The captain of a United Airlines Boeing 757-200 that was cruising at 36,000ft (10,973m) en route from New York JFK airport to Los Angeles the night of 16 May had to use a second halon fire extinguisher, brought forward by cabin crew, to douse a fire in the aircraft's lower front windshield.
Earlier the captain put out the fire with a halon extinguisher located in the cockpit but the fire then reignited, according to the US National Transportation Safety Board (NTSB), which issued an update on the incident today. The fire did not reignite after the second bottle was discharged.
Both the captain and first officer had earlier donned oxygen masks and smoke goggles after smelling a "strong acrid smell" and observing smoke coming from the windshield, says NTSB.
The pilots declared an emergency and initially were being given vectors to land at the closest airport, which turned out to be Harrisburg International airport in Pennsylvania, according to air traffic control conversations captured by the website LiveATC.net.
The crew later noted that the fire "was under control now" and requested to be diverted to the Dulles International airport in Virginia, a hub location for the airline.
The crew advised controllers that no airport rescue and fire fighting equipment would be needed for their landing, though fire crews later did meet the aircraft on the runway and board the cabin.
The NTSB notes that the captain's windshield cracked at approximately 500ft mean sea level (MSL) altitude during the landing, There was no evacuation or injuries to any of the 105 passengers or seven crew members after the uneventful landing.
NTSB says a preliminary examination of the cockpit area revealed that the inner pane of the captain's windshield had cracked and that one of the five terminal blocks attached to the inside lower left windshield "was consumed by fire", with associated damage to a wire harness.
The agency notes that two previous windshield fire events on Boeing 757-200s had prompted it in 2007 to issue a safety recommendation to the US FAA to require operators to replace the windshield heat terminal blocks on Boeing 747,757, 767 and 777 aircraft with a new design.
The FAA issued a proposed airworthiness directive (AD) to address the problem in March 2008, but has not yet finalised the action. An FAA spokeswoman says the AD was to be finalised in August, but the action will now be accelerated and issued "as soon as possible".