Clues Point Toward Fire

The cause of the accident still has not been determined, but investigators believe there may have been an electrical fire near the cockpit that spread in the plane’s insulation.
     The FAA has ordered airlines to replace the type of insulation used aboard the plane, blankets covered with metalized Mylar, over the next four years.
     The safety board is participating in the investigation but its letter did not specifically refer to the Swissair crash. Instead, it focused on three other incidents:

     In November 1998, a fire erupted in a Delta Air Lines MD-11 while the plane was still parked at the gate. Investigators found wiring damage in the cargo control unit, which led to excessive electrical current when it was turned on. That trigged the release of hot gases, which ignited a nearby insulation blanket coated with Mylar.

     In March 1999, maintenance workers found evidence of a fire after they pulled up floorboards on a World Airways MD-11. The fire was blamed on chafing caused after a wire bundle was not properly restrained, but investigators found that the cargo control unit had not been replaced and it displayed evidence of the same problems found in the Delta Air Lines unit.

     In September 1998, the same month as the Swissair crash, the control unit in a Varig Airlines MD-11 was damaged while the airplane was parked. According to Lucas, there was evidence of melting in upgraded electrical pins that had been installed after problems were detected with the original pins.

Fire Risk Even on Ground
“The safety board is also concerned about the risks of a CCU-related fire during passenger loading and unloading, and that a ground fire could propagate without detection until an airplane is airborne,” Hall wrote to FAA Administrator Jane Garvey.
     Both Boeing, which bought McDonnell Douglas, the designer of the MD-11, and Lucas Aerospace Cargo Systems, which manufactures the control unit, have recommended or are preparing to recommended similar repairs.
     The FAA typically takes time to review a board recommendation, but in the vast majority of cases, the agency accepts it.
     Swissair Flight 111, an MD-11 bound from New York to Geneva, crashed in September 1998 off the coast of Nova Scotia 16 minutes after the pilots reported smoke in the cockpit. All 229 aboard were killed.