Failure Analysis in Aeronautical Engineering
***
Journal
Gunma Prefecure
14 October 2024
Failure Analysis in Aeronautical Engineering
Page |2
Table of Contents
Table of Contents ...................................................................Ошибка! Закладка не определена.
I: Common Types of Failures in the Aeronautical Field ............................................................... 3
A: Identifying Types of Failures .................................................................................................... 3
B: Causes of Failure ...................................................................................................................... 3
II: Testing Methods For Failure Analysis ...................................................................................... 4
A: Preventative Methods: NDT and Destructive .......................................................................... 4
B: Forensic Testing Methods ........................................................................................................ 4
C: Relevant Standards .................................................................................................................. 5
III: Case Study on Japan Airlines Flight 123 .................................................................................. 5
A: Description of Event ................................................................................................................ 5
B: Investigation ............................................................................................................................ 6
C: Recommendations .................................................................................................................. 9
References ................................................................................................................................. 11
Failure Analysis in Aeronautical Engineering
Page |3
I: Common Types of Failures in the Aeronautical Field
A: Identifying Types of Failures
The margins of error in the field of aeronautics are very slim due to the conditions of flight requiring
very precise measures to ensure safety of those onboard. Several instances of error in planes include
structural errors pertaining to fatigue cracks and stresses on the fuselage, wings, and tail, mechanical
errors, which pertain to failures in moving parts of the aircraft, inlcuding flaps, hydraulics, landing gears,
and control surfaces, and electronic failures which involve the interference of the avionic software and
other flight control software issues. As an engineer, it is increasingly important to mitigate and prevent
accidents from occurring in aircraft due to the increased risk of fatality once airborne. Specifically,
structural problems are more prone to come up due to the fact that the rapid pressurization and
depressurization of the cabin can cause micro-cracks to form in the fuselage over time, ultimately
damaging the structure of the aircraft due to fatigue.
B: Causes of Failure
Human error is a major perpetrator of accidents in the modern aviation industry. Human error can range
from faulty repairs to improper piloting, and even improper communication from air traffic control.
Some motives behind human error include cost-cutting measures, negligence, and uncertainty. This can
be solved by selecting more qualified engineers and technicians and providing the necessary skills and
training resources to ensure the safety of the passengers inside the aircraft. This will also virtually
eliminate the factor of negligence in an aircraft crew, further ensuring that the aircrafts will operate
safely.
In addition to human error, improper maintenance and inspections prevail as the second-most
damaging cause of failure in the aviation industry. Industry standards have been set by both the FAA in
the United States and internationally by IATA, the International Air Transport Association. For instance,
Failure Analysis in Aeronautical Engineering
Page |4
FAA regulation 43.13-1B ensures that aircraft are adequately repaired frequently, with detailed
standards, repair, and testing procedures depending on the numerous materials used in aircraft
operating in the United States.
II: Testing Methods For Failure Analysis
A: Preventative Methods: NDT and Destructive
In the aviation industry, there is a great deal of preventative testing that needs to be done in order to
mitigate the risk of casualties in flight. By performing regular non-destructive testing (NDT), airlines and
manufacturers can identify early signs of wear, fatigue, corrosion, or cracks in critical parts like engines,
airframes, and landing gear, and composite materials [6]. This proactive approach allows for timely
maintenance and repairs, reducing the risk of catastrophic failures, increasing safety, and extending the
service life of aircraft, all while minimizing downtime and repair costs. As references [5, 6] state, NDT is
essential to prevent potential failures by evaluating tests that do not harm the material, making it
possible to efficiently and effectively test aircrafts at critical chokepoints in a timely manner. Some NDT
methods for the metal fuselage of the plane include hardness testing, magnetic testing, aluminum
testing, and vibration testing. These are accomplished with many different technologies such as
ultrasound testing and several software interfaces [5]. In most cases, it is more practical to use NDT
methods for preventative purposes due to the fact that there does not need to be any extra effort that
needs to be spent rebuilding the material as the material is not harmed in NDT processes.
