Cessna Single Engines...• Cessna has developed a structural inspection program to assure the...
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1 Cessna Single Engine Safety Initiative Please have your computer volume turned on for this presentation.
Transcript of Cessna Single Engines...• Cessna has developed a structural inspection program to assure the...
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Cessna Single Engine Safety Initiative
Please have your computer volume turned on for this presentation.
Presenter
Presentation Notes
• Cessna is introducing a new safety initiative for single engine airplanes. • This video explains the specific details as well as the reasons why Cessna is introducing this new initiative.
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Cessna Single Engine Airplanes
145,000 produced between 1946-1986 Average age is 42 years old Made of aluminum Certified CAR 3
Presenter
Presentation Notes
• Why is a new safety initiative required for Cessna single engine airplanes? The reasons for this new initiative can best be understood by first reviewing the history of these airplanes. • Approximately 145,000 airplanes were made between 1946 and 1986, making the average age of the Cessna single engine fleet 42 years old. • These airplanes were certified under the Civil Aviation Regulations (CAR) Part 3 which is the predecessor to the current Federal Aviation Regulations (FAR) Part 23. This means that when these airplanes were certified they had to meet strength requirements, but did not have life limit requirements or targeted inspection requirements to detect metal fatigue which is a requirement for airplanes certified in recent years.
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Single Engine Safety Initiative
Cessna has developed a structural inspection program to assure the continued safe operation of single engine airplanes
Visual inspection techniques are utilized to detect Corrosion Cracks caused by metal fatigue
Presenter
Presentation Notes
• Cessna has developed a structural inspection program to assure the continued safe operation of single engine airplanes. • This inspection program will be added to the airplane service manual. • The inspection program incorporates visual inspection techniques to detect corrosion and cracks caused by metal fatigue.
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Single Engine Safety Initiative
Why Inspect? Corrosion (rust) and metal fatigue are inevitable Corrosion and metal fatigue reduce the load
carrying capability of the airframe Like people, airplanes age, and more frequent
and intrusive inspections are required to maintain health (safety)
Presenter
Presentation Notes
• Why are additional inspections required for these airplanes? Corrosion (rust) and metal fatigue are inevitable. • Corrosion and metal fatigue do more than degrade the physical appearance of the airplane. Corrosion and metal fatigue reduce the load carrying capability of the airframe to the point where the airframe may no longer be able to safely complete its mission. • Like people, airplanes age. As people age, more doctor visits and more tests are required to make sure a person remains healthy. Similarly, airplanes are going to need more frequent and intrusive inspections as they age to keep them flying safely.
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What is Corrosion?
Corrosion is the attack on metal by an electrochemical reaction to the surrounding environment
Electrochemical corrosion can best be compared to a battery cell
2024-T3 (aluminum sheet)
Presenter
Presentation Notes
• What is corrosion? It is the attack on metal by an electrochemical reaction to the surrounding environment. • The most common alloy used in general aviation airframes is 2024, which is composed of aluminum, copper and small amounts of manganese and molybdenum. • The easiest way to describe corrosion is to compare it to a battery. In order to have corrosion, four elements must be present: (1) a metal that gives up electrons which is the aluminum, (2) another metal that accepts electrons which is the copper, (3) physical contact between the two metals which is the alloy and (4) a conductive liquid, typically water with a chemical impurity, touching the two metals.
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Corrosion Prevention
The key to corrosion prevention is to keep the airframe free of moisture (electrolyte)
A major contributing factor to corrosion is the environment. Corrosion is more likely to be found on airplanes operating in Coastal environments Areas that contain high amounts of industrial particles
and fumes in the atmosphere
Presenter
Presentation Notes
• The key to preventing corrosion is to keep moisture (electrolytes) away from the airframe. • While much of aircraft maintenance is predicated on flight time, corrosion is typically more dependent on calendar time and the environment in which the aircraft operates. • Airplanes that operate in coastal environments are particularly susceptible to metal corrosion. The combination of water and salt found in a coastal environment creates a powerful corrosive agent. Also, airplanes exposed to environments with large amounts of industrial particles and fumes in the air also have an increased risk of corrosion.
