US investigators are urging the FAA to pass long-delayed directives to fit redesigned windshield-heating systems on Boeing aircraft after the latest in a series of smoke and fire incidents resulted in an American Airlines Boeing 757 windshield’s shattering in flight.
The National Transportation Safety Board (NTSB) has reiterated recommendations – some of which date back nearly four years – to install redesigned electrical terminals in the windshield-heating system on Boeing 747, 757, 767 and 777 jets.
It follows the emergency diversion of an American Airlines 757, operating the San Juan-Philadelphia route on 30 January, to Florida’s West Palm Beach after smoke from the first officer’s windshield heater filled the cockpit.
The pilots put on oxygen masks and smoke goggles. During the descent to Palm Beach Airport the inner pane of the first officer’s windshield shattered, although the fragments remained in place. The aircraft landed safely but some of the 146 occupants were treated in hospital for smoke inhalation.
This incident has highlighted the NTSB’s frustration with the FAA over the windshield-heater design. Five other similar incidents on 757s were reported between 2004 and 2006 and, during the investigation into the earliest of these, Boeing stated that at least four similar incidents had previously occurred on 747, 757, 767 and 777 aircraft.
Analysis has identified inadvertent cross-threading of the screw attaching power wires to the heating terminal as a cause of electrical arcing. In 2004 Boeing developed a modification to the terminal – a pin-and-socket connector to replace the screw – and the NTSB says the FAA agreed to issue a corresponding airworthiness directive.
But delays to finalising approval for the related service bulletins held up the process. Boeing eventually released service bulletins for the 747, 757 and 777 in mid-2006, but a service bulletin for the 767 has continued to be delayed.
Last September the NTSB told the FAA it was “very concerned” that airworthiness directives for the modifications, originally scheduled for issue two years previously, had still not been issued.
It urged the FAA to complete the process of approving the service bulletin for installations on 767s, and to issue airworthiness directives to carry out the corresponding installation on all 747, 757, 767 and 777 aircraft. As a result of the latest American 757 incident, the NTSB has reiterated its frustration, stating: “These safety recommendations have yet to be implemented by the FAA.”
Source: lightglobal.com's sister premium news site Air Transport Intelligence news