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.