Lessons Learned

Technical Related Lessons:

Unrestricted fuel leaks during ground operation (taxi, takeoff, and landing), particularly those which breach the fuel tank, pose an extreme hazard to the aircraft and occupants. (Threat Category: Uncontrolled Fire)

  • As a root cause of this accident, a portion of a failed combustor penetrated a fuel access panel that was not impact resistant, creating a massive fuel leak in the left wing. Ignition sources were readily available from hot brakes and engine components, and the leaking fuel ignited, leading to an uncontrolled fire, which consumed the airplane, and resulted in a large number of fatalities. There was no capability on the airplane to mitigate or eliminate the associated hazards, leaving the airplane completely dependent on airport crash, fire, and rescue responses, a timely evacuation, and design/certification measures intended to limit the flammability of airplane materials and structure. Had impact resistant access panels been installed, it is possible that the fuel leak would not have occurred.

Fuel tank access panels should be designed to a level of impact/fire resistance appropriate to the expected threat. Fire and impact resistance must be considered in the design of components that fall within the tire and rotor burst zones, especially those whose failure could lead to an uncontrollable fuel leak. (Threat Category: Uncontrolled fire)

  • In this accident, a portion of the number nine combustor can penetrated a fuel access panel in the proximity of the engine. The ensuing fuel leak ignited, leading to the catastrophic fire. Following the accident, impact resistant panels were required to be installed in tire and rotor burst zones. Non-resistant (original) designs are allowed in non-vulnerable locations. For some design applications, the impact/fire resistant panels are able to be physically interchanged with the non-resistant design, and stenciling/placards are used to identify locations where fire/impact resistant panels are to be installed. 

(See schematics/pictures from a Boeing document describing the test used to determine the ability of various panel designs to withstand impacts equivalent to tire and engine failures.)

Emergency exit door function should be evaluated in the expected usage conditions (rapid door opening, etc.). (Threat Category: Cabin Safety/Hazardous Cargo)

  • During the evacuation, a cabin attendant attempted to open one of the cabin doors, only to have it jam as a result of his attempt to open it rapidly. This failure mode was not identified during door or evacuation testing, and only identified itself during an actual evacuation. The failure resulted in that particular door being unavailable, at least for the initial portion of the evacuation, and may have inhibited the evacuation process, possibly contributing to the catastrophic outcome of the accident. 

Passenger survivability can be substantially influenced by toxicity of smoke and gases from burning cabin material. (Threat Category: Cabin Safety/Hazardous Cargo)

  • A number of the fatalities in the accident resulted from inhalation of toxic vapor or substances that were byproducts of burning cabin material. Flammability standards at the time of certification of the 737 required that cabin materials not be combustible, or that when ignited, were self extinguishing within a short time period. The intensity of this fire overwhelmed the flammability resistance of the cabin materials. Toxic substances were released that incapacitated passengers, and prevented their evacuation from the airplane. Following several fire related accidents, the flammability standards of cabin materials were revised. 

Common Theme Related Lessons:

Engine repairs should be accomplished in accordance with clear instructions provided by the original engine manufacturer, or approved alternative procedures. If alternate procedures are used, an assessment of the effects on engine ratings, limits, margins, reliability, and subsequent maintenance and overhaul intervals and procedures should be accomplished. (Common Theme: Organizational Lapses)

  • The Pratt and Whitney JT8D engine on British Airtours 737-200 was repaired in accordance with procedures approved by the British CAA and were based upon information obtained from the engine manufacturer. Pratt and Whitney repair instructions provided general guidance for repairs which were accomplished, but there appeared to be confusion regarding the ultimate impact of the repaired engine regarding fatigue life. This misunderstanding resulted in the repaired combustor remaining in service beyond its fatigue life, and an uncontained engine failure resulted.

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