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Corrosion Prevention
There are several common options available to shield the aluminum from electrolytes including: Cladding Chemical Treatments Sealants Corrosion Prevention Compounds (CPCs)
Presenter
Presentation Notes
• To prevent corrosion, the aluminum needs to be protected from electrolytes. • Common options for protecting the aluminum include, cladding, chemical treatments, sealants and corrosion prevention compounds, commonly known as CPCs.
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Corrosion Prevention
Cladding 2024 sheet can be coated ("clad") with very thin
layers (.001”) of pure aluminum to protect from corrosion The sheet material is vulnerable when the cladding
is compromised such as at drilled rivet holes Chemical Treatments Alodine or other chemical treatments are used to
enhance the corrosion resistance of the pure aluminum cladding
Presenter
Presentation Notes
• The first option to protect the aluminum from electrolytes is cladding. • 2024-T3 sheet is typically coated with a very thin layer of pure aluminum to protect from corrosion. However 2024-T3 Alclad is vulnerable wherever the clad is compromised – at edges, rivet holes or if it is scratched. Most airframe corrosion occurs at seams and joints which is why cladding alone is not sufficient to protect from corrosion. • Additional steps are required to protect the metal from exposure to electrolytes. Chemical treatments such as Alodine enhance corrosion resistance.
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Corrosion Prevention
Sealants Paint is the most commonly used sealant for corrosion
protection A good paint job using modern polyurethane paints is the
best defense against airframe corrosion The airframe interior of most pre-1986 airframes were
not painted (primed) Corrosion Preventive Compounds (CPCs) Effective means for protecting those parts of an airframe
that were not originally protected from corrosion
Presenter
Presentation Notes
• Traditionally, sealants are used to provide corrosion protection with paint being the most commonly used sealant. Today’s modern polyurethane paints create a thick impenetrable barrier that lasts a long time – 10 years or more. A good paint job is the best defense against airframe corrosion. • Paint only protects the exterior of the airframe and most pre-1986 Cessna airplanes were not painted on the inside with primer. Once an airplane has been riveted together, it is difficult to paint the inside. • The industry has developed various corrosion preventive compounds (CPCs) that can be applied to the airframe interior. CPCs are an effective method of protecting the airframe from corrosion.
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Corrosion Prevention
Continual inspections and preventative maintenance are required to keep the airframe metal from corroding Thorough rinsing and cleaning of airplane will remove
salt and other corrosive agents Chipped or delaminating paint needs to be properly
striped or sanded and re-painted During severe weather or wet conditions, airplanes
should be covered and sheltered
Presenter
Presentation Notes
• Even with the use of the aforementioned corrosion prevention methods, continuous inspections and preventative maintenance are necessary to keep the airframe metal from corroding. • Thorough rinsing and cleaning of the airplane will remove salt and other corrosive agents. Extra attention is required in areas that are exposed including landing gear and wheel wells as well as areas where debris collects such as in joints, gaps and hinges. • Chipped or delaminating paint needs to be properly striped or sanded and re-painted. • Also, during severe weather or wet conditions, airplanes should be covered and sheltered from the elements.
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What is Metal Fatigue?
Metal fatigue occurs when a metal is subjected to repeated loading and unloading.
Eventually microscopic cracks will form and these cracks will grow until the structure can no longer hold the load and the structure will suddenly fracture
Presenter
Presentation Notes
• What is metal fatigue? Metal fatigue occurs when a metal is subjected to repeated loading and unloading. • Eventually, microscopic cracks will form and these cracks will grow until the structure can no longer hold the load and the structure will suddenly fracture. • A simple example of metal fatigue is bending a paper clip. Bending the paper clip up and down a few times will result in the failure of the paper clip in fatigue.
