AD 97-15-08

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AD Number:
97-15-08
Document Type:
AD Final Rules
Docket Number:
97-SW-02-AD
Subject Heading:
Airworthiness Directives; McDonnell Douglas Helicopter Systems Model 369D, E, F, FF, 500N, AH-6, and...Show more
Subject:
Transmission Output Drive Gear
Status:
Current
Citation:
Federal Register: July 18, 1997 (Volume 62, Number 138)
Citation Publish Date:
07/18/1997
Effective Date:
08/04/1997
Make:
MD Helicopters, Inc.
Model:
369D | 369E | 369F | 369FF | 500N
Product Type:
Aircraft
Product Subtype:
Rotorcraft
Affected AD:
Superseded AD:
Affected By:
Superseded By:
Service/Office:
Office of Primary Responsibility:
CFR Part Reference:
Part 39 [62 FR 38447 NO. 138 07/18/97]
Comments:
AIRWORTHINESS DIRECTIVES FINAL RULES: 97-15-08
CITATION:   [Federal Register: July 18, 1997 (Volume 62, Number 138)]

PAGE NUMBER:   [Page 38447]

DOCKET NUMBER:   97-SW-02-AD

AMENDMENT:   39-10081

AD NUMBER:   97-15-08

SUBJECT HEADING:   Airworthiness Directives; McDonnell Douglas Helicopter Systems Model 369D, E, F, FF, 500N, AH-6, and MH-6 Helicopters

ACTION:   Final rule; request for comments

SUMMARY:   This amendment adopts a new airworthiness directive (AD) that is applicable to McDonnell Douglas Helicopter Systems (MDHS) Model 369D, E, F, FF, 500N, AH-6, and MH-6 helicopters. This action requires replacement of certain transmission output drive gears (gears). This amendment is prompted by several reports of spalled or fractured gear teeth, most of which occurred during high-power or external-lift operations. The actions specified in this AD are intended to prevent failure of the gear, which could result in loss of main rotor control and subsequent loss of control of the helicopter.

DATES:   Effective August 4, 1997. Comments for inclusion in the Rules Docket must be received on or before September 16, 1997.

ADDRESSES:   Submit comments in triplicate to the Federal Aviation Administration (FAA), Office of the Assistant Chief Counsel, Attention: Rules Docket No. 97-SW-02-AD, 2601 Meacham Blvd., Room 663, Fort Worth, Texas 76137.

FOR FURTHER INFORMATION CONTACT:   Mr. Bruce Conze, Aerospace Engineer, FAA, Los Angeles Aircraft Certification Office, Propulsion Branch, 3960 Paramount Blvd., Lakewood, California 90712, telephone (562) 627-5261, fax (562) 627-5210.

SUPPLEMENTARY INFORMATION:  

This amendment adopts a new AD that is applicable to MDHS Model 369D, E, F, FF, 500N, AH-6, and MH-6 helicopters, equipped with main rotor transmission, part number (P/N) 369D25100, that contain a gear, P/N 369D25127-11, having the following serial numbers: serial number (S/N) 005570-0646 through S/N 005570-0765, and S/N 005570-0876 through S/N 005570-0998. This action requires replacement of gears having the affected serial numbers within a specified number of hours time-in-service (TIS). There have been several occurrences of spalled or fractured gear teeth in the last seven years. Five of the occurrences involved fractured gear teeth, and two involved spalling of the gear tooth face. All seven failures occurred on helicopters having less than 1,000 hours TIS, with the lowest being 467 hours TIS. Most of the damage and subsequent failures have occurred during high-power or external-lift operations conducted on military aircraft. This amendment is prompted by several reports of spalled or fractured gear teeth, most of which occurred during high-power or external-lift operations. Until 1996, all failures had occurred only in military operations in which it was thought to be due to overtorquing during maximum effort exercises. Since there is no reporting requirement for military use, those failures were handled under military maintenance and not reported. In 1996, a similar failure occurred in New Zealand with an external load operator. This was the first commercial failure and the first reported to the FAA by MDHS. MDHS was allowed time to examine the failure and determine the cause. Once it was determined that the failure was due to a quality control problem, the affected lots were identified and MDHS issued service information. Warping of the ring gear during carburizing heat treatment and subsequent grinding through the hardened case results in a lowering of the contact stress and fatigue resistance of the gear teeth. This could result in fracture or loss of a gear tooth, which could lead to jamming or binding of the drive system. The actions specified in this AD are intended to prevent failure of the gear, which could result in loss of main rotor control and subsequent loss of control of the helicopter.

