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

[Federal Register Volume 62, Number 138 (Friday, July 18, 1997)]
[Rules and Regulations]
[Pages 38447-38448]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-18932]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 97-SW-02-AD; Amendment 39-10081; AD 97-15-08]
RIN 2120-AA64


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

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule; request for comments.

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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: 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

[[Page 38448]]

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 U.S.C. 106(g), 40113, 44701.


Sec. 39.13  [Amended]

    2. Section 39.13 is amended by adding a new airworthiness directive 
to read as follows:

AD 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 a 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.

    Issued in Fort Worth, Texas, on July 10, 1997.
Eric Bries,
Acting Manager, Rotorcraft Directorate, Aircraft Certification Service.
[FR Doc. 97-18932 Filed 7-17-97; 8:45 am]
BILLING CODE 4910-13-U

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