SwissAir Flight 111
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This week in engineering news, Astrolab’s Flexible Logistics and Exploration (FLEX) Rover will be part of future Moon missions!
The FLEX rover will be the largest and most capable rover ever to visit the Moon.
FLEX is approximately 3 times the mass of other moon rovers with a maximum combined rover and cargo mass of more than 2 tons.
FLEX rover uses a modular system for transporting and deploying payloads, which should allow more flexibility on the missions that it can perform.
FLEX is designed to transport two astronauts across the Moon’s surface and also has a robotic arm and a science mast similar to NASA’s Mars rovers and also an antenna to provide constant high-bandwidth communication with Earth.
If you want to read more about the FLEX rover, check out the link on the web page for this episode at failurology.ca
Now on to this week’s engineering failure; SwissAir Flight 111, a McDonnell Douglas MD-11 that crashed off the coast of eastern Canada, claiming the lives of all 229 onboard.
SwissAir Flight 111 was a scheduled international passenger flight that operated between JFK International Airport in New York City to Cointrin Airport in Geneva Switzerland. The flight was popular with diplomats and other United Nations members as it was one of the only direct flights between NYC and Geneva, where the UN has offices.
SwissAir Flight 111 crashed 8 km (5 miles) off the coast of Peggy’s Cove, Nova Scotia, Canada, killing all 229 passengers and crew members on board. The Canadian Government spent $57 million in search and rescue response, crash recovery, and investigation into the cause of the crash.
Aircraft and Flight Crew
SwissAir Flight 111 was operated with a 7 year old MD-11 aircraft, a 3-engined, modern, widebody airline, derived from the DC-10. The aircraft was configured with 241 passenger seats with first class and business class having in-seat, in-flight entertainment systems; these entertainment systems were the first of its kind equipped on the airplane. The inflight entertainment systems allowed for browsing of the world wide web, ability to play games, and watch movies. Although we take IFE systems for granted now on aircraft, this was quite an advanced system for 1998.
The Captain of SwissAir Flight 111 was 50 year old Urs ZImmerman, a former Swiss Air Force fighter pilot with over 10,000 hours total flying time, 900 hours of which were on the MD-11. The First Officer was also a former Swiss Air Force pilot with 4800 hours flying time, 230 hours of which were on the MD-11.
Approximately 53 minutes after departure, while flying at FL330 (33,000’), the flight crew smelled an abnormal odor in the cockpit. A small amount of smoke became visible in the cockpit, then it is likely that the smoke stopped entering the cockpit for an undetermined length of time. The flight crew assessed that there was an anomaly associated with the air conditioning system.
After conversing with Air Traffic Control, the flight decided to divert to Halifax International Airport in Nova Scotia, Canada. While they were preparing to divert, the flight crew was unaware that the fire was spreading above the ceiling area in the front of the aircraft. No fire detection and suppression system was installed in the aircraft that could have alerted the flight crew to the presence of fire.
In accordance with the SwissAir checklist for smoke of unknown origin, the crew shut off power to the cabin, which also turned off the recirculating fans in the cabin’s ceiling. This allowed the first to spread to the cockpit, eventually shutting off power to the aircraft’s autopilot.
13 minutes after the abnormal odor was first detected, the aircraft's flight data recorder began to record a rapid succession of aircraft systems-related failures, likely as a result of the fire. The flight crew declared an emergency and indicated a need to land immediately. One minute later, radio communication and secondary radar contact with the aircraft was lost. Approximately 5 minutes and 30 seconds later, at 2231, Atlantic daylight saving time, the aircraft impacted the ocean 5 miles from Peggy’s Cove, Nova Scotia. Impact forces were estimated to be 350g, which caused the aircraft to disintegrate instantly.
Approximately 98% of the aircraft by weight was recovered from the ocean at a depth of 55 m (180 feet) through a combination of dredging, heavy lift operations, remote operated vehicles, naval and coast guard divers. The wreckage was brought ashore, washed, weighed, and cataloged, with items showing heat damage, burns, or unusual marks stored in a hangar at CFB Shearwater. The front 33 feet (10m) of the aircraft from the front of the cockpit to near the front of the first-class passenger cabin was reconstructed.
The Transportation Safety Board (TSB) determined that the fire most likely started from an electrical arcing event that occurred above the ceiling on the right side of the cockpit near the cockpit rear wall. The arcing event ignited the flammable cover material on nearby metallized polyethylene terephthalate (MPET) covering on the thermal acoustic insulation blankets. As the fire spread across the surface of the insulation blankets, other flammable materials became involved, including silicone elastomeric end caps, hook-and-loop fasteners, foams, adhesives, thermal acoustic insulation splicing tapes, and metallized polyvinyl fluoride (MPVF) insulation blanket cover material. The fire progression was rapid, and involved a combination of these materials that together sustained and propagated the fire.
Initial Wire Arcing
Reconstruction of the wreckage indicated that a segment of arced electrical cable associated with the in-flight entertainment network had been located in the area where the fire most likely originated. The Board concluded that the arc on this electrical cable was likely associated with the fire initiation event. The Board also concluded that it is likely that one or more additional wires were involved in the lead arcing event.
70 Airworthiness Directives (AD’s) were published by the FAA regarding one-time inspections of wires and electrical components in the front ceiling area of the aircraft.
