AD 94-04-09

This amendment adopts a new airworthiness directive (AD), applicable to certain de Havilland Model DHC-8-100 and DHC-8-300 series airplanes, that requires inspections to detect breakage in the engine rear mount strut assemblies, and replacement of broken struts. This amendment also requires eventual replacement of all currently installed struts with new and/or reworked struts, as terminating action for the inspections. This amendment is prompted by several reports of failure of the engine rear mount struts, due to fracture at one of the rosette welds on the shank of the strut where full weld depth was not achieved during manufacture. The actions specified by this AD are intended to prevent fracture of the engine rear mount struts, which could reduce the structural integrity of the nacelle and engine support structure.

Final Rule

94-04-09 DE HAVILLAND, INC.: Amendment 39-8829. Docket 93-NM-149-AD.

Applicability: Model DHC-8-102 and -103 series airplanes, serial numbers 003 through 310 inclusive; and Model DHC-8-301, -311, and -314 series airplanes, serial numbers 100 through 311 inclusive, certificated in any category.

Compliance: Required as indicated, unless accomplished previously.

To prevent fracture of the engine rear mount struts, and subsequent reduced structural integrity of the nacelle and engine support structure, accomplish the following:

(a) Within 50 hours time-in-service after the effective date of this AD, perform a detailed visual inspection to detect breakage in the engine strut assemblies, part number 8711016-001, -003, -005, or -007, in accordance with De Havilland, Inc., Service Bulletin S.B. 8-71-17, dated April 3, 1992.

(1) If any broken strut is detected, prior to further flight, replace the broken strut with a new strut, part number 87110016-009, or a reworkedstrut, part number 8DK1763-001; Post-Modification 8/1763; in accordance with the service bulletin.

NOTE 1: The Post-Modification 8/1763 struts are either new struts, part number 87110016-009, or reworked struts, part number 8DK1763-001.

(2) If no broken strut is detected, repeat the inspection thereafter at intervals not to exceed 50 flight hours.

(b) Within 24 months after the effective date of this AD, replace all of the currently installed engine rear mount struts with new struts, part number 87110016-009, and/or reworked struts, part number 8DK1763-001; Post-Modification 8/1763; in accordance with de Havilland, Inc., Service Bulletin S.B. 8-71-17, dated April 3, 1992. This replacement constitutes terminating action for the repetitive inspection requirements of this AD.

(c) As of the effective date of this AD, no person shall install an engine rear mount strut, part number 8711016-001, -003, -005, or -007, on any airplane.

(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, New York Aircraft Certification Office (ACO), FAA, Engine and Propeller Directorate. Operators shall submit their requests through an appropriate FAA Principal Maintenance Inspector, who may add comments and then send it to the Manager, New York ACO.

NOTE 2: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the New York ACO.

(e) Special flight permits may be issued in accordance with Federal Aviation Regulations (FAR) 21.197 and 21.199 to operate the airplane to a location where the requirements of this AD can be accomplished.

(f) The inspections and replacements shall be done in accordance with de Havilland, Inc., Service Bulletin S.B. 8-71-17, dated April 3, 1992. 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., Garratt Boulevard, Downsview, Ontario M3K 1Y5, Canada. Copies may be inspected at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington; or at the FAA, Engine and Propeller Directorate, New York Aircraft Certification Office, 181 South Franklin Avenue, Room 202, Valley Stream, New York; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC.

(g) This amendment becomes effective on March 24, 1994.

A proposal to amend part 39 of the Federal Aviation Regulations to include an airworthiness directive (AD) that is applicable to certain de Havilland Model DHC-8-100 and DHC-8-300 series airplanes was published in the Federal Register on October 25, 1993 (58 FR 55031). That action proposed to require repetitive detailed visual inspections to detect breakage in the engine strut assemblies, and replacement of broken struts with new and/or reworked struts. That action also proposed to require eventual replacement of the currently installed struts with new and/or reworked struts; when accomplished, this replacement would terminate the need for the repetitive inspections.

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

The commenter supports the proposed rule.

After careful review of the available data, including the comment 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 125 airplanes of U.S. registry will be affected by this AD, that it will take approximately 16 work hours per airplane to accomplish the required actions, and that the average labor rate is $55 per work hour. Required parts will be provided by the manufacturer at no cost to the operators. Based on these figures, the total cost impact of the AD on U.S. operators is estimated to be $110,000, or $880 per airplane.

The total cost impact figure discussed above is based on assumptions that no operator has yet accomplished any of the requirements of this AD action, and that no operator would accomplish those actions in the future if this AD were not adopted.

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 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 14 CFR part 39 of the Federal Aviation Regulations 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 the following new airworthiness directive: