Discussion

CASE STUDY SWISSAIR FLIGHT 111 ACCIDENT – SEARCHING FOR ANSWERS SCATTERED ACROSS THE OCEAN FLOOR The Accident On 2 September 1998, Swissair flight 111 (SR 111) left New York in the United States headed for Geneva, Switzerland. The aircraft was a McDonnell Douglas MD-11 with 215 passengers and 14 crew members on board. Approximately one hour into the flight, the crew noticed a strange smell in the cockpit, which quickly dissipated. The crew decided the air conditioning system was responsible and contacted the Moncton area control centre (ACC) requesting routing to land at a convenient airport. The pilots requested Boston airport – about 300 nautical miles behind them – but after a suggestion from the controller, headed towards Halifax which was only 56 nautical miles from their current location. The crew put on their oxygen masks. Minutes later, SR 111 was 30 nautical miles from the runway of Halifax Stanfield International Airport when the pilots informed the controller they needed more time to prepare for landing, so the controller instructed SR 111 to turn to a heading of 360 degrees to provide a longer routing for the aircraft to lose altitude. The pilots discussed dumping fuel to reduce the aircraft’s weight for landing, and both agreed they had time to do so. Seconds later, both pilots declared an emergency. They stated that they had begun dumping fuel and had to land immediately. SR 111 declared an emergency again and the controller responded with clearance to dump fuel, but there was no further response from the crew. Observers in the area of St. Margaret’s Bay, Nova Scotia, witnessed a large aircraft fly low overhead and described a loud ‘clap’. Although SAR teams looked through the night, no survivors were found. The aircraft had impacted the ocean and was destroyed. The Investigation As the accident took place in Canadian waters, Canada’s Transportation Safety Board (TSB) was responsible for leading the investigation. The TSB had one clue to kick-start the investigation: the crew had told the controller they smelled smoke, which suggested an on-board fire. The investigatory benefit of the aircraft striking water is that the water immediately doused any flames and preserved the state of the wreckage – there was no post-crash fire to destroy evidence. Yet this benefit was countered by the wreckage being scattered across the ocean floor at a depth of 55 meters (180 feet). Although divers recovered the FDR and the CVR, it was discovered that both recorders ceased functioning immediately after the pilots declared an emergency (significantly complicating the investigation). The final six minutes of the flight were lost. This led to an intense 13-month salvage operation that involved more than 4000 people. Ships, including the Queen of the Netherlands, which vacuums the ocean floor, combed the seabed and collected everything from tangled wires and cloth to metal scraps. Tragically, only one of the 229 victims could be identified visually, requiring the expertise of a team of medical examiners. This team included a pathologist and assistant, nurse, Royal Canadian Mounted Police, photographer, dentist, radiologist, X-ray technician, fingerprint technician, and DNA specialists. In total 1370 DNA samples were processed and all 229 victims were identified. The cost of the medical and dental detective work was CAD$800 000, but a

greater cost may have been the emotional impact – these professionals later spoke out about the profound, yet intangible, emotional effect this event had on their lives. Investigators salvaged 98 per cent of the aircraft (by weight) from the ocean. Every item needed to be examined for clues and added to a physical and digital mock-up of the aircraft. A full-size metal frame was constructed, allowing investigators to place identified pieces on the mock aircraft (much like piecing together a jigsaw puzzle). Simultaneously, a digital model was created to rebuild the aircraft electronically. This process allowed investigators to make several key discoveries: ● carpet pieces revealed melted plastic ‘drip’ marks, indicating that an intense heat in the aircraft attic area had melted the ceiling; ● a charred galley roof; and ● burnt ducts within the overhead attic area above the cockpit. This narrowed the investigation to the hidden attic area above the cockpit and front galley. A prime suspect was the wiring that runs throughout this area. Over time, with the vibration of flight, wires can develop cracks in their plastic insulation. Experts estimate between 400 and 1500 wire insulation cracks exist per aircraft, depending on the aircraft’s age. These cracks can allow electrical current to ‘jump’ to other wires or the aircraft itself if the wire crack comes into contact with water (such as from condensation). Electrical jumping is called arcing and produces an intense heat of around 6600 degrees Celsius (12 000 degrees Fahrenheit). Wiring for the in- flight entertainment network (IFEN) became a suspect as many arcs were found on IFEN wires. Investigators eventually tracked the ignition point down to a few inches. The electrical arc may have sparked the fire, but what fueled the flames? The attic area is lined with metallized polyethylene terephthalate (MPET)-covered insulation blankets, which had passed FAA testing and were deemed fireproof. Therefore, TSB investigators were surprised when they salvaged insulation blankets with burn marks. Though insulation is supposed to be fireproof, it quickly caught fire when the FAA retested it as part of the investigation. The FAA also tested end caps of the ventilation system, which were also supposed to be fireproof, and when tested found that they also quickly caught fire. With the end caps burnt away, oxygen flowed freely and fed the flames. When it was discovered that the fireproof materials had fueled a fire, the TSB released preliminarily recommendations that these flammable components be removed and replaced in the global fleet in the interest of safety. This was a case where it was clearly necessary to release preliminary recommendations, rather than waiting for the final report when the investigation was complete. Probable Cause From the time of the accident until the completion of the final report, the investigation took four years and cost nearly CAD$40 million. Based on the TSB investigation, the chain of events that led up to the accident was as follows: Condensation caused a cracked IFEN wire to arc within the hidden attic area above the cockpit. The arc ignited the MPET-covered insulation blankets, which fueled the fire and led to the pilots noticing a whiff of smoke before it was sucked away by recirculation fans. As the pilots didn’t know the fire was raging above their heads they didn’t consider the event an immediate threat and delayed landing to dump fuel. While completing a checklist, the Captain turned off non-essential power, which stopped the recirculation fans. This caused the fire to be

drawn towards the cockpit. The flight recorders recorded a rapid succession of system failures as fire burnt through wires, leading to the autopilot disengaging and causing the CVR and FDR to stop recording (losing the final six minutes of the flight). The plastic cockpit ceiling began to melt and drip down on the pilots. Both pilots declared an emergency. The Captain got out of his seat to fight the fire while the FO piloted the aircraft. The glass cockpit instruments stopped working, and smoke and fire obscured standby instruments, forcing the FO to fly by visual reference (i.e., looking out the window). With a dark sky above and black water below, there was very little visual reference. The aircraft crashed into the ocean five nautical miles southwest of Peggy’s Cove, Nova Scotia. Recommendations The TSB made 23 recommendations associated with the SR 111 accident. Among other things, the TSB ● identified the risk of wiring becoming cracked; ● suggested that CVRs and FDRs be outfitted with longer duration recordings and their own power supply; ● determined that insulation materials (MPET-covered insulation blankets) were flammable and should be replaced, and that more rigorous flammability test criteria be developed; ● suggested improved firefighting measures (including smoke and fire detection and suppression systems); and ● advised that it should be industry standard for aircraft to land expeditiously anytime smoke is noticed from an unknown source.