Fire Hazard in Resetting Circuit Breakers SAIB CE-10-11

This Special Airworthiness Information Bulletin (SAIB) advises pilots, owners, maintenance personnel, and operators of an airworthiness concern on all 14 CFR, part 23/Civil Air Regulations (CAR 3) airplanes. It gives best practices regarding tripped circuit breakers (C/B), inspection and maintenance of systems, and aging wires. There is a potential hazard when resetting an opened circuit breaker.
At this time, this airworthiness concern is not considered an unsafe condition that would warrant an airworthiness directive action under Title 14 of the Code of Federal Regulations (14 CFR), part 39.
 

Background
On a flight in the accident airplane, the day before an accident, a pilot had a weather radar failure and a burning smell in the airplane. In response, 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 National Transportation Safety Board (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, we do not know if the circuit breaker tripped again but, if it did, it was after an uncontrollable fire was started.

SAIB Attached