Says Cross-Threading May Result In Smoke, Fire In The Cockpit

In response to numerous reports of fires near the windshields of several Boeing aircraft over the past three years, on Wednesday the National Transportation Safety Board issued two safety recommendations calling for operators of Boeing 747, 757, 767, and 777 aircraft.

In its recommendations to the FAA, the Board said the agency should a) complete the process begun in 2004 to approve the service bulletin for the installation of the redesigned windshield heat terminal block on Boeing 767 airplanes (A-07-49); and issue airworthiness directives to replace the windshield heat terminal block on all Boeing 747, 757, 767, and 777 airplanes in accordance with the Boeing service bulletins.

"On January 25, 2004, American Airlines flight 1477, a 757-200 airplane, declared an emergency on departure from the Dallas-Fort Worth International Airport (DFW) because of smoke and fire near the windshield heat terminal. The airplane returned to DFW and landed safely," the NTSB states. "Four days earlier, on January 21, 2004, the Danish Aircraft Accident Investigation Board notified the National Transportation Safety Board of a similar incident in which an electrical fire started near the windshield heat terminal on an Air Greenland 757-200 (OY-GRL) airplane in Copenhagen, Denmark. The event occurred on the ground while the airplane was being readied for flight.

"The windshields from both incident airplanes were removed and shipped to the windshield manufacturer, PPG, Inc., where a teardown examination was accomplished in March 2004 under the supervision of a Safety Board investigator, with representatives from the Federal Aviation Administration (FAA), Boeing, and American Airlines. The examination revealed the cause of the fires to be the cross-threading of the screw that attached the power wire to the windshield heat terminal block, which resulted in an electrical arc and fire.

"Board investigators determined that the windshield from the January 25, 2004, incident was not the original one installed by Boeing; the windshield was installed in 1998. Investigators were unable to determine if any recent maintenance work on the windshield could have caused the cross-thread condition."

The NTSB also noted three more related incidents, all involving 757s, that occurred before Boeing issued SBs for additional airplane models. Those incidents were also traced to cross-thread issues with the windshield heat terminal block.

FMI: Read The NTSB Recommendations (.pdf)