adjacent surfaces.

■ When the entire face of a lug mustbe machined to remove damage, thenew lug transition radii should beshaped and positioned in accordancewith CMM requirements. Surfacetransitions into the lug hole and atthe lug edges must have design tran-sitions that will allow restoration ofshot-peening on all reworked areasand permit complete seating of bush-ings without contacting hole edges.

Abrupt changes in sections, holes,and sharp-cornered keyways should be avoided. Proper design will reflect generous fillets, gradual changes ofshape, and the use of relief grooves inareas of high stress. Finer surface fin-ishes also may be needed to eliminateunnecessary stress concentrations,especially in areas of machined radii or undercuts. Overhaul should reflectthe same careful, detailed review thatoccurred during the original design.

Plating conditions and runout con-trols that are not in accordance withdesign standards. During overhaul,many landing gear components arecompletely stripped to replace nickeland chrome plating. In most instances,these repairs involve rework of the base metal. The new plating depositsfrequently are thicker than the originaldesign configuration.

In all cases, it is important to adhereto the SOPM recommendations. Thiswill ensure that the restored plating is of high quality and that it does notterminate with an abrupt edge. Through-thickness cracks in chrome plate (gen-erally present where there is evidence of chicken-wire cracking) can lead to corrosion at the base metal interface

3


and deterioration of the plating ad-hesion. Through-thickness crackingalso can lead to fatigue or stress corrosion cracking of the base metalbeneath the plating.

Visual evidence of chicken-wirecracking after chrome grinding indi-cates poor chrome quality and also mayindicate the possibility of base metal heatdamage. Chicken-wire cracking notedin SOPM 20-10-04 indicates that thechrome should be stripped and replated.

If the plating runouts are blended ormachined to remove the abrupt platingedge, the techniques must be well con-trolled to avoid damaging the adjacentbase metal. Improper blending canremove the required shot-peened layeror create undercuts or grooves at theedge of the plating that can causecracking in service.

Several in-service fractures havebeen attributed to improper platingtechnique, poor-quality plating,improper runout conditions, and basemetal damage caused by poor blendingor machining control.

Proper use of special plating tech-niques, such as conforming anodes androbbers, can control plating thicknessesand runouts. This can reduce the possi-bility of chrome chicken-wire crackingand poor runout details.

Plating into a transition (radius transition or undercut) will create astress concentration that can causecrack initiation. For example, figure 1shows an outer cylinder clevis platedinto the lug transition. In service,fatigue cracking initiated

at the platingrunout led tolug fracture.

Corrosion and pitting.Corrosion pitsare stress con-centrations. Asthe pit forms,it damages theshot-peenedlayer locally at the surface.The pit thengrows throughthe compressivelayer, and thechange in resid-ual stress stateand the pitgeometry initiatestress corrosioncracking. This type of cracking mostoften occurs on surfaces that are bothprone to corrosion and exposed to sus-tained tensile stresses while in service,such as the lower surface of landing geartrucks, axles, and the surfaces of forwardand aft trunnions.

Corrosion pitting also can lead tofatigue crack initiation depending onthe component, the location of pitting,and cyclic loading conditions. In thesecases, the cracks can propagate to thecritical length and result in ductile fracture of the component. The degreeof cracking tolerated before fracturevaries by component, crack location,and component loading conditions.

To prevent excessive corrosion, thor-ough visual inspections should be per-formed on a regular basis to evaluatethe condition of the protective finishes.Damage should be repaired soon afterit is found. Touching up damage to ac-cessible enamel and primer in a timelymanner can prevent the formation ofcorrosion pits and reduce the need forexcessive rework during overhaul.Rework that requires low-hydrogen-embrittlement (LHE) cadmium stylusplating should be performed when thecomponent is not loaded.

When the component is removed

CRACK INITIATION AT CHROMEPLATE RUNOUT INTO RADIUS

FIGURE

1

FINISH DAMAGE ALONG LOWER ID SURFACE AND AREAS OF CORROSION PITTING AT FRACTURE ORIGIN

FIGURE

2

for overhaul, all evidence of corrosionmust be removed and finishes restored to design requirements or better. The sequence of rework operations is provided in CMMs 32-00-05, 32-00-06,and 32-00-07.