B: Forensic Testing Methods
Forensic Testing, unlike preventative testing, occurs after an unfavorable incident to help engineers
learn from their mistakes to prevent further instances of that failure. Techniques in forensic testing are
not constrained by harming the material, so a combination of both NDT ultrasound material analysis and
destructive testing methods (cross-sectional analysis) are used. For instance, at plane crash sites,
samples of debris are tested to help scientists and engineers better understand the direct cause of the
Failure Analysis in Aeronautical Engineering
Page |5
failure and what factors led to the unfortunate incident. With the help of flight recording software, the
forensic analysis of aircraft failures has been eased by referencing the documentation of each of the
aircraft’s flights and activity.
C: Relevant Standards
Specifically to the aeronautical field, specific standards are specified to ensure safety and proper testing
methods. The governing bodies in the United States that set these regulations are the Federal Aviation
Administration (FAA), a subsidiary of the Department of Transportation, and the American Society for
Testing and Materials (ASTM). ASTM provides specific methods and regulations for how the tests should
be conducted based on the testing type (NDT or DT) and circumstance (forensic or preventative). In nondestructive testing to measure the growth rate of cracks from fatigue stress, ASTM E647-24 provides
specific standards for test preparation, crack monitoring, data collection, and exact crack growth rate
calculation models [2]. The FAA provides regulations on the size of the cracks allowed and other repair
and maintenance standards to ensure the safe flight of the aircraft. Regulation 43.13-1B from the FAA
specifically mandates protective coatings on top of aluminum fuselages in order to prevent cracks and
corrosion from external stresses and cyclic fatigues caused by rapid pressurization and depressurization
of aircraft cabins [1]. It is imperative that these regulations and standards are enforced to mitigate the
risk of potential mishaps in the aviation industry.
III: Case Study on Japan Airlines Flight 123
A: Description of Event
In August 12, 1985, a Boeing 747SR-100 was headed to Osaka from Tokyo Haneda International Airport.
Twelve minutes after takeoff, at 24,000 feet, a sudden rupture occurred in the rear pressure bulkhead, a
component of the plane in the aft of the aircraft that pressurizes the cabin [3]. This caused a rapid
decompression, leading to the loss of hydraulic systems and flight control, as well as the rupture of the
vertical stabilizer [4]. The pilots lost control of the aircraft, causing the plane to stall down and crash into
Failure Analysis in Aeronautical Engineering
Page |6
a mountain in central Japan. After 32 minutes of erratic flight, the plane crashed into Mount
Takamagahara in the Gunma Prefecture. The crash resulted in 520 fatalities, with only four survivors,
making this flight the deadliest single-plane accident in aviation history [3].
B: Investigation
Upon examining the prior repair reports of the aircraft with numerous chemical, ultrasound, damage
analysis, and microstructure analysis [3], the aircraft was sent to be repaired after a tailstrike landing
incident in 1978 [4].The rear pressure bulkhead was improperly secured with one row of rivets instead
of the required two rows of rivets as shown in figure 1 and 2 shown below. The repair job also was
missing the torque box skin, which holds the rivets together with a counter-force, securing the plate to
the pressure bulkhead. As shown in figure 2, the bays 4 and 5 comprise of the second rivet row needed
to secure the pressure bulkhead and had no rivets. Investigations in [3] show that the motive behind this
faulty repair was to cut repair and part costs. This caused the micro-cracks in the plate to form over time
as the cabin pressurized and depressurized rapidly. These cracks, due to the empty holes in bays 4-5 as
shown in figure 2, expanded and ultimately blew out the pressure bulkhead, causing the cabin to depressurize in mid-air. The immense force from the rapid de-pressurization caused the aft of the plane to
blow, causing the tail to break off.
Failure Analysis in Aeronautical Engineering
Page |7
Figure 1: A Close-up Diagram of the plate holding the pressure bulkhead. Left: Correct Repair Schematic. Right: Actual repair
schematic
Retrieved from [3]
Figure 2: Broader diagram of Aft Pressure Bulkhead, showing rivets and rivet bays. Retrieved from [4].
Failure Analysis in Aeronautical Engineering
Page |8
The faulty repair was not in compliance with the FAA guideline AC 43.13-1B standard due to the airline
not complying with the manufacturer’s instructions on repairing the bulkhead. The standard specifically
states that rivetting causes internal stresses within the material. To minimize the internal stresses of the
plate, the rivets must be drilled, countersunk, surface treated, and primed prior to installation. The FAA
standards do not have jurisdiction over Japan Airlines as their operations are outside the United States
of America. However, these standards act as a minimum requirement to comply to for the passengers’
safety and a prior revision of 41.13-1B was in effect during and prior to the time of the incident. As
found in the post-accident investigation, the plate that held the bulkhead had fatigue stress built over
the seven year period had formed cracks which have expanded. As shown in the studies by [2], cyclic
fatigue stress, like of those induced by rapid depressurization and pressurization, increases
exponentially over time in an equation modelled based on the material. For aluminum, which the
support plate was made of, this formula applies with material dependent constants multiplied and
added to the time factor and the exponent base to signify the properties of the material.
