Aviation News Item: 03429

23rd Dec 2009

Source: aero-news.net

One Aircraft Went Down Following An Apparent Electrical Malfunction, Fire
The FAA his issued a Special Airworthiness Information Bulletin (SAIB) concerning circuit breakers in older GA aircraft. A fire hazard exists following circuit breaker resets.

The case cited involves a pilot who had a weather radar failure and a burning smell in the airplane the day prior to the accident. The pilot turned off the weather radar and manually pulled the related circuit breaker. The burning smell went away according to the pilot's entry in the airplane's maintenance discrepancy binder. The pilot continued the flight with the circuit breaker pulled for another hour.

The next day it is likely the pilots reset the weather radar C/B, restoring power to the weather radar system wiring. This is consistent with routine or the "Before Starting Engines" checklist. Then 10 minutes after takeoff, they announced a problem and crashed about two minutes later. The NTSB determined that the most likely failure was from the weather radar and its associated wiring, which would be possible only if that crew reset the weather radar circuit breaker.

Current guidance for part 25, Transport Airplanes in AC 25-16, Electrical Fault and Fire Prevention and Protection that has been accepted for small airplanes, is to recommend that no pilot should reset any circuit breaker more than once. In the accident airplane, the FAA does not know if the circuit breaker tripped again but, if it did, it was after an uncontrollable fire was started.

The FAA says that the C/Bs that are essential for safety in flight are required to be located and marked so they can be reset in flight. The rules do not require segregation of non-essential C/Bs. This SAIB references the most current "best practices" for circuit breakers, the electrical system and aging wiring. It is important to note that many older aircraft may have little or no guidance on resetting policy in their airplane flight manuals.

The FAA recommends that pilots and owners mark those breakers that are essential for safety in flight. "Essential" C/Bs should be reset in flight only once after at least one minute, if there is no remaining smoke or "burning smell" and the affected system and equipment is needed for the operational environment.

FAA says any non-essential C/Bs should not be re-set in flight. Preflight checklists should be revised delete "Circuit breakers-In", if applicable, and insert: "Check circuit breakers and if a circuit breaker is not set, do not reset the circuit breaker if there is a related maintenance malfunction."

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