AD 99-04-12

This amendment adopts a new airworthiness directive (AD), applicable to McDonnell Douglas Helicopter Systems (MDHS) Model 369D, 369E, 369FF, 369H, MD500N, and MD600N helicopters, that requires a one-time visual inspection of certain input shaft coupling assemblies for pitting. This amendment is prompted by three operators' reports of discovering pitting on the internal spline teeth. The actions specified by this AD are intended to prevent failure of the spline teeth in the input shaft coupling assembly, loss of drive to the main rotor system, and subsequent loss of control of the helicopter.

Final rule

99-04-12 MCDONNELL DOUGLAS HELICOPTER SYSTEMS: Amendment 39-11036. Docket No. 97-SW-61-AD.

Applicability: Model 369D, 369E, 369FF, 369H, MD500N, and MD600N helicopters, with input shaft coupling assemblies, part number (P/N) 369F5133-1, serial number (S/N) 030829-0126 through 030829-0207, installed on main transmission, P/N 369F5100-503, and on overrunning clutch, P/N 369F5450, 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 (c) 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 within 100 hours time-in-service after the effective date of this AD, unless accomplished previously.

To prevent failure of the spline teeth in each input shaft coupling assembly (coupling assembly), loss of drive to the main rotor system, and subsequent loss of control of the helicopter, accomplish the following:

(a) Visually inspect the coupling assemblies, P/N 369F5133-1, installed on main transmission, P/N 369F5100-503, and on overrunning clutch, P/N 369F5450, for pitting under the solid film lubricant in the spline area of the coupling.

(b) If there is pitting in the splines, replace the coupling assembly with an airworthy coupling assembly, P/N 369F5133-1, that has been inspected as required by paragraph (a) of this AD.

NOTE 2: Boeing Service Bulletin SB369H-240, SB369E-085, SB500N-013, SB369D-192, SB369F-072, SB600N-003, dated September 26, 1997, pertains to this AD.

(c) 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, 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 3: 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.

(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.

(e) This amendment becomes effective on March 23, 1999.

A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) to include an airworthiness directive (AD) that is applicable to MDHS Model 369D, 369E, 369FF, 369H, MD500N, and MD600N helicopters was published in the Federal Register on May 15, 1998 (63 FR 27011). That action proposed to require a one-time visual inspection of certain input shaft coupling assemblies for pitting.

Interested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received.

One commenter states that the addition of a calendar period to supplement the time-in-service compliance time is necessary to account for the effects of corrosion which caused the internal spline pitting. The FAA does not concur for the following reasons:

The original corrosion occurred during the manufacturing process due to exposure of unprotected machined parts and porosity in the material. The corrosion was subsequently removed in normal processing and parts coated with dry lube. The corrosion is not a result of time-in-service.

After examining parts returned from the field, there is no evidence suggesting that the original corrosion damage increases with time.

The same commenter also states that there are no guidelines or references to Boeing instructions, service bulletins, or manuals given to strip the input shaft coupling assembly and perform the visual inspection. The FAA does not concur; Note 2 states that Boeing Service Bulletin SB369H-240, SB369E-085, SB500N-013, SB369D-192, SB369F-072, SB600N-003, dated September 26, 1997, pertains to the subject of the AD. No additional guidelines for stripping shaft coupling assembly and performing the visual inspection are deemed necessary because the corrosion on the input shaft coupling assemblies is obvious and easily discernible with the naked eye without stripping the shaft coupling assembly.

After careful review of the available data, including the comments noted above, the FAA has determined that air safety and the public interest require the adoption of the rule as proposed.

The FAA estimates that 82 helicopters of U.S. registry will be affected by this AD, that it will take approximately 3 work hours per helicopter to accomplish the required actions, and that the average labor rate is $60 per work hour. Required parts will cost approximately $638 per coupling assembly. Based on these figures, the total cost impact of the AD on U.S. operators is estimated to be $67,076 if the coupling assembly is replaced in all 82 helicopters.

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 FAA, Office of the Regional Counsel, Southwest Region, Attention: Rules Docket No. 97-SW-61-AD, 2601 Meacham Blvd., Room 663, Fort Worth, Texas 76137.

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 theAdministrator, 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.

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