During the lead arcing event, the associated circuit breakers or breakers did not trip. The Board concluded that although the type of circuit breakers used in the aircraft, including those used for the IFEN, were similar to those in general aircraft use, the circuit breakers were not capable of protecting against all types of wire arcing events. The Board recommended that a certification test regime be mandated that evaluates aircraft electrical wire failure characteristics under realistic operating conditions, and against specific performance criteria, with the goal of mitigating against the risk of igniting nearby flammable material.
Fire Detection and Suppression
The TSB analyzed airflow patterns and fire propagation in the aircraft to assess what cues may have been available to the pilots during the early stages of the fire. It was determined that the small amount of odor and smoke first noticed by the pilots originated from a small creeping fire started rearwards from the area of initial ignition, toward the area above the forward passenger cabin ceiling.
As the fire propagated rearward, it is likely that the associated smoke temporarily stopped migrating forward into the cockpit. As the aircraft was not required to be equipped with built-in fire detection in the hidden area where the fire was located, the pilots were not alerted to the presence of the fire. The Board concluded that the actions by the flight crew in preparing the aircraft for landing, including their decisions to have the passenger cabin readied for landing and to dump fuel, were consistent with them being unaware that an on-board fire was under way.
The Board issued several recommendations to mitigate against potential fires in hidden areas of aircraft, including a recommendation that appropriate regulatory authorities, together with the aviation community, review the methodology for establishing designated fire zones within the pressurized portion of the aircraft, with a view to providing improved smoke and fire detection and suppression capability.
By the time the crew was aware of the fire, the fire had developed to a condition where it is unlikely that available fire fighting equipment and methods would have been effective. The Board concluded that industry wide changes are necessary to provide aircraft crews with effective means to detect and suppress fires in hidden areas, including the provision for ready access to hidden areas for the purpose of firefighting.
System failure leading to increased fire propagation
During the fire, silicone elastomeric end caps installed on air conditioning ducts melted, which resulted in the addition of a continuous supply of conditioned air that contributed to the propagation and intensity of the fire. The cap assembly used on the stainless steel oxygen line above the cockpit ceiling was susceptible to leaking or fracturing when exposed to the temperatures that were likely experienced during the last few minutes of the flight. The Board recommended that, as a prerequisite to certification, all aircraft systems in the pressurized portion of an aircraft, including their subsystems, components, and connections, be evaluated to ensure that those systems whose failure could exacerbate a fire in progress are designed to mitigate the risk of fire-induced failures.
Standby instruments – Positioning and power supply
For at least some portion of the last minutes of the flight, primary flight displays ceased operating. A lack of outside visual references forced the pilots to rely on the standby instruments.
In the deteriorating cockpit environment, the positioning and small size of the standby instruments would have made it difficult for the pilots to transition to their use, and to continue to maintain the proper spatial orientation of the aircraft.
The Board called upon Transport Canada to work with the FAA and Joint Aviation Authorities to address identified safety concerns, including the lack of a power supply for the standby instruments that is independent of the aircraft electrical system and battery.
The Board believes that standby instruments should be in a standard grouping layout similar to the primary flight instruments, and that they should be positioned in the normal line of vision of the flight crew. The Board also believes that with current technology, providing independent standby instrumentation for secondary navigation and communication is feasible.
Additional safety risks identified
During the course of this investigation, some additional risks that have the potential to degrade aviation safety were identified. Although these factors could not be shown to have played a direct role in this occurrence, the associated deficiencies could potentially lead to other accidents if the deficiencies are not rectified.
Areas of concern
● checklists that do not adequately deal with smoke conditions;
● aircraft designs that do not facilitate the rapid de-powering of electrical systems;
● MD-11 map light design and installation;
● lack of clarity in guidance material and regulations regarding wire separation in confined areas; and
● inadequacy of Supplemental Type Certificate standards to ensure that add-on equipment is compatible with the aircraft's type certificate
In addition to the 14 safety recommendations that the Board has issued during the course of the investigation, nine recommendations are presented in the final report:
● Two recommendations that deal with testing and flammability standards of in-service thermal acoustic insulation materials.
● One recommendation that deals with the application of existing standards for the certification of other materials.
● Two recommendations that focus on aircraft electrical systems, including additional measures for certifying supplementary add-on systems and industry standards for circuit breaker resetting.
● Four recommendations that propose improvements to the capture and storage of flight data as it relates to cockpit voice recorders, flight data recorders, and cockpit image recording systems.
Safety action taken
As a result of the TSB's findings and recommendations during the course of this investigation, considerable safety action has been taken by various regulatory authorities, airlines, and manufacturers to address the recommendations, advisories, and observations made by the Board. Such action taken has significantly improved aviation safety worldwide.
Safety action taken to date includes the following:
● MPET-covered thermal acoustic insulation blankets have been ordered removed from aircraft;
● new flammability testing criteria have been developed;
● flight crew reading lights have been re-designed;
● additional guidance material for dealing with smoke situations has been issued to flight crews;
● aircraft checklists have been modified;
● numerous inspections have been completed on wiring and components to look for and eliminate potential ignition sources;
● the IFEN system was removed voluntarily from Swissair aircraft; subsequently the design was de-certified; and
● new FAA policies are in place for the certification of in-flight entertainment systems.
So there you have it, an inflight electrical fire that resulted in the crash of SwissAir Flight 111 with the loss of 229 lives. Better flammability testing criteria, in-flight fire detection, flight crew reading lights, and checklist redesign could have prevented a tragedy that took 229 lives.
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