Landing gear truck fractures haveoccurred in service because of corro-sion on the inner diameter of the maingear truck beam (figs. 2 and 3). Thesefractures may be caused by a combina-tion of degraded protective finishes onthe truck inner diameter, poor drainage,and contact with the corrosive chemi-cals in washing solutions or deicingcompounds. Truck fractures most oftenoccur at maximum ground loads suchas after fueling or during preflight taxi.

Figures 4 and 5 show a drag bracefrom which corrosion was not removedcompletely during overhaul. The partwas subsequently shot-peened, and new protective finishes were appliedover the residual active corrosion. This resulted in crack initiation andpropagation while in service and theeventual fracture of the component.

Mechanical damage. Stress concentrations can be created bymechanical damage that compromisesthe protective finishes and alters thecompressive shot-peen layer. This

AERO28 Second-Quarter 2003 — April

damage often is caused by impropermaintenance practices such as jackingadjacent to a jack pad or an inadvertentimpact with tools or ground-supportequipment (e.g., tow vehicles).Although high-strength alloy steels arehard and resist dents, scratches, andnicks, stress concentrations caused bymechanical damage can dramaticallyreduce the service life of a component.

High-strength alloy steel componentsalso can be damaged by mishandlingduring shop rework (e.g., dropping,impact), and in some circumstances, byforeign object debris. Possible mechani-cal damage to a high-strength alloysteel component should be evaluated bythe operator and repaired as needed.

If the damage is local and widespreaddeformations are not evident, repair maybe similar to that required for corrosionand pitting. All deformed material mustbe removed before refinishing; deformedhigh-strength steel alloy componentsmust not be straightened. ContactBoeing for assistance, if needed.

LOWER PORTION OF FRACTURED DRAG BRACE

FIGURE

4

CROSS-SECTION VIEW OF RESIDUAL CORROSION UNDER CADMIUM PLATING

FIGURE

5

CLOSE-UP VIEW OF CORROSION PITTING AT FRACTURE ORIGIN

FIGURE

3


OVERHEATING COMPONENTS

Overheating of components can changethe original steel temper and mechani-cal properties of the affected area.Overheating damage can be caused by■ Frictional heating while in service.

■ Abusive machining and grindingoperations during manufacture or overhaul.

■ Exposure to high temperatures during over-haul bake cycles.

■ Unusual conditions such as refused takeoffs and local fires.

The degree to which themechanical properties arechanged depends on the tempera-ture and duration of exposure.

Overheating can result inovertempered martensite (OTM) or untempered martensite (UTM)formations in the base metal.Both conditions can be detectedby a temper etch (i.e., nital etch)inspection of the base metal.UTM indications show whiteduring temper etch inspectionsand often are found withinpatches of OTM, which showdark gray to black during temperetch inspection. SOPM 20-10-02provides details about theinspection process and inter-pretation of the results.

Heat damage generally isremoved by carefully machin-ing the base metal. Afterward,another temper etch inspectionis done to ensure that themachining did not create moreheat damage.

UTM formations may be accompanied by heat-induced crack-ing within these overheated areas that,if left in place, can propagate while in service. Figures 6 and 7 show service-induced heat damage on theinside diameter of a main gear outercylinder. This component developedextensive frictional heat damage in the upper bearing contact area

as a result of improper clamp-up. The heat damage led to crackingthrough the cylinder wall. Salvage wasnot possible.

Less severe friction-induced heatdamage can be found on inner cylindersduring component overhaul. This dam-age, which occurs on a more frequentbasis, is caused by vertical motionagainst the lower bearing surfaces. This

CRACKED MAIN GEAR OUTER CYLINDER WALL

FIGURE

6 damage generally is shallow and can beremoved by machining. After overhauloperations are completed, the compo-nent is returned to service in accor-dance with CMM requirements.

When grinding chrome to finishdimensions, overheating the base metalcan create UTM and OTM formationsunder the chrome. Figures 8 and 9show a severe grinding burn on a mainlanding gear axle that resulted in a

fracture. Similar grinding burnsalso have led to the fracture offlap carriage spindle journals(figs. 10 and 11).

Any visible evidence ofchrome plate distress canindicate the likelihood of basemetal heat damage. Figures 12and 13 show a grinding burnthat led to the fracture of apivot pin. SOPM 20-10-04 andCMMs 32-00-05, 32-00-06,and 32-00-07 provide guide-lines that indicate whenchrome must be removed during overhaul.

