Jt15d Ata 72 Maint

Pratt & Whitney JT15D Series (CAT C)

ATA 72 – ENGINE (MAINTENANCE)

of 12 FOR TRAINING PURPOSES ONLY © JT15D - ISSUE 1, 2009




ATA 72– ENGINE - MAINTENANCE

0 TABLE OF CONTENTS

1 Turbine engine disk life 3 2 Rotor components – service life 3 2.1 Description 3 3 Hot Section Inspection (HSI) and Time Between Overhauls (TBO) 4 3.1 General 4 3.2 Time between overhauls 4 3.3 Hot section inspection 4 4 Engine performance 5 4.1 Purpose 5 4.2 Operation 5 4.3 Symptoms of engine deterioration: (@ Constant N1) 6 5 Engine condition trend monitoring (ECTM) 7 5.1 Purpose 7 5.2 Description 7 5.3 Data acquisition 8 5.4 Data entry and calculation 8 5.5 Plotting and Trend Analysis 9 6 Boroscope Ports 10 6.1 Purpose 10 6.2 Two locations 10 6.3 Area to inspect 10




1 TURBINE ENGINE DISK LIFE One of the most important aspects of turbine engine operation and maintenance and perhaps the one least understood is the requirement to control disk life. The limiting of disk lives is at present necessary because of the nature of the damage that occurs to disks in service and the extreme importance of disk integrity in view of the serious consequences should a disk fail. Without going into the details of the many parameters used to design disks, it is important to have an understanding of the major considerations facing engineering. These are:

burst margin (ultimate strength),

yield strength,

creep strength,

high frequency fatigue strength,

metallurgical deterioration, and

low cycle fatigue strength. Through highly developed methods, disks are designed so that the first four factors do not generally limit disk life. The fifth factor - metallurgical deterioration - may require disk life limitations, but is often overridden by the sixth factor, low cycle fatigue (LCF). LCF dictates life limitations and retirement of disks which physically appear to be quite satisfactory. A disk is subject to low cycle fatigue each time the engine starts and accelerates to power, and the disk is exposed to centrifugal loads. At the same time, large thermal gradients can be imposed on the disk. Rims which are relatively thin and exposed to the hot gases heat up faster than the thick hubs. The result is high tensile stresses in the disk bore. Through analytical and actual rig tests we establish, based on minimum material specification properties, that a part can be cycled from zero to max allowable engine speed X number of times. However, a typical flight does not only consist of a speed excursion from 0 to max and back to zero rpm. There are many fractions of full speed excursions, and these must be added to zero-max.

A program of residual life testing, which is conducted on disks retrieved from the field, is continually in process, and further time extensions are granted when feasible. The primary objective is to avoid disk failures, and economics or convenience must not be allowed to jeopardise safety.

2 ROTOR COMPONENTS - SERVICE LIFE

2.1 Description

Certain engine rotating parts are subject to low cycle fatigue due to cyclic operation related to time rather than flight cycles have to be considered. As a result, these parts must be replaced when either the cycle count or the hourly limit is reached. The operating life of the rotating parts must be monitored by a "Flight Count" method. Since low-cycle fatigue is a function of number of take-offs, and related speed and temperature change, the flight count must be recorded. Several other factors affecting disk life are related to "hours", and total operating hours may be therefore override the total cycle limit. A component must be replaced when either the total cycle limit or the hourly limit is reached. Thus, it is very important for an operator to record both the total running time

and the number of flights. Total cycles: NUMBER OF FLIGHTS X FLIGHT COUNT FACTOR

For details, refer to SB # 7002 NOTE: When a typical flight mission profile involves many touch-and-go

cycles and/or in-flight shutdowns, e.g. aircraft used for training purposes, contact P&WC Service Department for information.




3 HOT SECTION INSPECTION (HSI) AND TIME BETWEEN OVERHAUL

(TBO)

3.1 General

HSI and TBO are defined under the Service Bulletins no. 7003. Operators desiring TBO extension should submit a formal request in writing with details of sample engine log book to: Manager, Technical Support, JT15D turbofan engine.

