NTSB Identification: CHI94IA095.
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Scheduled 14 CFR operation of UNITED FEEDER SERVICE (D.B.A. UNITED EXPRESS )
Incident occurred Friday, February 25, 1994 in MOSINEE, WI
Probable Cause Approval Date: 01/26/1995
Aircraft: BRITISH AEROSPACE ATP, registration: N854AW
Injuries: 2 Minor,16 Uninjured.
NTSB investigators used data provided by various sources and may not have traveled in support of this investigation to prepare this aircraft incident report.
THE FLIGHT CREW SAW SMOKE IN THE COCKPIT WHILE DESCENDING FROM CRUISE AND DECLARED AN EMERGENCY. THE COPILOT DISCOVERED THE SOURCE OF THE SMOKE TO BE A RED-HOT PUSH BUTTON SELECTOR INDICATOR (PBSI) SWITCH FOR THE FLIGHT IDLE BAULK TEST. HE DISCHARGED A PORTABLE FIRE EXTINGUISHER ON THE SWITCH AND THE SMOKE STOPPED. THE SWITCH WAS SUBSEQUENTLY REMOVED BY MAINTENANCE PERSONNEL AND FOUND TO SCORCHED AND MELTED. ADJACENT WIRING WAS ALSO HEAT DAMAGED. THE MANUFACTURER HAD PREVIOUSLY ISSUED TWO SERVICE BULLETINS WHICH DEALT WITH PBSI SWITCH MALFUNCTIONS ASSOCIATED WITH WATER INGRESS TO THE COCKPIT IN THE VICINITY OF THE SWITCHES. THE OPERATOR HAD NOT COMPLIED WITH THE VOLUNTARY SERVICE BULLETINS AT THE TIME OF THE INCIDENT.
The National Transportation Safety Board determines the probable cause(s) of this incident to be: the inadequate design of the PBSI electrical switch(es), and the operator's failure to expeditiously implement corrective Service Bulletins. Full narrative available
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