Some heat damage is sosevere that the heat-treat con-dition of material is altered inadjacent areas. This widespreadreduction in metal hardness(Rockwell-C hardness readings)may indicate that the compo-nent cannot be salvaged. Axleheat damage caused by a wheelbearing fracture may lead tosuch a condition.

Shop procedures such as magnetic particle inspectionand LHE cadmium stylusplating can cause arc burns ifappropriate precautions are notmaintained during processing.Figures 14 and 15 show a

fracture resulting from an arc burnthat developed during LHE stylus cad-mium plating. (Note: In this article,cadmium plating means cadmium-titanium or LHE cadmium plating.)

Overheating will not alter the heat-treat conditions of the base metal if the temperatures are below the originaltempering temperature. However, thecomponent still may require special

NITAL ETCH INDICATIONS OF HEAT DAMAGEON ID OF MAIN GEAR OUTER CYLINDER

FIGURE

7


consideration (or rework) because ■ Shot-peening may be compromised

(heated above 400°F).

■ Cadmium embrittlement may occur(heated above 450°F with cadmiumplating present).

■ Chromate conversion coating maybe degraded (heated above 400°F).

■ Organic coatings or sealants maycrack or become brittle or discolored(wide range of temperatures).

These situations often occur whencomponents are ■ Inadvertently overheated in an oven.

■ Exposed to elevated temperatureswith some finishes intact or bushings installed.

■ Exposed to fire.

Residual cadmium often is left on a part during overhaul processing toprotect it from corrosion. The part isthen stripped of all cadmium and re-plated near the end of overhaul. Partswith residual cadmium should not beheated over 400°F during overhaul.

Bushings should not remain installedduring overhaul unless retained byspecific CMM requirements. Bushingsmust be removed to permit a thoroughinspection of the base metal and toavoid bushing-to-bore interface degra-dation during bake cycles. Design fin-ishes are restored and new bushingswith design interferences and dimen-sions are installed because bushing wearlimits do not apply during overhaul.

Wheel bearing fractures or high-energy refused takeoffs often result inhigh local heat on an axle. Discoloration

of the enamel, primer, orchrome or evidence of cad-mium damage on the innerdiameter of the axle mayrequire the heat-damagedcomponent be removedfrom service.

Overheating affectscomponents to variousdegrees; in some instances,only finish durability isdegraded. This may resultin a shorter than plannedtime between componentoverhauls. Contact Boeingfor assistance with ques-tions about repairing or salvaging high-strength alloy steel componentsthat appear to have been damaged byoverheating.

HYDROGEN EMBRITTLEMENT

Hydrogen embrittlement occurs when a high-strength alloy steel component absorbs hydrogen, whichis not removed in a timely manner in accordance with the SOPM (e.g., embrittlement relief baking).

When hydrogen remains in a component for an extended time, themicrostructural damage that developssignificantly degrades the mechanicalproperties of the steel. The infusedhydrogen migrates to areas of highstress (e.g., material internal stresses)and creates local microstructural dam-age. When the component is installedon an airplane, this internal damagecan lead to crack initiation and propa-gation, resulting in component fracture.

The elevated temperatures reachedduring hydrogen embrittlement relief

baking, which is performed directlyafter stripping or plating operations dur-ing overhaul, effectively remove hydro-gen generated during these operations.Processes that must be followed withrelief baking include chrome, sulfamate-nickel, and LHE cadmium plating; strip-ping operations; and many nital etchinspections. After hydrogen-generatingoperations, relief bake delay time limitsmust be observed to ensure completehydrogen removal. In general, the bestpractice is to initiate baking as soon aspossible following a plating operation.

The delay time between platingcompletion and baking start typically isobserved. However, when thick platingdeposits or multiple plating operationsare performed on a single component,the total time between initial platingstart and baking start is a key factorwhen determining the maximum delaytime allowed. For example, embrittle-ment relief baking must begin 10 hrafter sulfamate-nickel plating is com-pleted or within 24 hr after plating

FRACTURED MAIN LANDING GEAR AXLE

FIGURE

8 NITAL ETCH INDICATIONS OF HEAT DAMAGE ON OD OF AXLE AFTER CHROME REMOVED

FIGURE

9


begins, whichever results in the shortestoverall bake delay.

