AL 2003-03
21 March 2003
Elevator Trim Tab Control Rod Failure
A Canadian operator of a Beech King Air C90A recently experienced an in-flight emergency. The aircraft was in level flight with the autopilot engaged when the crew heard a loud "bang". The aircraft pitched up and entered a steep climb accompanied with a severe tail vibration. With the landing gear down, full nose down elevator trim, and forward force on the control column, the aircraft was controllable and landed without further incident.
The Service Difficulty Report submitted by the operator indicated failure of the L/H elevator trim tab rod assembly part number (P/N) 50-524474-13. (See photo 1)
Initial findings indicate that the elevator trim tab horn inner bushing (P/N 90-524024-1) located in the outer press fit bushing (P/N 90-610010-5) may have seized. (See photo 2) A seized inner bushing prevents the rotation necessary for the full actuation of the elevator trim tab control rod. The trim tab control rod would then be subjected to bending loads and a fracture could result.
Transport Canada strongly recommends maintainers and/or operators of Raytheon/Beech 90 series aircraft to disassemble and thoroughly inspect the elevator trim tab hardware installation. Bolt P/N AN174-7 located on the trim tab horn should be removed to ensure that the inner bushing rotates freely.
Seizure or excessive stiffness of the inner bushing cannot be determined unless disassembly is performed.
Any wear detected on the inside portion of the rod end clevis, may indicate binding of the inner bushing and necessitate replacement
An investigation by the Transportation Safety Board (TSB) and manufacturer is currently in progress.
Photo 1
Fractured Elevator Trim Control Rod P/N 50-524474-13
Inner Bushing P/N 90-524024-1
Outer Bushing P/N 90-610010-5
Further defects or occurrences should be reported to Transport Canada, Continuing Airworthiness, Ottawa via the Service Difficult Reporting program.
For further information, contact a Transport Canada Centre, or Mr. Jean Grenier, Continuing Airworthiness, Ottawa, telephone (613) 952-4343, facsimile (613) 996-9178 or e-mail grenije@tc.gc.ca.
For Director, National Aircraft Certification
Chief, Continuing Airworthiness