NTSB Identification: CHI97IA073.
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Scheduled 14 CFR operation of MESABA AIRLINES
Incident occurred Thursday, February 20, 1997 in ROMULUS, MI
Probable Cause Approval Date: 01/30/1998
Aircraft: de Havilland DHC-8-102, registration: N828MA
Injuries: 26 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 captain said that after departure, 'the first officer needed excessive right wing down trim to maintain a wings level attitude. The left outboard roll spoiler indicated approximately one-half deployment on the PFCS (Powered Flight Controlled Surfaces).' The crew maintained control of the airplane with trim and control wheel input. The crew declared an emergency, returned to the airport, and landed the airplane without further incident. A postincident inspection revealed that the left outboard roll spoiler was 'deployed approximately half-way.' An examination and disassembly of the roll spoiler servoactuator revealed that a plug (PN A50993-1), which had been fusion-welded into the base of the piston (PN A50992-1), had separated and lodged itself between the base of the piston and the shims, restricting the piston's movement. Dowty Aerospace (the manufacturer) had recorded seven previous failures of fusion welds in pistons on DHC-8 roll spoiler servoactuators before this incident.

The National Transportation Safety Board determines the probable cause(s) of this incident to be:

a fractured fusion weld in the piston of the roll spoiler servoactuator, which allowed the plug at the base of the piston to separate and jam the piston. A factor relating to the incident was: the inadequate design of the airplane's roll spoiler servoactuator piston.

Full narrative available

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