AD 94-14-20

This amendment supersedes an existing airworthiness directive (AD), applicable to Sikorsky Aircraft Model S-76A series helicopters, that currently requires an initial and repetitive inspections of the tail rotor (T/R) blade spar elliptical centering plug (centering plug) for disbonding and adds a retaining pad between the T/R gearbox output shaft and the inboard T/R spar. This amendment requires the same design changes and procedures as the previous AD, except that it would eliminate the 500 hours' time-in-service repetitive inspections for centering plug disbonding. This amendment is prompted by an improved bonding and repair procedure and the lack of reports concerning the movement or disbonding of the centering plug. The actions specified by this AD are intended to prevent the centering plug from disbonding and moving out of position, which could result in loss of tail rotor control, and subsequent loss of control of the helicopter.

Final rule

94-14-20 SIKORSKY AIRCRAFT: Amendment 39-8969. Docket Number 93-SW-13-AD. Supersedes AD 84-06-02, Amendment 39-4829.

Applicability: Model S-76A Series helicopters, certificated in any category.

Compliance: Required within the next 25 hours' time-in-service after the effective date of this AD, unless accomplished previously.

To prevent the tail rotor blade (T/R) spar elliptical centering plug (centering plug) from disbonding and moving out of position, which could result in loss of tail rotor control and loss of control of the helicopter, accomplish the following for blades, part numbers (P/N) 76101-05001 and 76101-05101 series, with more than 130 hours' time-in-service:

(a) Remove the blades in accordance with the maintenance manual and inspect the centering plug for disbonding of the polyurethane filler that fills the space between the aluminum centering plug and the graphite T/R spar in accordance with Sikorsky Aircraft Alert Service Bulletin 76-65-35A, Revision A, dated February 29, 1984 (ASB).

(1) If the inspection of the centering plug shows no evidence of disbonding greater than one-half inch in length, install a retaining pad in accordance with paragraph 2.C. of the Accomplishment Instructions of the ASB.

(2) For disbonds greater than one-half inch, but less than 2 inches in length, repair the blade in accordance with paragraph 2.B.(1) of the Accomplishment Instructions of the ASB.

(3) For disbonds equal to or greater than 2 inches in length, but not complete disbonds, or for disbonded centering plugs with the polyurethane filler excessively cracked or deteriorated to the extent of breaking away from the T/R spar or the centering plug, remove the blade from service and replace with an airworthy blade.

(4) For T/R spars with complete T/R spar to centering plug disbond in which the polyurethane filler is intact and remains fully bonded to the centering plug, repair in accordance with paragraph 2.B.(2) of the Accomplishment Instructions of the ASB.

(5) For T/R spars with complete polyurethane filler to centering plug disbond in which the polyurethane filler is intact and remains fully bonded to the T/R spar, repair in accordance with paragraph 2.B.(3) of the Accomplishment Instructions of the ASB.

(b) Install retaining pad, P/N 76102-05004-111, in accordance with paragraph 2.C. of the Accomplishment Instructions of the ASB.

(c) An alternative method of compliance or adjustment of the compliance time that provides an acceptable level of safety may be used when approved by the Manager, Boston Aircraft Certification Office. Operators shall submit their requests through an FAA Principal Maintenance Inspector, who may concur or comment and then send it to the Manager, Boston Aircraft Certification Office.

NOTE: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Boston Aircraft Certification Office.

(d) Special flight permits may be issued in accordance with sections 21.197 and 21.199 of the Federal Aviation Regulations (14 CFR 21.197 and 21.199) to operate the helicopter to a location where the requirements of this AD can be accomplished if a retaining pad has been installed.

(e) The inspections and repair shall be done in accordance with Sikorsky Aircraft Alert Service Bulletin 76-65-35A, Revision A, dated February 29, 1984. This 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 Sikorsky Aircraft, Commercial Customer Support, 6900 Main Street, Stratford, Connecticut 06601-1381. Copies may be inspected at the FAA, Office of the Assistant Chief Counsel, 2601 Meacham Blvd., Room 663, Fort Worth, Texas; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC.

(f) This amendment becomes effective on September 15, 1994.

A proposal to amend part 39 of the Federal Aviation Regulations by superseding AD 84-06-02, Amendment 39-4829 (49 FR 10922, March 23, 1984) which is applicable to Sikorsky Aircraft Model S-76A series helicopters, was published in the Federal Register on August 4, 1993 (58 FR 41442). That action proposed to require the same design changes and procedures as the previous AD, except that it would eliminate the 500 hours' time-in- service repetitive inspections for centering plug disbonding. This amendment is prompted by an improved bonding and repair procedure and the lack of reports concerning the movement or disbonding of the centering plug.

Interested persons have been afforded an opportunity to participate in the making of this amendment. No comments were received on the proposal or the FAA's determination of the cost to the public. However, for consistency of word usage throughout the AD and to make the language more consistent with the SikorskyAircraft Alert Service Bulletin 76-65-35A, Revision A, dated February 29, 1984, the word "pressure" that describes the part has been changed to "retaining" and all forms of the word "debond" have been changed to "disbond." Other minor editorial changes were made, also. Therefore, the FAA has determined that air safety and the public interest require the adoption of the rule with the changes previously described. The FAA has determined that these changes will neither increase the economic burden on any operator nor increase the scope of the AD.

There are approximately 190 Sikorsky Aircraft Model S-76A series helicopters of the affected design in the worldwide fleet. The FAA estimates that 150 helicopters of U.S. registry will be affected by this AD, that it will save approximately 4 work hours per helicopter by discontinuing the current 500 hours' time-in-service repetitive inspections, and that the average labor rate is $55 per work hour. Based on these figures, the annual cost savings of the proposed elimination of these AD inspections on U.S. operators is estimated to be $33,000 annually.

The regulations adopted herein will not have substantial direct effects on the States, on the relationship between the national government and the States, or on the distribution of power and responsibilities among the various levels of government. Therefore, in accordance with Executive Order 12612, it is determined that this final rule does not have sufficient federalism implications to warrant the preparation of a Federalism Assessment.

For the reasons discussed above, I certify that this action (1) is not a "significant regulatory action" under Executive Order 12866; (2) is not a "significant rule" under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and (3) will not have a significant economic impact, positive or negative, on a substantial number of small entities under the criteria of the Regulatory Flexibility Act. A final evaluation has been prepared for this action and it is contained in the Rules Docket. A copy of it may be obtained from the Rules Docket at the location provided under the caption "ADDRESSES."

List of Subjects in 14 CFR Part 39
Air transportation, Aircraft, Aviation safety, Incorporation by reference, Safety.

Adoption of the Amendment
Accordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration amends part 39 of the Federal Aviation Regulations (14 CFR part 39) as follows:

PART 39 - AIRWORTHINESS DIRECTIVES
1. The authority citation for part 39 continues to read as follows:
Authority: 49 U.S.C. App. 1354(a), 1421 and 1423; 49 U.S.C. 106(g); and 14 CFR 11.89.

39.13 - [AMENDED]
2. Section 39.13 is amended by removing Amendment 39-4829, (49 FR 10922, March 23, 1984), and by adding a new airworthiness directive (AD), Amendment 39-8969, to read as follows: