Serious incident de Havilland Canada DHC-8-311 N430AW, Monday 24 February 1997

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Date:	Monday 24 February 1997
Time:	07:36 LT
Type:	de Havilland Canada DHC-8-311
Owner/operator:	Mesa Airlines
Registration:	N430AW
MSN:	279
Year of manufacture:	1991
Total airframe hrs:	13374 hours
Engine model:	P&W PW123
Fatalities:	Fatalities: 0 / Occupants: 45
Other fatalities:	0
Aircraft damage:	None
Category:	Serious incident
Location:	Rapid City, SD - United States of America
Phase:	En route
Nature:	Unknown
Departure airport:	(KRAP)
Destination airport:	Denver, CO (KDEN)
Investigating agency:	NTSB
Confidence Rating:	Accident investigation report completed and information captured

Narrative:
The captain said that he engaged the airplane's autopilot while passing through 10,000 feet mean sea level (msl). About 10 minutes later, the crew noticed illumination of a 'PITCH MISTRIM, TRIM NOSE DOWN' annunciator light. The captain attempted to trim the airplane using the manual elevator trim, but it would allow only limited movement. The crew declared an emergency, returned to Rapid City, and landed the airplane without further incident. A postincident inspection of the aft fuselage compartment revealed that one of the two master links (which held the chain and cable assembly to the electric elevator trim system) had come apart. The chain had subsequently entangled itself in the elevator trim cables. Further examination revealed that the 'C' clip (which snaps to the two posts of the master link base plate and held the master link cover plate in place) was missing.

Probable Cause: a missing 'C' clip, which resulted in the master link coming apart, allowing the electric elevator trim chain and cable to become entangled in the elevator trim cables.

Accident investigation: