Tuesday, May 12, 2009
Should You Reset A Circuit Breaker?
Revisiting and revising old ways of doing things
|The NTSB says it’s time to rethink something most GA pilots learned early in their training: If a circuit breaker trips while you’re flying, it’s okay to reset it after allowing a minute or two for it to cool, even if you have no idea what caused it to trip and cut off electrical power to a particular circuit. |
A day before the accident, there was a burning smell after the weather radar malfunctioned while the airplane was in flight. The pilot on that flight turned off the weather radar and manually pulled the related circuit breaker, cutting power to the system. The burning smell subsequently “went away,” according to the pilot’s entry in the plane’s maintenance discrepancy binder, and the pilot flew the plane for more than an hour without further incident. The NTSB said that the radar problem could have developed into a significant in-flight smoke and fire event had the pilot not shut down the radar and pulled the circuit breaker.
According to regulations, GA operations may operate piston-powered airplanes such as the Cessna 310 with noncritical inoperative equipment if the inoperative item isn’t required for flight and is either: 1) removed from the airplane (with the cockpit control placarded and the maintenance recorded), or 2) deactivated and placarded as inoperative. Further, federal regulations state that an appropriately rated pilot or mechanic must determine that the inoperative equipment doesn’t constitute a hazard to flight.
Interviews indicated that NASCAR’s aviation director, maintenance director and chief pilot discussed the weather radar discrepancy the day before the accident, but no one examined the plane. The NTSB concluded that without examining the weather radar system and then either removing the plane from service or placarding it and collaring the circuit breaker so it couldn’t be pushed in (as well as making a maintenance records entry), it wasn’t permissible to fly the airplane under federal regulations.
The NTSB noted that both pilots on the accident flight had access to information that could have alerted them to the unresolved maintenance discrepancy and led them to take appropriate action. The NTSB theorized that one of the pilots may have reset the circuit breaker before or after takeoff. The impact and fire damage to the airplane, however, prevented physical confirmation that the circuit breaker was reset. The plane was airborne for 10 minutes before the pilots reported a problem; it crashed two minutes later.
Although the weather radar system and its wiring were the most likely source of the in-flight fire, there was insufficient evidence to conclusively determine the fire’s origin. The NTSB noted that GA pilots often reset circuit breakers during preflight preparations unless the circuit breakers are placarded or collared to show that the associated system is to remain unpowered. Further, the accident plane’s “Before Starting Engines” checklist included an item stating, “Circuit Breakers—IN.” The NTSB concluded that it’s likely one of the pilots, consistent with routine and/or the aforementioned checklist, reset the weather radar circuit breaker, which restored electrical power to the weather radar system’s wiring and resulted in the in-flight fire.
After the accident, NASCAR’s corporate aviation division made several revisions to its standard operating procedures, including the requirement that an “In Maintenance” placard be placed near an airplane’s entrance during maintenance. The revised procedures also require maintenance and flight crew personnel to meet face-to-face before each flight to discuss the airplane’s airworthiness.
The NTSB determined that the probable causes of this accident were the actions and decisions by NASCAR’s corporate aviation division’s management and maintenance personnel to allow the accident airplane to be released for flight with a known and unresolved discrepancy, and the accident pilots’ decision to operate the airplane with that known discrepancy, a discrepancy that likely resulted in an in-flight fire.
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