Clamps improperly installed during maintenance visits have been tied to at least three serious in-service fire and smoke incidents on Boeing 737 Classics, prompting the FAA to warn operators and encourage compliance with a Boeing-suggested fix.
The FAA’s Safety Alert for Operators, approved earlier this month and released this week, says that 279 737 Classics inspected in 2010-2012 turned up 71 incidents of improperly oriented flight deck ceiling/side panel gasper air duct hose thumb clamps.
The three most serious incidents caused chafing, arcing, smoke, and a fire that damaged more than 50 wires, FAA reports. One of the incidents occurred in flight; the other two were on aircraft parked at gates.
This new alert suggests that part of the problem is design-related. The clamp is difficult to tighten when installed in the correct orientation, the agency explains. Flipping the clamp 180 deg. makes it “much easier to install,” the agency notes.
Unfortunately, that also creates the hazard scenario most likely to trigger these incidents.
In late April, Boeing issued a service bulletin recommending operators replace metal clamps with plastic ties at the next maintenance visit.
The FAA suggests that operators follow the bulletin and warn mechanics and maintenance providers of the problem.