AD 86-20-07

86-20-07 MCDONNELL DOUGLAS HELICOPTER COMPANY (Hughes Helicopters, Inc.): Amendment 39-5422. Applies to Model 369, 369A, 369D, 369E, 369H, 369HE, 369HM, and 369HS helicopters, including military Models YOH-6A and OH-6A, certificated in any category, equipped with tail rotor drive shaft flexible couplings, Part Number (P/N) 369A5501 or 369H92564.

Compliance required as indicated unless already accomplished.

To prevent failure of the tail rotor (T/R) drive shaft system and subsequent loss of T/R control, accomplish the following:

(a) Within 100 hours' time in service after the effective date of this AD, install aft coupling failsafe device (P/N's 369D25530 bolt and 369D25531 socket) in accordance with Part I of the applicable Service Information Notices (SIN) DN-143, HN-2O6, or EN-31, each dated August 26, 1986. Installation of the failsafe device on military Models YOH-6A or OH-6A helicopters in civil use shall be accomplished in accordance with Part I of SIN HN-206.

NOTE: The failsafe device required by paragraph (a) will be installed before delivery on all applicable Model 369E helicopters, Serial Number 0135E, and subsequent.

(b) Within 100 hours' time in service after the effective date of this AD, install forward coupling failsafe device (P/N's 369D25530 bolt and 369D25531 socket) in accordance with Part I of SIN DN-95, dated August 7, 1981, or Part III, HN-173, dated November 2, 1981, as applicable. Installation of the coupling failsafe device on military Models YOH-6A or OH-6A helicopters shall be accomplished in accordance with Part III of SIR HN-173.

(c) For all helicopters with tail rotor driveshaft flexible coupling failsafe devices installed, the T/R drive shaft forward and aft flexible couplings shall be checked as follows:

(1) (At Each Preflight Check: Check for T/R backlash or looseness by rocking the T/R back and forth in its plane of rotation. The blade should not move in excess of 0.75 inch (1.93cm) atthe blade tip without rotation of the main rotor blades.

(2) At Each Aircraft/Engine Shutdown: If thumping or rapping is heard from the T/R drive train during final revolutions of the T/R, check the T/R to assure that the T/R blade does not move in excess of 0.75 inch (1.93cm) at the blade tip without rotation of main rotor blades.

(d) The checks required by this AD may be performed by the pilot and must be recorded in accordance with FAR Section 91.173.

(e) If during the checks required by paragraph (c), the tail rotor blade tip movement exceeds the specified limits, prior to further flight, inspect and replace, as necessary, either or both fore and aft tail rotor drive shaft couplings.

(f) Rotorcraft may be ferried in accordance with the provisions of FAR Sections 21.197 and 21.199 to a base where the modifications and inspections of paragraphs (a) and (b) of this AD can be accomplished.

(g) An alternate method of compliance which provides an equivalent level of safety may be approved by the Manager, Western Aircraft Certification Office, P.O. Box 92007, Worldway Postal Center, Los Angeles, California 90009-2007.

The procedure shall be done in accordance with applicable parts of MDHC SIN's DN- 143, HN-206, EN-31, all dated August 26, 1986; MDHC SIN DN-95, dated August 7, 1981; MDHC SIN HN-173, dated November 2, 1981. The incorporation by reference was approved by the Director of the FEDERAL REGISTER in accordance with 5 U.S.C. 552(a) and 1 CFR Part 51. Copies may be obtained from McDonnell Douglas Helicopter Company, Centinela Avenue and Teal Street, Culver City, California 90230. These documents may be examined at the Office of the Regional Counsel, Federal Aviation Administration, Southwest Region, Room 158, Building 3B, 4400 Blue Mound Road, Fort Worth, Texas 76101, the Western Aircraft Certification Office, 15000 Aviation Boulevard, Hawthorne, California, or the Office of the FEDERAL REGISTER, 1100 L Street, NW., Room 8401,Washington, D.C.

This amendment supersedes Amendment 39-4186 (46 FR 40868), AD 81-17-02, as amended by Amendment 39-4221 (46 FR 46566), AD 81-17-02R1. This amendment becomes effective October 24, 1986.