AD 97-07-10

This amendment adopts a new airworthiness directive (AD) that applies to de Havilland DHC-6 series airplanes that do not have a certain wing strut modification (Modification 6/1581) incorporated. This action requires inspecting the wing struts for cracks or damage (chafing, etc.), replacing wing struts that are found damaged beyond certain limits or are found cracked, and incorporating Modification No. 6/1581 to prevent future chafing damage. This AD results from several reports of wing strut damage caused by the upper fairing rubbing against the wing strut. The actions specified by this AD are intended to prevent failure of the wing struts, which could result in loss of control of the airplane.

Final rule.

97-07-10 DEHAVILLAND: Amendment 39-9984; Docket No. 93-CE-45-AD.

Applicability: Models DHC-6-1, DHC-6-100, DHC-6-200, and DHC-6-300 airplanes (all serial numbers), certificated in any category, that do not have Modification No. 6/1581 incorporated.

NOTE 1: Modification No. 6/1581 consists of installing a preformed nylon shield around the area of each wing strut at the upper end closest to the wing.

NOTE 2: This AD applies to each airplane 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 airplanes that have been modified, altered, or repaired so that the performance of the requirements of this AD is affected, the owner/operator must request approval for an alternative method of compliance in accordance with paragraph (d) of this AD. The request should include an assessment of the effect of the modification, alteration, or repair on the unsafe condition addressed by this AD; and, if the unsafe condition has not been eliminated, the request should include specific proposed actions to address it.

Compliance: Required as indicated, unless already accomplished.

To prevent failure of the wing struts, which could result in loss of control of the airplane, accomplish the following:

(a) Within the next 100 hours time-in-service (TIS) after the effective date of this AD, inspect the wing struts, part number (P/N) C6W1005 (or FAA-approved equivalent), for cracks or damage (chafing, etc.) in accordance with the ACCOMPLISHMENT INSTRUCTIONS section of de Havilland Service Bulletin (SB) No. 6/342, dated February 23, 1976.

(1) If damage is found on a wing strut that exceeds 0.025-inch in depth, exceeds a total length of 5 inches, or where any two places of damage are separated by less than 10 inches of undamaged surface over the length of the strut, prior to further flight, replace the wing strut with an airworthyFAA-approved part in accordance with the applicable maintenance manual.

(2) If any crack is found, prior to further flight, replace the wing strut with an airworthy FAA-approved part in accordance with the applicable maintenance manual.

(3) If damage is found on a wing strut that exceeds 0.010-inch in depth, provided the damage does not exceed 0.025-inch in depth, the damage does not exceed a total length of 5 inches, and where any two places of damage are separated by a minimum of 10 inches undamaged surface over the length of the strut, within 500 hours TIS after the inspection specified in paragraph (a) of this AD, replace the wing strut with an airworthy FAA-approved part in accordance with the applicable maintenance manual.

(b) Within the next 600 hours TIS after the effective date of this AD, incorporate Modification No. 6/1581 in accordance with the ACCOMPLISHMENT INSTRUCTIONS section of de Havilland SB No. 6/342, dated February 23, 1976.

(1) IncorporatingModification No. 6/1581 eliminates the repetitive inspection requirement of this AD.

(2) Incorporating Modification No. 6/1581 may be accomplished at any time prior to 600 hours TIS after the effective date of this AD, at which time it must be incorporated.

(c) 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 airplane to a location where the requirements of this AD can be accomplished.

(d) An alternative method of compliance or adjustment of the compliance times that provides an equivalent level of safety may be approved by the Manager, New York Aircraft Certification Office (ACO), FAA, 10 Fifth Street, 3rd Floor, Valley Stream, New York 11581. The request shall be forwarded through an appropriate FAA Maintenance Inspector, who may add comments and then send it to the Manager, New York ACO.

NOTE 3: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the New York ACO.

(e) The inspections and modification required by this AD shall be done in accordance de Havilland Service Bulletin No. 6/342, dated February 23, 1976. 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 de Havilland, Inc., 123 Garratt Boulevard, Downsview, Ontario M3K 1Y5 Canada. Copies may be inspected at the FAA, Central Region, Office of the Assistant Chief Counsel, Room 1558, 601 E. 12th Street, Kansas City, Missouri, or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC.

(f) This amendment becomes effective on May 23, 1997.

Discussion

A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) to include an AD that would apply to de Havilland DHC-6 series airplanes that do not have a certain wing strut modification (Modification 6/1581) incorporated was published in the Federal Register as a notice of proposed rulemaking (NPRM) on October 3, 1996 (61 FR 51619). The NPRM proposed to require inspecting the wing struts for cracks or damage (chafing, etc.), replacing wing struts that are found damaged beyond certain limits or are found cracked, and incorporating Modification No. 6/1581 to prevent future chafing damage. Modification No. 6/1581 consists of installing a preformed nylon shield around the area of each wing strut of the upper end closest to the wing. Accomplishment of the proposed inspection and modification as specified in the NPRM would be required in accordance with de Havilland Service Bulletin No. 6/342, dated February 23, 1976.

Interested persons have been afforded an opportunity to participate in the making of this amendment. No comments were received on the proposed rule or the FAA's determination of the cost to the public.

The FAA's Determination

After careful review of all available information related to the subject presented above, the FAA has determined that air safety and the public interest require the adoption of the AD as proposed except for minor editorial corrections. The FAA has determined that these minor corrections will not change the meaning of the AD and will not add any additional burden upon the public than was already proposed.

FAA's Aging Commuter Aircraft Policy

This AD is consistent with the FAA's aging commuter airplane policy. This policy simply states that reliance on repetitive inspections of critical areas on airplanes utilized in commuter service carries an unnecessary safety risk when a design change exists that could eliminate or, in certain instances, reduce the number of those critical inspections. The alternative to incorporating Modification No. 6/1581 on de Havilland DHC-6 series airplanes would be relying on repetitive inspections to detect damaged wing struts.

Cost Impact

The FAA estimates that 169 airplanes in the U.S. registry will be affected by this AD, that it will take approximately 8 workhours per airplane to accomplish the required action, and that the average labor rate is approximately $60 an hour. Parts cost approximately $150 per airplane. Based on these figures, the total cost impact of the AD on U.S. operators is estimated to be $106,470. This figure is based upon the presumption that no affected airplane owner/operator has incorporated Modification No. 6/1581.

De Havilland has informed the FAA that enough parts have been distributed to equip approximately 11 of the affected airplanes. Presuming that each set of parts is incorporated on an affected airplane, the cost impact upon U.S. operators/owners would be reduced by $6,930 from $106,470 to $99,540.

Regulatory Impact

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 copy of the final evaluation prepared for this action is contained in the Rules Docket. A copy of it may be obtained by contacting 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 USC 106(g), 40113, 44701.

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