SR 111 Investigation Report
3.3 Other Findings
- The Royal Canadian Mounted Police found no evidence to support the involvement of any explosive or incendiary device, or other criminal act in the initiation of the in-flight fire.
- The 13-minute gap in very-high frequency communications was most likely the result of an incorrect frequency selection by the pilots.
- The pilots made a timely decision to divert to the Halifax International Airport. Based on the limited cues available, they believed that although a diversion was necessary, the threat to the aircraft was not sufficient to warrant the declaration of an emergency or to initiate an emergency descent profile.
- The flight crew were trained to dump fuel without restrictions and to land the aircraft in an overweight condition in an emergency situation, if required.
- From any point along the Swissair Flight 111 flight path after the initial odour in the cockpit, the time required to complete an approach and landing to the Halifax International Airport would have exceeded the time available before the fire-related conditions in the aircraft cockpit would have precluded a safe landing.
- Air conditioning anomalies have typically been viewed by regulators, manufacturers, operators, and pilots as not posing a significant and immediate threat to the safety of the aircraft that would require an immediate landing.
- 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 being unaware that an on-board fire was propagating.
- Air traffic controllers were not trained on the general operating characteristics of aircraft during emergency or abnormal situations, such as fuel dumping.
- Interactions between the pilots and the controllers did not affect the outcome of the occurrence.
- The first officer's seat was occupied at the time of impact. It could not be determined whether the captain's seat was occupied at the time of impact.
- The pilots shut down Engine 2 during the final stages of the flight. No confirmed reason for the shutdown could be established; however, it is possible that the pilots were reacting to the illumination of the engine fire handle and FUEL switch emergency lights. There was fire damage in the vicinity of a wire that, if shorted to ground, would have illuminated these lights.
- When the aircraft struck the water, the electrically driven standby attitude indicator gyro was still operating at a high speed; however, the instrument was no longer receiving electrical power. It is unknown whether the information displayed at the time of impact was indicative of the aircraft attitude.
- Coordination between the pilots and the cabin crew was consistent with company procedures and training. Crew communications reflected that the situation was not being categorized as an emergency until about six minutes prior to the crash; however, soon after the descent to Halifax had started, rapid cabin preparations for an imminent landing were underway.
- No smoke was reported in the cabin by the cabin crew at any time prior to CVR stoppage; however, it is likely that some smoke would have been present in the passenger cabin during the final few minutes of the flight. No significant heat damage or soot build-up was noted in the passenger seating areas, which is consistent with the fire being concentrated above the cabin ceiling.
- No determination could be made about the occupancy of any of the individual passenger seats. Passenger oxygen masks were stowed at the time of impact, which is consistent with standard practice for an in-flight fire.
- No technically feasible link was found between known electromagnetic interference/high-intensity radiated fields and any electrical discharge event leading to the ignition of the aircraft's flammable materials.
- Regulations did not require the recording of cockpit images, although it is technically feasible to do so in a crash-protected manner. Confirmation of information, such as flight instrument indications, switch position status, and aircraft system degradation, could not be completed without such information.
- Portions of the CVR recording captured by the cockpit area microphone were difficult to decipher. When pilots use boom microphones, deciphering internal cockpit CVR communications becomes significantly easier; however, the use of boom microphones is not required by regulation for all phases of flight. Nor is it common practice for pilots to wear boom microphones at cruise altitude.
- Indications of localized overheating were found on cabin ceiling material around overhead aisle and emergency light fixtures. It was determined that the overhead aisle and emergency light fixtures installed in the accident aircraft did not initiate the fire; however, their design created some heat-related material degradation that was mostly confined to the internal area of the fixtures adjacent to the bulbs.
- At the time of this occurrence, there was no requirement within the aviation industry to record and report wiring discrepancies as a separate and distinct category to facilitate meaningful trend analysis in an effort to identify unsafe conditions associated with wiring anomalies.