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Corrosion and Metal Fatigue
Corrosion and metal fatigue both reduce the load carrying capability of the airframe
Corrosion and fatigue are not entirely independent processes - corrosion affects the expected fatigue life of airframe parts Corrosion pitting creates a stress concentration which
leads to crack initiation and potentially faster crack growth
Corrosion reduces the thickness of a part and therefore increases the stress in the part
Presenter
Presentation Notes
• Corrosion and metal fatigue reduce the load carrying capability of the airframe. • Corrosion and fatigue are not entirely independent processes of decay. Corrosion affects the expected fatigue life of an airframe part. Corrosion pitting creates a stress concentration which leads to crack initiation and potentially faster crack growth. • Corrosion also reduces the thickness of a part and therefore will increase the stress inside the part. As a general rule of thumb, increasing the stress on a part by 10% can reduce the fatigue life by around 50%.
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Corrosion Examples
Cabin Interior – All Models Model 177/210 Cantilever Carry-Thru Model 177/210 Cantilever Wing Attachments Model 200 Series Elevators Main Landing Gear – All Models Strut Braced Wings
Presenter
Presentation Notes
• Corrosion has been found in many locations on Cessna single engine airplanes. Here are a few locations where corrosion is typically found.
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Cabin Interior – All Models
Cabin is susceptible to corrosion given that it: May leak when it rains May be stored in un-insulated hangar or on the flight line Stays warm as the airplane goes through thermal cycles
during flight Condensation will form on the interior skin Moisture is absorbed by insulation and upholstery materials
Not often treated with corrosion prevention products Headliner is not always removed during an annual
Presenter
Presentation Notes
• First is the cabin interior. The cabin is subject to corrosion for a number of reasons. • The airplane may leak when it rains. • It may be stored in an un-insulated hangar or on the flight line. • When the airplane flies, it goes through thermal cycles and condensation may form on the interior skin. That moisture is absorbed and retained by the insulation and upholstery materials. • Since, the interior is not often treated with corrosion prevention products and the headliner is not always removed during an annual, corrosion is likely to be found.
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Cabin Interior – All Models
Corrosion
Presenter
Presentation Notes
• This is an example of corrosion typically found in the cabin. There is significant corrosion on the wing spar beams which needs to be cleaned up and repaired.
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177/210 Cantilever Carry-Thru
Provides the primary means of carrying wing loads across the fuselage
Corrosion occurs when Ducting contacts lightening holes in beam, or Moisture accumulates on I-beam surface
Limited repairability
Presenter
Presentation Notes
• Another example of corrosion on the interior of the cabin is the Models 177 and 210 carry-thru beam. This beam is the primary means of carrying the wing loads across the fuselage. • Corrosion occurs when ducting contacts the lightening holes in the beam or when moisture accumulates on the I-beam surface. • The carry-thru beam has limited repairability since the amount of material which can be removed from the beam and still be able to carry the required loads is minimal.
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Models 177/210 Cantilever Carry-Thru
Carry-Thru Beam
Corrosion
Corrosion
Presenter
Presentation Notes
• Corrosion is typically found where the ducting contacts the edges of the lightening hole and on the horizontal surface of the I-beam.
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Models 177/210 Cantilever Carry-Thru
Corrosion
Corrosion Pitting
Corrosion
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Models 177/210 Cantilever Wing Attach Primary load carrying member Corrosion is common on the carry-thru lugs and
the wing attach fittings Tight fitting faces act as a moisture trap
Presenter
Presentation Notes
• On the outboard ends of the carry-thru are the wing attachment fittings. • These fittings are also primary load carrying members. Corrosion is common on the carry-thru lugs and on the wing attach fittings since the tight fitting faces act as a moisture trap.
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Models 177/210 Cantilever Wing Attach
Wing Attach Fitting
Carry-Thru Spar Lug
Wing Attach Fitting
Corrosion Pitting
Corrosion Pitting
Corrosion Pitting
Presenter
Presentation Notes
• The pitting is not limited to the lug surface as can be seen on the outboard end of the wing attach fitting in the right hand picture.
