A cockpit fire that forced a United Airlines flight to make an emergency landing was concentrated in a piece of window-heating equipment that was the subject of a safety warning three years ago, accident investigators said Friday.
The National Transportation Safety Board said in a statement that two fire extinguishers were required to put out the fire aboard Flight 27 last Sunday night. The Boeing 757 was en route from New York to Los Angeles at about 36,000 feet when the fire broke out, forcing a landing at Dulles International Airport in Virginia. None of the 105 passengers and seven crew members was injured.
Passengers said they could see flames when the captain opened the cockpit door to request a flight attendant retrieve a fire extinguisher.
The captain first used a halon fire extinguisher in the cockpit to put out the fire, the board said. However, the fire reignited and a second extinguisher was required, the board said.
The fire consumed one of the five terminal blocks - a connection between power wires and heating elements - attached to the window on the captain's side of the cockpit, the board said. The left side of the cockpit also suffered significant soot and peeling paint, the board said.
The inside of the captain's window cracked as the plane was landing, the board said. The window has been removed from the plane for examination, the board said.
A combination of intense heat inside and extreme cold outside can cause window cracking. The possibility that a window might shatter in flight is a significant safety concern.
The Federal Aviation Administration and Boeing were aware as far back as 2004 that a loose connection between the power wires and the windshield heating elements in the 757 had been the source of at least six incidents, including cockpit fires, smoke and electrical arcing, according to a letter NTSB sent FAA three years ago. Boeing officials said this week that they are aware of 29 incidents over eight years.
NTSB recommended in the letter that FAA require airlines to replace the terminal blocks on the 757 - one of the most widely used airliners in U.S. - as well as on the 747, 767 and 777.
In March 2008, FAA proposed giving airlines a choice of conducting repeated inspections of the window heating systems or replacing the terminal block. The proposed order hasn't been made final. FAA officials said earlier this week that they are expediting work on the safety order.
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