The year of 2018 was yet again another substantial year in commercial air travel. The first quarter of 2018 saw commercial flights carry over 202 million passengers in the US, approximately 8 million more than in the first quarter of 2017. Air travel remains increasingly popular, accessible to the public, and statistically the safest way to travel. This level of safety has been earned through decades of groundbreaking innovation, sometimes undeniably spurred by the desire to avoid repeating past tragedy.
An impactful and memorable incident that caused the industry to reevaluate its processes and procedures was the crash of Swissair Flight 111. Occurring almost two years after the Trans World Airlines Flight 800 (TWA800), the Swissair Flight 111 and TWA800 shared a common issue: wiring system failure.
The Background
On September 2nd, 1998, Swissair Flight 111 departed from New York’s J.F.K. airport at 8:18 p.m. The seven-year-old MD-11 aircraft was bound for Geneva carrying 215 passengers and 14 crew members. About 53 minutes after departure, the flight crew detected an abnormal odor in the cockpit. Initially dismissing it as a minor air conditioning problem, they quickly assessed that in fact it was smoke, and radioed air traffic control at 9:14pm declaring an issue. Originally turning back towards Boston, upon recommendation by air traffic control they diverted towards the closer Halifax International Airport in Nova Scotia and began landing procedures.
The crash investigation found evidence of arcing wires. Source NASA.
About 13 minutes after the initial detection of smoke, the aircraft’s flight data recorder began to record a cascade of system failures. The flight crew then officially declared an emergency with the need to land immediately. One minute later, radio communications and secondary radar contact with the aircraft were lost, and the flight recorders ceased functioning. At 9:31pm, the aircraft crashed into the ocean about five nautical miles southwest of Peggy’s Cove, Nova Scotia, Canada. There were no survivors. The official report here.
The Recover Operation
The recovery of the remains of the aircraft and passengers began almost immediately and proved to be a harrowing task; the plane had hit the water at a high speed and the wreck was 180 feet below the waters of the Atlantic. Eventually, more than 4,000 people recovered about two million pieces of wreckage. Although the flight recorders proved to be a dead end since they stopped working six minutes after the pilots radioed emergency, the investigators quickly turned to the wreckage itself, as it was clear an onboard fire was the culprit.
The intense burn marks on pieces of debris reflected the heat intensity of the flames at various points in the aircraft, and the hottest temperatures of over 1,000oF were exclusively in the front of the plane. An extensive investigation concluded that the fire started when a damaged wire produced an arcing event — a phenomenon in which a wire’s damaged insulation leads to sparking — in the plane’s improperly installed new entertainment system that ignited a flammable insulation in the overhead of the cockpit.
The investigation of SwissAir111 found the new entertainment system was connected to the emergency power bus. When load shedding began, power could not be removed from this system. Source TSB.
Investigation and Impact
The investigation of the Swissair Flight 111 crash has had a resounding impact on aviation safety for the hundreds of millions of travelers around the world. Twenty of the 23 Transportation Safety Board recommendations have resulted in major safety actions (many of these captured in the 25.1700 series of regulations that elevated wiring to a system). The flammable materials that were ignited in the attic fire, such as metallized polyethylene terephthalate (MPET), are no longer used in aircraft in order reduce the risk of fires. In addition, much more rigorous flammability testing and standards have been introduced in order to certify thermal insulation materials before usage.
The loss of the Swissair 111 flight was one more incident adding to the case against the use of polyimide insulation for aircraft wiring such as MIL-W-81381 constructions (other constructions such as AS22759/80 – /92 were deemed acceptable); new standards to separate and protect insulation materials from abrasion have emerged in order to increase resistance to arcing damage.
The FAA also began conducting a rigorous test program to evaluate arc fault mitigation in products like circuit breakers, new wire/cable insulation, and thermal acoustical blanket material. Despite the disastrous loss of life from a single event, the immense, invaluable knowledge and change that occurred from such an incident has improved commercial air safety for decades to come.
Devon Gonteski
Engineer, Lectromec
devon.gonteski@lectromec.comDevon has been with Lectromec since 2017 and has been a key contributor on projects involving wire degradation assessment and wire/cable certification testing. Her skills in Lectromec’s lab ensure regular delivery of accurate test results across multiple disciplines.