On February 26, 1994, a British Aerospace ATP (registration N854AW) operated by United Feeder Service was involved in an aviation accident near Mosinee, WI. Investigators recorded the probable cause as: the inadequate design of the PBSI electrical switch(es), and the operator's failure to expeditiously implement corrective Service Bulletins. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive; 1 related events involving the same aircraft type or operator are linked below.
Flight crew encountered smoke in the cockpit during descent, traced to a red-hot push button selector indicator switch. The copilot discharged a fire extinguisher, stopping the smoke. Maintenance found the switch scorched and melted, with heat damage to adjacent wiring.
Incident Overview
While descending from cruise altitude, the flight crew observed smoke in the cockpit and declared an emergency. The copilot identified the source as a red-hot push button selector indicator (PBSI) switch for the flight idle baulk test. The copilot discharged a portable fire extinguisher onto the switch, after which the smoke ceased.
Maintenance Findings
Following the incident, maintenance personnel removed the PBSI switch. Examination revealed the switch was scorched and melted. Additionally, adjacent wiring exhibited heat damage.
Manufacturer Service Bulletins
The manufacturer had previously released two service bulletins addressing PBSI switch malfunctions linked to water ingress into the cockpit near the switches. At the time of the incident, the operator had not implemented these voluntary service bulletins.