Tailboom Locknut Could Work Loose, Causing Loss Of Control

The FAA has issued an emergency AD 2011-01-52 for Schweizer Model 269A, A 1, B, C, C-1, and Th-55 series helicopters.

File Photo

The emergency AD is prompted by a locknut working loose on the tailboom aft cluster fitting strut. Further investigation revealed that the locknut installed on the expandable bolt did not have the proper threads. This condition, if not corrected, could result in the strut and driveshaft separating from the helicopter and subsequent loss of control of the helicopter.

After evaluating all the relevant information, the FAA determined the unsafe condition is likely to exist or develop in other helicopters of these same type designs.

The AD requires, before further flight, unless accomplished previously, removing the locknut, part number MS21043-3. Reinstalling the locknut while determining the locknut drag torque is then required. If the drag torque is a minimum of 2 in-lbs, retorquing the locknut to 23 in-lbs is required. If the drag torque is not at least 2 in-lbs, replacing the locknut with an airworthy locknut is required.

Special flight permits will not be issued for the aircraft.

FMI: http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAD.nsf/0/3B72D4B5E515A376862577FF0079E131?OpenDocument