Figure 16 shows a flap track thatcracked because of hydrogen embrittle-ment 149 flight cycles after overhaul.Figure 17 is a scanning electron

FRACTURED PIVOT PIN

FIGURE

12

FRACTURE THROUGH FLAP CARRIAGE SPINDLE

FIGURE

10 GRINDING DAMAGE VISIBLE ON CHROME PLATE AT FRACTURE ORIGIN

FIGURE

11

CLOSE-UP VIEW OF PIVOT PIN OD AT FRACTURE ORIGIN

FIGURE

13

microscope view of a typical hydrogenembrittlement crack where separationoccurs along grain boundaries.Typically, hydrogen embrittlementcracks propagate rapidly once loads are applied to the part. In some cases,internal residual stresses are sufficient-ly high to cause cracking even before the part is installed.

CADMIUM EMBRITTLEMENT

Overheating LHE cadmium orcadmium-titanium plated componentscauses embrittlement of high-strengthalloy steel by cadmium, resulting in cadmium diffusion into the steel grain boundaries. Solid-metal

embrittlement by cadmium can occur at temperatures below the cadmiummelting point. These effects on thebase metal can begin to occur at 450°F,whereas the cadmium melting point is generally 610°F. The microstructuralanomalies resulting from cadmiumembrittlement can lead to componentfractures in service.

Determining whether cadmium hasmigrated into the grain boundaries ofcadmium-plated, high-strength alloysteel components requires destructivetesting of the components. If thesecomponents have been overheated,salvage may not be possible. However,if high-temperature exposure was

short and discoloration of the enamelor primer was minimal, the componentmay be a candidate for salvage. Slightor no discoloration of the enamel orprimer may indicate the cadmium plating was not heated to the extentthat cadmium embrittlement would be suspected. Boeing can assist in this determination.


IMPROPER FINISHING

Improper applicationof protective finishesduring manufacture or overhaul can lead to finish degradation,corrosion, and cor-rosion pitting, which can result in com-ponent fracture whilein service (figs. 2 and 3, pp. 27–28).Some cleaners andchemicals may accelerate finishdegradation and lead to corrosion.Operators should ensure that cleaners and chemicals are testedbefore use in accordance with Boeingdocument D6-17487, Evaluation of Airplane Maintenance Materials.Testing to these requirements willdetermine whether a cleaner or chemical is detrimental to protectivefinishes or base metal. However,long-term exposure to the solution or material still may adversely affect finishes.

Personnel must ensure that materialsused for activities such as cleaning anddeicing conform to Boeing documentD6-17487 requirements and willaccomplish the intended task (verifiedby the material provider or operator).Refer to the Aircraft MaintenanceManual for materials specified for air-craft cleaning and deicing. The CMMspecifies the materials for use in repair.

High-strength alloy steel compo-nents should be stripped completely

during overhaul (including removal ofbushings and bearings in all structuralcomponents). This allows a thoroughinspection of the base metal (a primarycomponent overhaul requirement) andensures that all finishes, including theLHE cadmium plating and conversioncoating, are restored to the original design requirements. This is addressedin an all-model Boeing service letterdated April 23, 2002, Overhaul of High Strength SteelComponents–Cadmium Strip

Required (e.g.,757-SL-20-036-A,767-SL-20-038-A,747-SL-20-062-A).

Restoration ofthe shot-peenedlayer during over-haul is importantto ensure that theshot-peen com-pressive residualstresses are main-tained or restored.Removing or

damaging the shot-peened layer canreduce the protection that this com-pressive layer provides against fatigueand stress corrosion crack initiation.Discontinuous shot-peening can leadto crack initiation at the tensile surfacestresses adjacent to edges of abruptcompressive layer runouts (no fade-out). All reworked surfaces must beshot-peened after removing materialdamaged by corrosion, heat, anddeformation.

As a rule, if material removal exceeds0.0015 in (or 10 percent of the Almenstrip intensity), the surface should thenbe shot-peened to CMM requirements.Exceeding shot-peen requirements isbetter than leaving areas without shot-peening. All portions of a componentthat are to be shot-peened should first be completely stripped; no cadmiumresidue should remain on the surface.

