Service Difficulty Advisory

AV 2006-04
30 May 2006

Dehavilland Twin Otter DHC 6-300
Nose Wheel Steering Collar Fracture

In our Feedback publication Issue 4/2005, Service Difficulty Report (SDR) 20050408003 was included to inform you of a broken nose wheel steering collar on a DHC 6 300 aircraft. The nose wheel steering collars P/N 71-161-11 found fractured were the original aluminium collars. Bombardier does provide Service Bulletin 6/533, offering a stronger stainless steel replacement collar.

Schematic of the nose wheel steering collar on a De havilland DHC-6-300.

There is concern that the collar fractured because of incorrect handling or towing practices. Another contributing factor may have been not disconnecting the torque links before towing. After review of the towing procedures, the Maintenance Manual (MM) Instructions could be misleading and unclear.  Careful review and practice of these instructions should be considered prior to towing these aircraft.

Those facilities that overhaul the steering actuator, safety lock wire the housing end of the assembly. The rod end of the unit is usually left unlock wired and adjusted in accordance with the the MM. This may imply that only the rod end is adjustable, but actually, the lock wired housing end of the steering actuator is also adjustable during installation. Maintenance personnel may be following the MM and adjusting only the rod end side of the actuator. Following the MM procedures from start to finish may indicate a necessity to adjust, not only the rod end, but the housing end of the steering actuator. When the MM is followed from start to finish, the travel limits are adjusted so that the actuator will not contact the cylinder at either end of its travel.

Display of a fractured nose wheel steering colar on a De havilland DHC-6-300

Any further defects or occurrences should be reported to Transport Canada, Continuing Airworthiness, Ottawa, via the Service Difficulty Reporting program.

For further information, contact a Transport Canada Centre, or call Marcel Gauthier, Continuing Airworthiness, Ottawa. Telephone 613 952-4364, or facsimile 613 996-9178, or e-mail gauthmr@tc.gc.ca.

For Director, Aircraft Certification

B. Goyaniuk
Chief, Continuing Airworthiness

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