AL 2003-04
16 May 2003
Horizontal Stab Actuator Lubrication
Following take off of a float equipped DHC 3T Otter, the control column pitched violently fore and aft before returning to a neutral position. The aircraft then pitched down and contacted the water in a nose down, wings level attitude. The aircraft sustained substantial damage and sank. The occupants escaped without serious injury.
Investigation revealed the cable-operated jackscrew P/N C3CF290-7 jammed due to internal corrosion of the jackscrew. Once jammed, the rivet securing the fork end (See detail A) to the actuator sheared resulting in a "free floating" horizontal stabilizer. This corrosion could have been prevented with adequate lubrication as required by existing maintenance instructions.
The grease nipple on the screw jack actuator allows for lubrication of the ferrule at the rod end only and not the internal mechanism of the actuator. See detail B.
Proper lubrication and inspection of this component, part number C3CF290-7 or -9, requires removal and disassembly at each 400-hour inspection interval. Reference
Maintenance Manual PSM 1-3-2, Part 1, Lubrication diagram 1-14, part 2, paragraph 2.27.4 and the Inspection Schedule Appendix IV.
To preclude further occurrences of this nature, Transport Canada alerts operators of this aircraft model to ensure the instructions for lubrication of the horizontal stabilizer actuator jack are precisely followed.
For further information, contact a Transport Canada Center, or Mr. Paul Jones, Continuing Airworthiness Ottawa, telephone (613) 952-4431, facsimile (613) 996-9178 or e-mail jonesp@tc.gc.ca.
For further information, contact a Transport Canada Centre, or Mr. Paul Jones, Continuing Airworthiness, Ottawa, telephone (613) 952-4431, facsimile (613) 996-9178 or e-mail jonesp@tc.gc.ca.
For Director, National Aircraft Certification
Robin Lau
Acting Chief, Continuing Airworthiness