FRACTURED ACTUATOR BEAM

FIGURE

14

NITAL ETCH INDICATIONS OF ARC BURNHEAT DAMAGE THAT LEAD TO FRACTURE

FIGURE

15

VISIBLE CRACKS IN FLAP TRACK (ARROWS)

FIGURE

16

INTERGRANULAR FRACTURE CAUSEDBY HYDROGEN EMBRITTLEMENT

FIGURE

17


High-strength alloy steels are used

widely in landing gear, flap track, flap

support carriage, and flap actuating

components on Boeing airplanes. These

high-strength materials provide signifi-

cant structural benefits and can result in

a weight savings. These parts often are

selected for placement in limited-space

envelopes (e.g., wheel wells and wing

trailing-edge support structures)

because of their reduced profile or

smaller diameters.

With these benefits comes a need

for airline personnel to exercise

precise care when reworking high-

strength alloy steel components

during scheduled maintenance and

overhaul. They need to understand the

importance of maintaining component

finishes while in service, follow

proper rework practices, and use

Boeing-provided maintenance

procedures, planning guidelines, and

checklists during scheduled main-

tenance and overhaul processes.

Improper rework and overhaul

practices may result in loss of finish,

corrosion, and damage to or alteration

of the base metal, which may require

unscheduled maintenance between

overhauls. The resulting damage also

could precipitate crack initiation and

removal of the part from service.

Removing corrosion and restoring worn

interfaces on a periodic basis are the

main emphases of high-strength alloy

steel component overhaul rework.

Key benefits of proper rework

and maintenance practices include the

possibility of extending the gear or

component overhaul intervals (time

between overhaul). Operators also will

benefit from the enhanced reliability

and durability of high-strength alloy

steel components on their airplanes.

Operators should ensure that

proper SOPM and CMM documen-

tation is used during overhaul and

rework of high-strength alloy steel

components. The planning flowcharts

in CMMs 32-00-05, 32-00-06, and

32-00-07 are value-added guidelines

for planning the rework of any

high-strength alloy steel component

on a Boeing airplane.

Editor’s note: The SOPMs and CMMs identified in this article can be ordered through the Data and Services Catalog.

S U M M A R Y


About the Authors

Craig Dickerson has been a metallurgical engineer in the aero-space industry for 18 years. As leadengineer for the Boeing MaterialsTechnology Landing Gear DesignCenter support group and former leadengineer for the Fracture Analysisgroup, he is involved with all aspectsof landing gear structure materials

and processes, including detail part manufacture, in-serviceperformance, component overhaul, analysis of parts returnedfrom service, and accident and incident investigations.

Ralph M. (Mike)Garber has been astructures engineer inthe aircraft industry for 38 years, including28 years as lead engineer and the past 7 years as an AssociateTechnical Fellow. His primary responsibilitieshave involved design and certification analysis of the wing, empennage, nacelle struts, and landing gear with a focus on airline workshops and identifying design improvements toincrease durability and fatigue resistance. He is a licensed professional engineer and hasassisted in NTSB investigations and Boeing- and FAA-recommended structural changes.

identified for both steel and titaniumalloy components in production and as a substitute for chrome plating duringcomponent overhaul. Some repair agencies and airlines are purchasingequipment and preparing facilities forHVOF coating application during over-haul as an alternative to chrome plating.

MAINTAIN FINISH DURABILITY THROUGH PROPER WASHING,CLEANING, AND FREQUENTRELUBRICATIONProperly restoring the finish of high-strength alloy steel components to origi-nal design conditions during overhaulminimizes the effects of washing andcleaning solutions, solvents, and com-pounds on the structure. Design-qualityfinishes are less likely to degrade inservice. In addition, frequent relubri-cation of these components soon afterwashing protects finishes at lubricatedinterfaces. Relubrication intervals arespecified in the Aircraft MaintenanceManual (AMM) but generally are ad-justed based on operator experience.

Boeing continues to receive reportsof premature corrosion from operatorsthat use pressure-washing techniqueson their airplanes. The following guide-lines will help operators maintain thefinishes of their high-strength alloysteel components through heightenedawareness and knowledge about keyaspects of airplane washing processes.

Washing and Cleaning Techniques■ Operators should avoid using

high-pressure washing.

■ When cleaning landing gear and othermechanical, electrical, or hydrauliccomponents, operators must followthe requirements in the AMM procedure Remove Material AroundSensitive Components (e.g., 747-400AMM 12-25-01, p. 301, 2.A.[2]).

■ After washing landing gear and con-trol surfaces, operators should com-plete rinsing within the specified timeperiod. Rinsing must not be delayed.