The FAA has reviewed McDonnell Douglas Helicopter Systems Service Information Notice DN- 189/EN-82/FN-69/NN-009, dated January 10, 1997, which describes procedures for determining, through an inspection of records or physical inspection, if a gear, P/N 369D25127-11, with serial number (S/N) S/N 005570-0646 through S/N 005570-0765, or S/N 005570-0876 through S/N 005570-0998 is installed.

Since an unsafe condition has been identified that is likely to exist or develop on other MDHS Model 369D, E, F, FF, 500N, AH-6, and MH-6 helicopters of the same type design, this AD is being issued to prevent failure of the gear, which could result in loss of main rotor control and subsequent loss of control of the helicopter. This AD requires an inspection to determine if an affected gear (based on the gear's serial number) is installed, and if an affected gear is installed, replacement of the gear with an airworthy gear.

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 closing date 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. 97-SW-02-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, 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 USC 106(g), 40113, 44701.

§ 39.13 - [Amended]
2. Section 39.13 is amended by adding a new airworthiness directive to read as follows:

REGULATORY TEXT:  
97-15-08 MCDONNELL DOUGLAS HELICOPTER SYSTEMS: Amendment 39-10081. Docket No. 97-SW-02-AD.

Applicability: Model 369D, E, F, FF, 500N, AH-6, and MH-6 helicopters, with main rotor transmission, part number (P/N) 369D25100, installed, certificated in any category.

NOTE 1: This AD applies to each helicopter identified in the preceding applicability provision, regardless of whether it has been modified, altered, or repaired in the area subject to the requirements of this AD. For helicopters that have been modified, altered, or repaired so that the performance of the requirements of this AD is affected, the owner/operator must use the authority provided in paragraph (d) to request approval from the FAA. This approval may address either no action, if the current configuration eliminates the unsafe condition, or different actions necessary to address the unsafe condition described in this AD. Such a request should include an assessment of the effect of the changed configuration on the unsafe condition addressed by this AD. In no case does the presence of any modification, alteration, or repair remove any helicopter from the applicability of this AD.

Compliance: Required as indicated, unless accomplished previously.

To prevent failure of the transmission output drive gear (gear), part number P/N 369D25127- 11, which could result in loss of main rotor control and subsequent loss of control of the helicopter, accomplish the following:

(a) Within the next 10 hours time-in-service (TIS) after the effective date of this AD, determine through an inspection of records, contact with the manufacturer, or using a bright light and viewing through the open liquid level plug port, if the installed gear serial number (S/N) is S/N 005570-0646 through S/N 005570-0765, or S/N 005570-0876 through S/N 005570-0998.

(b) If the gear has an affected S/N, remove the gear and replace it with an airworthy gear, that has a S/N other than the S/N's listed in paragraph (a) of this AD, as follows:

(1) For helicopters equipped with a cargo hook assembly, with a separate, permanently-maintained log of actual hours time-in-service (TIS) of external load operation, remove and replace the gear within the next 25 hours TIS for external load operations, or within the next 400 hours TIS for non-external load operation, whichever comes first.

(2) For helicopters equipped with a cargo hook assembly, with no separate, permanently- maintained log of actual external load operation, remove and replace the gear within the next 25 hours TIS after the effective date of this AD. Owners/operators may begin maintaining a separate permanent log of external load operations and comply with the requirements of paragraph (b)(1) of this AD.

(3) For helicopters without cargo hook assemblies, remove and replace the gear within the next 400 hours TIS after the effective date of this AD.

(c) Replacement of the affected gear with an airworthy gear having a S/N other than those S/N's listed in paragraph (a) of this AD is considered 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 if approved by the Manager, Los Angeles 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, Los Angeles Aircraft Certification Office.

NOTE 2: 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.

(f) This amendment becomes effective on August 4, 1997.

FOOTER: