Date:30 September 2007
How crashes spurred new technology that keeps air travel routine
As Aloha Flight 243, a weary 19-yearold Boeing 737 on a short hop from Hilo, Hawaii, to Honolulu, levelled off at 7 500 m, a large section of its fuselage blew off, leaving dozens of passengers riding in the open-air breeze. Miraculously, the rest of the plane held together long enough for the pilots to land safely. Only one person, a flight attendant who was swept out of the plane, was killed.
The National Transportation Safety Board (NTSB) blamed a combination of corrosion and widespread fatigue damage, the result of repeated pressurisation cycles during the plane’s 89 000-plus flights. In response, the FAA began the National Ageing Aircraft Research Program in 1991, which tightened inspection and maintenance requirements for high-use and high-cycle aircraft. Post-Aloha, there has been only one American fatigue-related jet accident – the Sioux City DC-10.
When USAir Flight 427 – a Boeing 737 – began its approach to land at Pittsburgh, it suddenly rolled to the left and plunged 1 500 m to the ground, killing all 132 on board. The plane’s black box revealed that the rudder had abruptly moved to the full-left position, triggering the roll. But why? USAir blamed the plane. Boeing blamed the crew. It took nearly five years for the NTSB to conclude that a jammed valve in the rudder-control system had caused the rudder to reverse: As the pilots frantically pressed on the right rudder pedal, the rudder went left.
As a result, Boeing spent R3,5 billion to retrofit all 2 800 of the world’s most popular jetliner. And, in response to conflicts between the airline and the victims’ families, the US Congress passed the Aviation Disaster Family Assistance Act, which transferred survivor services to the NTSB.
Fire prevention in the hold
Although the FAA took anti-cabin-fire measures after the 1983 Air Canada accident, it did nothing to protect passenger jet cargo compartments – despite NTSB warnings after a 1988 cargo fire in which the plane managed to land safely. It took the horrific crash of ValuJet 592 into the Everglades near Miami to finally spur the agency to action.
The fire in the DC-9 was caused by chemical oxygen generators that had been illegally packaged by SabreTech, the airline’s maintenance contractor. A bump apparently set one off, and the resulting heat started a fire, which was fed by the oxygen being given off. The pilots were unable to land the burning plane in time, and 110 people died. The FAA responded by mandating smoke detectors and automatic fire extinguishers in the cargo holds of all commercial airliners. It also bolstered rules against carrying hazardous cargo on aircraft.
Electrical spark elimination
It was everybody’s nightmare: a plane that blew up in midair for no apparent reason. The explosion of TWA Flight 800, a Boeing 747 that had just taken off from JFK bound for Paris, killed all 230 people aboard and stirred great controversy. After painstakingly reassembling the wreckage, the NTSB dismissed the possibility of a terrorist bomb or missile attack and concluded that fumes in the plane’s nearly empty centre-wing fuel tank had ignited, most likely after a short circuit in a wire bundle led to a spark in the fuel gauge sensor.
The FAA has since mandated changes to reduce sparks from faulty wiring and other sources. Boeing, meanwhile, has developed a fuel-inerting system that injects nitrogen gas into fuel tanks to reduce the chance of explosions. It will install the system in all its newly built planes, starting in 2008. Retrofit kits for in-service Boeings will also be available.
About an hour after takeoff, the pilots of Swissair’s Flight 111 from New York to Geneva – a McDonnell Douglas MD-11 – smelled smoke in the cockpit. Four minutes later, they began an immediate