Airworthiness Directive · Amendment 39-16723 · Rotorcraft tailboom
Schweizer Aircraft Corporation (Schweizer) Model 269A, A-1, B, C, C-1, and TH-55 Series Helicopters
Schweizer Model 269A, A-1, B, C helicopters (serial number (S/N) 1846 and larger); C-1 helicopters (S/N 0156 and larger); and TH-55 series helicopters with an Aft Cluster Fitting Modification Kit, part number (P/N) SA-269K-106, installed; certificated in any category.
We are superseding an existing emergency airworthiness directive (EAD) for the specified Schweizer model helicopters that was previously sent to all known U.S. owners and operators. That EAD currently requires removing each locknut and verifying sufficient drag torque and retorquing, or if the locknut does not have sufficient drag torque, replacing the locknut with an airworthy locknut. This AD retains the existing EAD requirements but also requires within a specified time, modifying the expandable bolts and installing a cotter pin. This AD is prompted by a locknut working loose from a bolt attaching the tailboom support strut at the aft cluster fitting because the locknut installed on the expandable bolt did not have the proper threads. We are issuing this AD to modify each expandable bolt to allow adding a cotter pin to prevent the strut and driveshaft separating from the helicopter and subsequent loss of control of the helicopter.
Required as indicated, unless already done.
(1) Before further flight, remove both the left-hand and right-hand locknuts, P/N MS21043-3. Reinstall the locknuts while determining the locknut drag torque. If the drag torque is a minimum of 2 in-lbs., retorque the locknut to 23 in-lbs. If the drag torque is not at least 2 in-lbs, replace the locknut with an airworthy locknut.
(2) Within 10 hours time-in-service, modify each expandable bolt, P/N ADB221-1A, torque locknut, P/N MS21043-3, and install cotter pin, P/N MS24665-132 or MS24665-151, in accordance with the Procedure Section, Part II, of Schweizer Service Bulletin (SB) No. B-295, dated December 21, 2010, for Model 269A, A-1, B, C, and TH-55 series helicopters or SB No. C1B-032, dated December 21, 2010, for Model 269C-1 helicopters.
(3) Before installing an expandable bolt, P/N ADB221-1A, to secure the tailboom support strut to the tailboom aft cluster fitting, modify the expandable bolt in accordance with paragraph (e)(2) of this AD.
(f) Modifying both expandable bolts by torquing the locknuts and installing the cotter pins as required by this AD is terminating action for the requirements of paragraph (e)(1) and (e)(2) of this AD.