■ Operators should cover joints without relubrication fittings to


avoid contamination from water and cleaning solutions.

■ If washing is done at the beginningof a scheduled maintenance period,operators should not wait until theend of the period to perform lubri-cation — the elapsed time may not be acceptable.

■ When flushing or rinsing landinggear assemblies, operators shouldreduce spray pressure, ensure thatthe nozzle is at least 12 in from thejoints, and replace the corrosion preventive compound after washing.(See the multimodel maintenancetip, “Airplane High PressureWashing,” May 18, 1999.)

Impact of Aggressive Washing onFinishes and Lubrication

■ Short-term exposure to materials thatnormally contact properly restoredfinishes, such as solvents, should notcause premature degradation or lossof finish requiring repair or unsched-uled removal between overhaul.However, premature corrosion anddeterioration can occur in servicewhen water or foreign material entersjoints as a result of spraying cleaningsolutions directly into joints. Thisaggressive washing technique dis-places grease and negatively affectslubricated joints even though immedi-ate relubrication will purge most con-taminates from the lubricated cavities.

■ Most corrosion-related cracking andfractures in service are aggravated byaggressive washing techniques andcorrosive solutions. To help ensurethat finishes do not degrade pre-maturely between overhaul, operatorsshould lubricate all greased bearingsand cavities no later than 12 hr afterairplane washing. Relubrication andreplacement of corrosion preventativecompounds within this time periodminimizes finish exposure to cor-rosive cleaning agents following airplane washing.

INCREASED USE OF TITANIUMALLOYS AND TUNGSTEN-CARBIDE COATINGSBoeing and the industry are workingtogether to develop thermal spray coat-ings to replace chrome plating. Thesecoatings, which currently are used insome production and repair applications,can be applied using the high-velocity oxygen fuel (HVOF) process. The twocoatings primarily in use are tungsten-carbide-cobalt and tungsten-carbide-cobalt-chrome.

These tungsten-carbide coatings canbe applied to steel and titanium alloys.Steels can be either chrome plated orcoated with tungsten-carbide. Titaniumalloys cannot be chrome plated but canbe coated with tungsten-carbide throughthe HVOF process. With this coating, thelighter weight titanium can be used inmore landing gear and flight controlapplications where high-strength alloysteels would have been used in the past,resulting in a weight savings.

Titanium alloys are being used moreoften in the design of new landing gearand flight control support structure.These materials, which are becomingmore readily available, exhibit higherstrength-to-weight ratios than do steelalloys. Titanium alloy componentsrequire less finishing, are more easilymaintained, are less prone to corrode inservice, and require less overhaul pro-cessing than most high-strength alloysteel components. The durable, HVOF-applied tungsten-carbide coatings broad-ens possible titanium alloy applications.

HVOF-applied tungsten-carbide coat-ings also provide multiple process bene-fits when compared with chrome plating:■ Embrittlement baking is not needed

after application because hydrogendoes not infuse into the base metal.

■ When grinding the coating to thedesired finish, overheating the basemetal is less likely.

■ Applying coatings using the properHVOF procedures and equipment cansave shop processing and flow time.

These benefits are driving more tungsten-carbide applications to be

High-pressure washing is detrimental and

should not be used under any circumstances.

Contact your region’s Boeing Customer Support vice president to facilitate support in the areas of flight services, maintenance services, spares, training, and technical services and modifications.

The AmericasTom BasacchiPhone 206-766-1121Fax 206-766-2205E-mail [email protected]

Asia-PacificBruce DennisPhone 206-766-2309Fax 206-766-1520E-mail [email protected]

EuropeDaniel da SilvaPhone 206-766-2248Fax 425-237-1706E-mail [email protected]

Middle East, Africa, Russia, and South Asia-PacificMarty BentrottPhone 206-766-1061Fax 206-766-1339E-mail [email protected]

FIELD SERVICE REPRESENTATIVES

If your Boeing Field Service representative cannot be reached,support is available at thefollowing numbers 24 hours a day:

Rapid Response CenterBoeing-designed airplanes:Phone 206-544-7555Fax 253-773-6606

Technical Support DeskDouglas-designed airplanes:Phone 562-497-5801Fax 206-544-0641

Spares orders/quotes:206-662-7141 (Information)206-662-7200 (Spares AOG)562-593-4226 (Douglas AOG)