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Model 200 Series Elevators Foam filled trim tab and foam filled trailing edge Absorbs moisture
Results in corrosion Changes elevator balance
When trim tab skin thins due to corrosion, the actuator can pull the fasteners through skin and disconnect
Inspect for pinholes, surface roughness, bubbling Not repairable
Presenter
Presentation Notes
• Corrosion is often found on the foam filled trim tabs and trailing edges used on many of the Model 200 series elevators. • Moisture can cause internal corrosion between the tab and the foam when moisture condenses in the tab as the airplane is flown at higher altitudes. • The absorption of moisture by the foam can affect the elevator balance. If the trim tab skin thins enough due to corrosion, the actuator can pull the attaching fasteners through the skin and disconnect and potentially separate from the elevator. • The trim tab and elevator need to be inspected for pin holes, surface roughness or paint bubbling as these are signs of internal corrosion. The trim tab and trailing edge are not repairable, they must be replaced.
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Model 200 Series Elevators
Hole caused by corrosion
Crack
Presenter
Presentation Notes
• This picture shows an elevator trailing edge with internal corrosion. Paint bubbling, pin holes and small cracks are indications that significant corrosion is present on the underneath surface of the skin.
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Main Landing Gear Made from 6150M
High-Strength Steel A pit as small as .005”
can initiate a fatigue crack which will result in fracture of the gear
Keep surface painted with polyurethane paint and blend out pits per Service Manual
Flat Spring Gear
Rust
Presenter
Presentation Notes
• The next corrosion example is the main landing gear which is made from 6150M high-strength steel. • A corrosion pit as small as .005” deep can initiate a fatigue crack which will cause the gear to fracture. • Chipped or delaminating paint needs to be properly striped or sanded and repainted with a polyurethane paint. • The area around the cabin entry step is particularly susceptible to corrosion.
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Strut Braced Wing Front Spar Wing spar made
from several sheets of 2024-T3 aluminum clad riveted together
Strut attaches at wing splice joint
Corrosion observed in underlying sheets
Presenter
Presentation Notes
• The next example of corrosion commonly seen on Cessna single engine airplanes is the wing front spar on the strut braced airplanes. • The wing spar is made from several sheets of 2024-T3 Alclad riveted together. The wing spar web is spliced at the same location where the wing strut attaches. • Moisture enters the spar through the rivet holes, causing corrosion in the underlying sheets. In many cases, the corrosion is not discovered until a rivet is found missing. Once a rivet is missing, the underlying corrosion is likely to be severe and will require significant disassembly of the structure to repair.
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Strut Braced Wing Front Spar
Presenter
Presentation Notes
• Even though the wing surface looks good from the outside as depicted in the lower left hand picture, once the splice joint is taken apart, corrosion may be found on the inside surface.
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Strut Braced Wing Front Spar
Corrosion Product
Presenter
Presentation Notes
• This corrosion is reducing the load carrying capability of the wing. A careful inspection of the wing spar is required to look for corrosion product seeping out between the layers of the spar. If corrosion product is found additional investigation will be required.
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Strut Braced Wing Front Spar
Front Spar
Presenter
Presentation Notes
• Here is an example of a wing that has been disassembled due to corrosion. The corrosion is concentrated around the rivet holes where the original aluminum clad was breached.
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Metal Fatigue Examples
200 Series Horizontal Stabilizer Model 172/175 Horizontal Stabilizer Model 150/152 Vertical Stabilizer Attach Models 172/182/206/210 Forward Doorpost at
Strut Attachment Rudder Pedal Bar Assembly – All Models Engine Mount Truss
Presenter
Presentation Notes
• Cracking has been found in several locations on Cessna single engine airplanes. Here are just a few of the locations where fatigue cracking has occurred on Cessna single engine airplanes.
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200 Series Horizontal Stabilizer Front Spar
Crack
Cracks in Spar Web
Presenter
Presentation Notes
• Horizontal cracking has been found in the horizontal stabilizer front spar webs and spar attachment fittings on the Model 200 series. This cracking has been reported in airplanes with over 9500 hours.
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200 Series Horizontal Front Spar Attach
Crack
Presenter
Presentation Notes
• This is the horizontal stabilizer front spar attachment to the fuselage. Fatigue cracks can develop on higher time airplanes below the attachment boss.