Figure 3: Schematic Diagram of Aft Pressure Bulkhead. Retrieved from [4].
Failure Analysis in Aeronautical Engineering
Page |9
F) Recommendations:
During regular inspections in that seven year period, this repair flaw was not caught and fixed, violating
several international aviation inspection compliances. As a result, new inspection protocols and
procedures were released in standard AC-120-73. This regulation requires proper training for repair
mechanics and inspectors while also releasing new inspection criteria to incorporate FAA-approved
standards in the international aviation industry [4].
Upon analysis of the failure of JAL Flight 123, the second row of rivets was meant to stop the
propogation of cracks. However, the cracks had spread throughout the entire pressure bulkhead and
managed to result in complete failure. The depressurization also resulted in the failure of the aft vertical
stabilizer, which is located at the tail of the aircraft, causing all hydraulic systems to malfunction and the
auxilliary power unit, ultimately leading to loss of control of the aircraft due to the fact that the
hydraulic systems are responsible for the proper steering and control of the aircraft. As a result, if
aircraft hydraulic systems were isolated, the pilots would have some control of the aircraft, making it
possible to safely land the aircraft at a nearby airport. In the studied case, the hydraulic systems were
isolated physically, but the proximity of the hydraulic systems to the auxilliary power unit in the rear of
the plane caused all four hydraulic systems to fail when the pressure bulkhead failed [4]. Alternatively, if
a hydraulic fuse was implemented aircraft, then the blow of the failure of the aft pressure bulkhead
would not have limited the control of the aircraft as much. The fuse would be in place to prevent the
loss of hydraulic fluid in the systems, regaining control of the aircraft. With modern innovations in
aircraft technology, fly-by wire is implemented to electronically control the rudders, elevators and
ailerons in the tail and wings of the aircraft, eliminating the need for hydraulic elements entirely. In the
event of a depressurization, pilots would still have partial control over the aircraft due to the fly-by wire
Failure Analysis in Aeronautical Engineering
P a g e | 10
installed in parallel throughout the aircraft so that if there is a failure, there always is an alterate route
for the signals to operate the necessary flight controls.
Failure Analysis in Aeronautical Engineering
P a g e | 11
References
[1] “Federal Aviation Administration, “AC 43.13-1B - Acceptable Methods, Techniques, and
Practices - Aircraft Inspection and Repair [Large AC. This includes Change 1.]” – Document
Information,” Faa.gov, 2019.
[2] American Society for Testing and Materials, “Standard Test Method for Measurement of Fatigue
Crack Growth Rates,” Astm.org, 2024. Available: https://www.astm.org/e0647-24.html
[3] Aircraft Accident Investigation Commission, Aircraft Accident Investigation Report. Gunma
Prefecture, Japan: Japan Ministry of Transport, 1987.
[4] Federal Aviation Administration, “Boeing 747-SR100 | Federal Aviation Administration,”
www.faa.gov, Jul. 18, 2023. Available:
https://www.faa.gov/lessons_learned/transport_airplane/accidents/JA8119
[5] D. Duarte, B. Marado, J. Nogueira, B. Serrano, V. Infante, and F. Moleiro, “An overview on how
failure analysis contributes to flight safety in the Portuguese Air Force,” Engineering Failure
Analysis, vol. 65, pp. 86–101, Jul. 2016, doi: https://doi.org/10.1016/j.engfailanal.2016.03.003.
Available: https://www.sciencedirect.com/science/article/abs/pii/S1350630716300632.
[Accessed: Sep. 28, 2021]
[6] R. Smith, S. Mukhopadhyay, A. Lawrie, and S. Hallett, “Applications of ultrasonic NDT to
aerospace composites,” Nov. 2013, Available: https://www.ndt.net/?id=14974. [Accessed: Oct.
05, 2024]