LOCATION REPRESENTATIVE TELEPHONE

Boeing Commercial Airplanes

Director D. Krug 817-358-2006Atlanta (CQT) W. Ellis 404-530-8674/8678Atlanta (DAL) F. Piasecki 404-714-3129Bogota H. Sandoval 57-1-413-8218/8128Buenos Aires (ARG) M. Snover 54-11-4480-5126Chicago (AAL) L. Kuhn 773-686-7433Dallas/Ft. Worth (AAL) C. Fox 972-425-6206Dallas/Ft. Worth (DAL) D. Root 972-615-4539Dallas (Love Field) R. Peterson 214-792-5862/5887/5911Fort Worth C. Paramore 817-224-0560/0561/0564Houston C. Anderson 713-324-3611Houston (Hobby) D. Hendrickson 713-324-4192/3611Kansas City J. Connell 816-891-4441Louisville A. Andrus 502-359-7679Memphis D. Schremp 901-224-4839Miami R. Larson 786-265-8288Orlando D. Pemble 407-251-5906Orlando (BBJ) F. Gardiner 407-877-4030Port of Spain L. Richardson 868-669-0491Rio de Janeiro J. Bartashy 55-21-3393-8343Santiago R. Farnsworth 56-2-601-0171Sao Paulo L. Anglin 55-11-5092-3936Tulsa J. Roscoe 918-292-2404/2707

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2 4 - H O U R A I R L I N E S U P P O R T

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Director, acting T. Waibel 1-206-544-3450Auckland R. Lowry 64-9-256-3981Brisbane D. Bankson 61-7-3295-3139Honolulu (ALO) A. McEntire 808-836-7472Honolulu (HWI) R. Owens 808-838-0132Jakarta R. Tessin 62-21-550-8065/1020Kiev R. South 380-44-230-0017Kuala Lumpur M. Standbridge 60-3-7846-2569Melbourne E. Root 61-3-9280-7296/7297Moscow (ARO) V. Solomonov 7-095-961-3819Moscow (TRX) E. Vlassov 7-095-937-3540Mumbai R. Piotrowski 91-22-2615-7262/7179Nadi H. Kirkland 679-672-6071Sydney (IMU) B. Payne 61-2-9952-9596Sydney (QAN) W. Mahan 61-2-9691-7418Tbilsi E. Vlassov 995-32-922-542Yuzhno-Sakhalinsk E. Vlassov 7-095-937-3540

Director R. Nova 65-6732-9435/9436/9437Bangkok D. Chau 66-2-504-3493Ho Chi Minh J. Baker 9011-84-8-845-7600Incheon J. Nourblin NAManila T. Fujimaki 63-2-852-3273Narita A. Gayer 81-476-33-0606Okinawa E. Sadvar 81-98-57-9216Pusan K. Cummings 82-51-325-4144Seoul (AAR) J. DeHaven 82-2-2665-4095Seoul (KAL) G. Small 82-2-2663-6540Singapore A. Hagen 65-6541-6074Sung Shan R. Kozel 886-2-2545-2601Taipei (CHI) M. Heit 886-3-383-3023Taipei (EVA) D. Bizar 886-3-393-1040Tokyo (ANA) T. Gaffney 81-3-5756-5077/5078Tokyo (JAL) L. Denman 81-3-3747-0085/3977Tokyo (JAS) R. Saga 81-3-5756-8737

Director T. Lane 86-10-6539-2299 x1038Beijing K. Childs 86-10-6456-1567Chengdu G. King 86-28-8570-4278Guangzhou A. Shafii 86-20-8659-7994Haikou R. Wiggenhorn 86-898-6575-6734Hong Kong R. Brown 852-2-747-8945/8946Jinan P. Lavoie 86-531-899-4643Kunming T. Bray 86-871-717-5270Shanghai (CEA) M. Perrett 86-21-6268-6268 x35156Shanghai (SHA) D. Babcock 86-21-6835-8388Shenyang L. Poston 86-24-8939-2736Shenzhen S. Cole 86-755-2777-7602Ulaanbaatar P. Kizer 976-11-984-060Urumqi D. Cannon 86-991-380-1222Wuhan M. Nolan 86-27-8581-8528Xiamen Y. Liu 86-592-573-9225

Region 6Russia/SouthwestPacific/India

Region 7SoutheastAsia andJapan

Region 8China

AERO - Boeing

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