3.2 Time between overhauls

Recommendations for time between-overhaul take into consideration the average effect of the many variables affecting overhaul life such as average flight duration, percentage of time at any given power level, climatic conditions and environment, maintenance practices, utilisation and engine modification standard. Under extreme conditions of very low utilisation coupled with continuous operation in salt water atmosphere or heavy sand environment, periodic inspections in accordance with the applicable maintenance instructions may indicate maintenance action prior to the recommended overhaul life.

3.3 Hot section inspection

HSI must be performed at mid TBO even if Engine Condition Trend Monitoring is conducted.




4 ENGINE PERFORMANCE

4.1 Purpose

Ensure engine performance is within the maximum allowable operating limits.

4.2 Operation

Using the chart, find the target N1 speed, maximum T5 temperature and maximum N2 speed, according to prevailing ambient conditions. Start the engine and set N1 to the target speed, stabilize the engine then record the actual N2 speed and T5 temperature. Ensure that the actual N2 speed and T5 temperature fall below the chart limits. NOTE: Always refer to the airframe manuals for performance chart and

complete procedure. The maintenance manual provides engine master curve charts. They should not be used to accept or reject engine performance.




4.3 Symptoms of engine deterioration:

(@ Constant N1)

4.3.1 Excessive high turbine tip clearance

N2 T5 Wf

4.3.2 High turbine stator distress

N2 T5 Wf

4.3.3 High pressure compressor deterioration

N2 T5 Wf

4.3.4 Interstage sealing ring leaks

N2 T5 Wf

4.3.5 External P3 air leak

N2 T5 Wf




5 ENGINE CONDITION TREND MONITORING

(ECTM)

5.1 Purpose

Engine Condition Trend Monitoring (ECTM) allows the user to monitor the engine performance

Permit early detection of engine deterioration

Help determine trouble area

Increase dispatch reliability

Perform repairs at the most economical time

5.2 Description

ECTM is a process of periodically recording engine and aircraft instrument parameters and comparing them to a computer reference model. Under specific ambient conditions, engine parameters such as compressor speed (N2), interturbine temperature (ITT) and fuel flow (WF) are predictable. The difference between the actual engine parameters and the computer model values will be plotted as 3 deltas using a graphical chart method. Once a trend is established by plotting the deltas, any deviation would indicate some engine deterioration. Analysis of the trend reveals extent of deviation and possible need for corrective action.




5.3 Data acquisition

The accuracy of the ECTM process depends on the quality of the data entered in the computer system. There is only one flight configuration where engine reaction can be predictable, cruise condition. The data will be valid if you apply the following restrictions:

Once per day, or every 6 hours if flown more often, select the flight with the longest cruise that is at a representative altitude and airspeed

Allow the engine to stabilize 3 to 5 minutes without ANY power lever movements

The same flight configuration must be repeated (i.e. electrical load, bleed air extraction)

Record data within a reasonable time frame

5.4 Data entry and calculation

ECTM data can be processed using IBM or compatible personal computer, in conjunction with Pratt and Whitney Canada supplied ECTM IV program.




5.5 Plotting and Trend Analysis

Once the deltas are calculated, the computer does

the plotting and displays the result on the screen or sends it to a printer. Analysis of the trend reveals extent of deviation and possible need for corrective action. NOTE: Aircraft Gas Turbine Operation

Information Letter (AGTOIL) no. 27

provides generic information in regard to engine trend analysis.




6 BOROSCOPE PORTS

6.1 Purpose

Various ports and access areas allow inspection of internal engine components without having to disassemble the engine.

6.2 Two locations

Exhaust duct tail cone

Intermediate case pad (12 o’clock, JT15D-4 series and JT15D-5 series)

6.3 Area to inspect

High pressure compressor impellor

No. 4 bearing area




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