Airworthiness Directive · Amendment 39-16408 · Sikorsky Aircraft Corporation Model S-76A, S-76B, and S-76C Helicopters
Sikorsky Aircraft Corporation Model S-76A, S-76B, and S-76C Helicopters
Model S-76A, S-76B, and S-76C helicopters, with serial numbers 76005 through 760578, inclusive, and serial number 762976, with any of the following part-numbered vertical stabilizer aft spar assemblies having 1,000 or more hours time-in-service (TIS) installed, certificated in any category.
| Helicopter model | Vertical stabilizer aft spar assembly part number |
|---|---|
| S-76A | 76201-05002-114 |
| 76201-05002-115 | |
| S-76B and S-76C | 76201-05002-047 |
| 76201-05002-048 | |
| 76201-25002-041 | |
| 76201-25002-044 | |
| 76201-25002-045 | |
| 76201-25002-046 |
We are adopting a new airworthiness directive (AD) for Sikorsky Aircraft Corporation (Sikorsky) Model S-76A, S-76B, and S-76C helicopters. This AD requires an initial and recurring inspections of the tail rotor vertical stabilizer aft spar assembly (aft spar assembly) for a crack, loose or working fasteners, and corrosion, and, if any are found, further inspections of the vertical stabilizer forward spar assembly (forward spar assembly). Repairing or replacing any unairworthy part before further flight is also required. This AD also requires a recurring track-and-balance of the tail rotor. Finally, this AD requires installing a vertical stabilizer modification kit, which is terminating action for the requirements of the AD. This AD is prompted by 26 reports of fatigue cracks in the aft spar assembly web and outer caps. The actions specified by this AD are intended to detect and correct an unbalanced or out-of-track tail rotor, which could lead to increased vibrations, a fatigue crack, loss of a portion of the vertical stabilizer and subsequent loss of control of the helicopter.
To detect and correct an unbalanced or out-of-track tail rotor, which could lead to increased vibrations, a fatigue crack, loss of a portion of the vertical stabilizer, and subsequent loss of control of the helicopter, accomplish the following:
(a) Within 30 days, unless accomplished previously, and thereafter at intervals not to exceed 50 hours TIS, inspect the vertical stabilizer aft spar assembly (aft spar assembly) for a crack, a loose or working fastener, or corrosion in accordance with the Accomplishment Instructions, paragraph 3.A., in Sikorsky Alert Service Bulletin (ASB) No. 76-55-20A, Revision A, dated November 11, 2003 (No. 76-55-20A). For purposes of this AD, ASB No. 76-55-20A is applicable to Model S-76B helicopters as well as Model S-76A and S-76C helicopters.
(1) If a crack, a loose or working fastener, or corrosion is found in the aft spar assembly, before further flight:
(i) Repair or replace any unairworthy parts and
(ii) Inspect the vertical stabilizer forward spar assembly (forward spar assembly) for a crack, a loose or working fastener, or corrosion in accordance with the Accomplishment Instructions, paragraph 3.B., in ASB No. 76-55-20A. Contacting the manufacturer is not required by this AD.
(2) If a crack, a loose or working fastener, or corrosion is found in the forward spar assembly, repair in accordance with the applicable maintenance manual or replace with airworthy parts before further flight.
(b) Within 30 days, unless accomplished previously, and thereafter at intervals not to exceed 200 hours TIS, track-and-balance the tail rotor in accordance with the Accomplishment Instructions, paragraph 3.A., in ASB No. 76-65-58A, Revision A, dated November 11, 2003.
Note 1: Although the ASB specifies only an initial inspection of the aft spar assembly and a track and balance of the tail rotor, this AD requires inspecting the aft spar assembly and track-and-balancing the tail rotor repetitively.
Note 2: The track-and-balancing of the tail rotor that is required by paragraph (b) of this AD involves both a pilot and mechanic. The pilot's function is to operate the helicopter to a “light on wheels” state—almost to the point of takeoff. The mechanic is needed to accomplish the vibration measurements.
(c) On or before December 31, 2010, install a vertical stabilizer modification kit, part number 76070-20562-011, 76070-20563-011, or 76070-20564-011. Installing the vertical stabilizer modification kit is terminating action for the requirements of this AD.
(d) To request a different method of compliance or a different compliance time for this AD, follow the procedures in 14 CFR 39.19. Contact the Manager, Boston Aircraft Certification Office, Engine and Propeller Directorate, ATTN: Nicholas Faust, Aviation Safety Engineer, FAA, 12 New England Executive Park, Burlington, MA 01803, telephone (781) 238-7763, fax (781) 238-7170, for information about previously approved alternative methods of compliance.
(e) The Joint Aircraft System/Component (JASC) Code 5530 is: Vertical Stabilizer.
The aircraft, engines and makers this AD names, by the model designations in its text. A model listed here may still be outside the AD's serial ranges.
