The National Transportation Safety Board is urging the FAA to issue an emergency airworthiness directive requiring operators of certain Piper Aircraft PA-31T, PA-31T1, PA-31T2, PA-31T3, and PA-31P-350 Navajos to address a wiring condition at the floor-mounted circuit breaker panel that could lead to chafing, thermal stress, or arcing directly below the panel.
In a Jan. 9 letter to the FAA, the NTSB issued an urgent safety recommendation for stronger measures than a special airworthiness information bulletin (SAIB) the FAA issued in December to alert operators about the problem.
The SAIB, noting that reviews of the condition were continuing, listed several inspection and repair steps recommended to be taken at the next scheduled maintenance visit, and thereafter at annual inspections, as well as a functional test on any electrical systems disturbed during any inspection.
The NTSB’s urgent recommendation to make those steps mandatory was “based upon preliminary findings in the ongoing investigation of the July 29, 2016, in-flight breakup of a Piper PA-31T medical transport flight in California.”
Evidence indicated that an in-flight fire “occurred in the area where these electrical wires and adjacent hydraulic lines may have been in contact,” the NTSB wrote.
Current maintenance procedures for a general visual inspection “do not provide adequate guidance for inspection in the area of the floor-mounted circuit breaker panel because of its location and the confined space in that area. Thus, contact between electrical wires and hydraulic fluid lines can persist undetected,” the letter said, noting that in six other PA-31T series airplanes examined, electrical and hydraulic lines were found to be in contact "in all six cases."
The NTSB requested that the FAA respond to its recommendation within 30 days. NTSB urgent safety recommendations are issued during investigations “when the Board believes an imminent threat to life and safety exists, based upon findings of the ongoing investigation.”