AD 95-03-11

This amendment adopts a new airworthiness directive (AD) that is applicable to McDonnell Douglas Helicopter Systems and Hughes Helicopters, Inc. Model 369, OH-6A, and YOH-6A series helicopters. This action requires initial and repetitive inspections of the tail rotor blade abrasion strip (abrasion strip), installation of stainless steel abrasion tape over the inboard end of the abrasion strip, and as a terminating action, installation of a tail rotor blade with a new-design abrasion strip. This amendment is prompted by several incidents of riveted abrasion strips debonding and separating during flight, resulting in severe out-of-balance conditions and subsequent separation of the tail rotor gearbox from the helicopter. The actions specified in this AD are intended to prevent loss of the abrasion strip, separation of a tail rotor blade, separation of the tail rotor gearbox, and subsequent loss of control of the helicopter.

Final rule; request for comments

95-03-11 McDONNELL DOUGLAS HELICOPTER SYSTEMS AND HUGHES HELICOPTERS, INC.: Amendment 39-9147. Docket No. 94-SW-21-AD.

Applicability: Model 369, OH-6A, and YOH-6A series helicopters, with tail rotor blade assemblies, part number (P/N) 369A1613-7, 369A1613-503, 369A1613-505, 369A1613-509, 369D21606, 369D21606-509, 369D21613-11, 369D21613-31, 369D21613-41, 369D21613-51, 369D21613-71, 369D21615, 369D21615-21, 369D21615-41, or 421-088, installed, certificated in any category.

Compliance: Required as indicated, unless accomplished previously.

To prevent loss of the abrasion strip, separation of a tail rotor blade, separation of the tail rotor gearbox, and subsequent loss of control of the helicopter, accomplish the following:

(a) Within 25 hours time-in-service (TIS) or 90 calendar days, whichever occurs first, and thereafter, at intervals not to exceed 100 hours TIS, inspect the tail rotor blade abrasion strip for debonding from the tail rotor blade. Prior to conducting the repetitive inspections, remove any abrasion tape from the tail rotor blade.

(1) If the inspection reveals debonding, replace the tail rotor blade with an airworthy blade that has been modified by an installation of rivets, and install 304 stainless steel abrasion tape (.0027-inch thick) over the inboard end of the abrasion strip in accordance with steps B through H of Part I of the Accomplishment Instructions of McDonnell Douglas Helicopter Systems Service Information Notice (SIN) HN-238, DN-187, EN-80, FN-66, dated October 26, 1994.

(2) If the inspection reveals no debonding, install 304 stainless steel abrasion tape (.0027 inch thick) over the inboard end of the abrasion strip in accordance with steps B through H of Part I of the Accomplishment Instructions of McDonnell Douglas Helicopter Systems SIN HN-238, DN-187, EN-80, FN-66, dated October 26, 1994.

(b) Within 1,000 hours TIS after the effective date of this AD, replace the affected tail rotor bladesin shipsets with tail rotor blades that contain the new-design abrasion strips in accordance with Part II of the Accomplishment Instructions of SIN HN-238, DN-187, EN-80, FN-66, dated October 26, 1994. Once the new-design abrasion strips are installed on the tail rotor blades, the tail rotor assembly P/N changes as follows:

Old Tail Rotor Assembly Number
New Tail Rotor Assembly Number
369A1613-7
369A1613-11
369A1613-503
369A1613-507
369A1613-505
369A1613-507
369A1613-509
369A1613-507
369D21606
369D21606-511
369D21606-509
369D21606-511
369D21613-11
369D21613-11N
369D21613-31
369D21613-31N
369D21613-41
369D21613-61
369D21613-51
369D21613-61
369D21613-71
369D21613-61
369D21615
369D21615-N
369D21615-21
369D21615-31
369D21615-41
369D21615-31
421-088
421-088-11

(c) Installation of tail rotor blades with new-design abrasion strips installed in accordance with Part II of the Accomplishment Instructions of SIN HN-238, DN-187, EN-80, FN-66, dated October 26, 1994, constitutes a terminating action for the requirements of this AD.

(d) 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, Los Angeles Aircraft Certification Office, FAA. Operators shall submit their requests through an FAA Principal Maintenance Inspector, who may concur or comment and then send it to the Manager, Los Angeles Aircraft Certification Office.

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

(e) 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, provided there is no evidence of debonding of the abrasion strip atany point along the entire abrasion strip bond line of the tail rotor blades.

(f) The modification and replacement shall be done in accordance with McDonnell Douglas Helicopter Systems Service Information Notice HN-238, DN-187, EN-80, FN-66, dated October 26, 1994. 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 McDonnell Douglas Helicopter Systems, Technical Publications, Bldg. 530/B111, 5000 E. McDowell Road, Mesa, Arizona 85205-9797. 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.

(g) This amendment becomes effective on March 1, 1995.