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Model 172/175 Horizontal Front Spar
Cracks
Presenter
Presentation Notes
• On the Models 172 and 175, service experience indicates the possibility of cracks/buckles developing in the area aft of the center lightening hole in the horizontal stabilizer front spar. To prevent this condition from occurring, a one-piece front spar reinforcement is available (reference Cessna Service Bulletin SEB94-8). • Improper ground handling can cause cracking and deformation of the horizontal structure. A tow or steering bar should be used to move the airplane on the ground. The airplane should not be steered by pushing down on the horizontal stabilizer.
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Model 150/152 Vertical Stabilizer Attach
Crack
Presenter
Presentation Notes
• Cracks have been found in the vertical stabilizer attach fittings on the Cessna 150/152 airplanes. Cracks tend to form in the outboard portion of the fitting with the outboard strap failing before the inboard strap. • Since Cessna 150/152 airplanes are used for training, aerobatics and spins, these uses put additional air loads on the vertical tail surface, so a failure of this attach fitting would lead to a critical situation.
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Models 172/182/206/210 Forward Doorpost at Strut Attachment
Crack
Presenter
Presentation Notes
• Service experience indicates the possibility of cracks developing in the lower area of the forward cabin doorposts near the strut support fitting. Service kits are available to modify the doorpost structure if cracks are found.
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Rudder Pedal Bar Assembly – All Models
Crack
Presenter
Presentation Notes
• Cracks in the rudder bar assembly can lead to loss of rudder control and braking action. Typically these cracks occur at the weld and travel around and adjacent to the weld.
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Engine Mount Truss
Crack
Crack
Presenter
Presentation Notes
• Cracks have been found in the engine mount truss near the welded joints.
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Inspection Program Details
Inspections Based on field history Reviewed by customer focus group
Inspection Details Corrosion prevention and control program
Directed visual inspections for corrosion completed during annual
~15-20 visual inspections to inspect for cracks Borescope and magnifying glass required to complete
inspections ~5 inspections based on existing service bulletins
Presenter
Presentation Notes
• Now for the details of the new inspection program. The inspection program is based entirely on field history. The inspection document has been given to selected customers for their review and they all agree that the inspections are appropriate and necessary. • This inspection program is intended to be completed in conjunction with an airplane’s annual inspection. For a low time, well-maintained airplane, it is expected that the inspections can be completed in less than 10 hours. • The total number of inspections varies by airplane model. The inspections include a corrosion prevention and control program which calls for directed visual inspections during an annual. There are about 15-20 visual inspections to look for cracking and corrosion which will require a borescope or a magnifying glass. Another five inspections are based on existing service bulletins, so if the airplane has been maintained per manufacturer's instructions, then compliance has already been achieved.
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Specialized NDI techniques required When corrosion is found When cracking is suspected When required by existing service bulletin For high time airplanes (12,000+ hours) or severe usage
airplanes (6,000+ hours)
Inspection Program Details
Presenter
Presentation Notes
• Specialized NDI (non-destructive inspection) techniques are required in certain situations: when corrosion or cracking is found or suspected, when required by an existing service bulletin or for high time and severe usage airplanes.
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Inspection Program Availability
Revised inspection program will be published in the airplane service manual 200 Series airplanes – December 2011 100 Series airplanes – 2nd Quarter 2012 Compliance Date
200 Series airplanes – December 2013 100 Series airplanes – June 2014
Presenter
Presentation Notes
• The revised inspection program will be published in the airplane service manual in November for the 200 series and in the 2nd quarter of 2012 for the 100 series airplanes. The compliance date will be two years after the revised service manual is released.
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Conclusion
Safety is a partnership between owners, manufacturers and the FAA
Report anomalies to the Customer Service or Regulatory Authority
For more information contact: Cessna Customer Care 1-800-4Cessna (1-800-423-7762) option 2 [email protected] www.cessna.com/customer-service.html
Presenter
Presentation Notes
• In conclusion, Cessna has developed a new safety initiative for single engine airplanes to keep the fleet flying safely into the future. However, the safety of the fleet cannot be assured by Cessna alone. • Safety is a partnership between owners, manufacturers and the FAA or foreign regulatory authority. It takes all three working together to assure the fleet remains safe. Report anomalies to Cessna or the Regulatory Authority for the benefit of aviation community.
