FAA Issues SAIB on Circuit Breakers
A few years ago, the FAA and Wichita State University undertook a study concerning aging aircraft and how various systems and components deteriorated over time. One of the things that came to light during this effort was the revelation that circuit breakers were prone to failure if they were not regularly exercised. Testing of the circuit breakers removed from a well-used Cessna 421 showed that some failed to trip properly when initially tested. When they were cycled (pulled out and then reset), they began to trip at the proper amperage after many of the breakers regained proper function from being cycled a number of times. At the very least, each resettable circuit breaker should be cycled a few times during the aircraft’s annual inspection. This type of inspection will be part of the new ASTM specification concerning aircraft wiring, ASTM F39.
In a similar vein, the FAA has recently published SAIB CE-10-11R1, January 14, 2010. It gives both maintenance and operational personnel guidance concerning tripped circuit breakers, aging wiring, and system maintenance. Recognizing that many pilot handbooks for older aircraft (indeed, if one even exists) don’t have procedures for resetting circuit breakers, the SAIB also gives recommended procedures for dealing with circuit breakers.
You can download a copy of the SAIB from the FAA Regulatory Guidance Library here.