On August 30, 1994, the FAA issued AD 94-18-08, Amendment 39-9021 (59 FR 46163, September 7, 1994) to require installation of abrasion strip rivets (rivets) within 25 hours time-in-service or 7 calendar days, whichever occurs first, on certain tail rotor blades. Also required are owner/operator checks of the abrasion strips for evidence of debonding along the abrasion strip bond line before the first flight of each day; a dye-penetrant and tap-test inspection to ensure the abrasion strip is secure if the owner/operator checks reveal evidence of debonding; and, if debonding is confirmed, replacement of the tail rotor blade with an airworthy blade that has been modified with the installation of rivets. Since the issuance of that AD, there have been several incidents of riveted tail rotor blade abrasion strips debonding and separating during flight, resulting in severe out-of-balance conditions, and subsequent separation of the tail rotor gearbox from the helicopter. Based on these incidents, the FAA has determined that riveting the abrasion strips alone does not create a fail-safe design. An analysis has shown that the debonding starts at the inboard end of the abrasion strip. This condition, if not corrected, could result in loss of the abrasion strip, separation of a tail rotor blade, separation of the tail rotor gearbox, and subsequent loss of control of the helicopter. Therefore, installation of stainless steel abrasion tape over the inboard end of the abrasion strips within 25 hours time-in-service (TIS) or 90 calendar days, whichever occurs first, and thereafter, at intervals not to exceed 100 hours TIS, is necessary to prevent debonding of the abrasion strip from the tail rotor and to ensure the integrity of the helicopter. However, owners and operators must install abrasion strip rivets as required by AD 94-18-08 prior to installing the stainless steel abrasion tape. Additionally, within 1,000 hours TIS, installation ofa tail rotor blade with a new-design abrasion strip is required.

The FAA has reviewed McDonnell Douglas Helicopter Systems Service Information Notice HN-238, DN-187, EN-80, FN-66, dated October 26, 1994, which describes procedures for inspection of the abrasion strips for separation or voids and replacement if separation or voids are evident; installation of 304 stainless steel abrasion tape (.0027-inch thick) over the inboard end of the abrasion strips; and replacement of existing tail rotor blades with tail rotor blades equipped with new-design abrasion strips.

Since an unsafe condition has been identified that is likely to exist or develop on other McDonnell Douglas Helicopter Systems and Hughes Helicopters, Inc. Model 369, OH-6A, and YOH-6A series helicopters of the same type design, this AD is being issued to prevent loss of the abrasion strip, separation of a tail rotor blade, separation of the tail rotor gearbox, and subsequent loss of control of the helicopter. ThisAD requires initial and repetitive inspections of the abrasion strip, installation of stainless steel abrasion tape over the inboard end of the abrasion strip, and as a terminating action, installation of a tail rotor blade with a new-design abrasion strip. Due to the criticality of the abrasion strip and maintaining a balanced tail rotor system, and the short compliance time for installation of the stainless steel abrasion tape, this rule must be issued immediately to correct an unsafe condition. The actions are required to be accomplished in accordance with the service bulletin described previously.

Since a situation exists that requires the immediate adoption of this regulation, it is found that notice and opportunity for prior public comment hereon are impracticable, and that good cause exists for making this amendment effective in less than 30 days.

Comments Invited
Although this action is in the form of a final rule that involves requirements affecting flight safety and, thus, was not preceded by notice and an opportunity for public comment, comments are invited on this rule. Interested persons are invited to comment on this rule by submitting such written data, views, or arguments as they may desire. Communications should identify the Rules Docket number and be submitted in triplicate to the address specified under the caption "ADDRESSES." All communications received on or before the closing date for comments will be considered, and this rule may be amended in light of the comments received. Factual information that supports the commenter's ideas and suggestions is extremely helpful in evaluating the effectiveness of the AD action and determining whether additional rulemaking action would be needed.

Comments are specifically invited on the overall regulatory, economic, environmental, and energy aspects of the rule that might suggest a need to modify the rule. All comments submitted will be available, both before and after the closingdate for comments, in the Rules Docket for examination by interested persons. A report that summarizes each FAA-public contact concerned with the substance of this AD will be filed in the Rules Docket.

Commenters wishing the FAA to acknowledge receipt of their comments submitted in response to this rule must submit a self-addressed, stamped postcard on which the following statement is made: "Comments to Docket No. 94-SW-21-AD." The postcard will be date stamped and returned to the commenter.

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.

The FAA has determined that this regulation is an emergency regulation that must be issued immediately to correct an unsafe condition in aircraft, and that it is not a "significant regulatory action" under Executive Order 12866. It has been determined further that this action involves an emergency regulation under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979). If it is determined that this emergency regulation otherwise would be significant under DOT Regulatory Policies and Procedures, a final regulatory evaluation will be prepared and placed in the Rules Docket. A copy of it, if filed, 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 adding a new airworthiness directive to read as follows: