AD 94-07-13 ACTIVE

This amendment adopts a new airworthiness directive (AD), applicable to Fokker Model F-28 Mark 0100 series airplanes, that requires inspection, necessary repair, and modification of the engine mount shear shelf webs. This amendment is prompted by reports of interference between the engine mount shear shelf web and the fixed cowl mid and aft hooks, which caused fatigue cracks to occur in the web. The actions specified by this AD are intended to prevent fatigue cracking and other damage to the structure of the shear shelf web, which subsequently could lead to loss of the engine mounting structure.

Final rule

94-07-13 FOKKER: Amendment 39-8871. Docket 93-NM-148-AD.
Applicability: Model F-28 Mark 0100 series airplanes; having serial numbers 11244 to 11308 inclusive, 11310, 11312, 11313, 11314, 11316, 11321, 11328, and 11329; certificated in any category.

Compliance: Required as indicated, unless accomplished previously.

To prevent fatigue cracking and other damage to the engine mount shear shelf web, which subsequently could lead to loss of the engine mounting structure, accomplish the following:

(a) Prior to the accumulation of 12,000 total flight hours or within 90 days after the effective date of this AD, whichever occurs later, modify (reinforce) the engine mount shear shelf webs in accordance with Part 1 or Part 2, as applicable, of the Accomplishment Instructions of Fokker Service Bulletin SBF100-71-012, dated February 7, 1992.

(b) 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, Standardization Branch, FAA, Transport Airplane Directorate, ANM-113. Operators shall submit their requests through an appropriate FAA Principal Maintenance Inspector, who may add comments and then send it to the Manager, Standardization Branch, ANM-113.

NOTE: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Standardization Branch, ANM-113.

(c) 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.

(d) The modification shall be done in accordance with Fokker Service Bulletin SBF100-71-012, dated February 7, 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 Fokker Aircraft USA, Inc., 1199 North Fairfax Street, Alexandria, Virginia 22314. Copies may be inspected at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC.

(e) This amendment becomes effective on May 16, 1994.

A proposal to amend part 39 of the Federal Aviation Regulations to include an airworthiness directive (AD) that is applicable to Fokker Model F-28 Mark 0100 series airplanes was published in the Federal Register on October 21, 1993 (58 FR 54312). That action proposed to require inspection, necessary repair, and modification of the engine mount shear shelf webs.

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 supports the proposal.

Two commenters request that proposed paragraph (a)(1) be deleted from the rule. That paragraph proposed to require that a detailed visual inspection be conducted to detect cracking or other damage of the engine mount shear shelf webs around the areas of the fixed cowl aft- and mid-hook centerlines. These commenters contend that, since the modification required by paragraph (a)(2) reinforcesthe web and eliminates the interference problems, the inspection of this area should not be required to be accomplished. The FAA concurs. Since the interference problem that prompted this AD action has been found only in the area that is to be modified, and since the modification will prevent the interference problem and remove any evidence of damage, the FAA has determined that the proposed inspection is not necessary. Further, if an operator has already performed the proposed modification, the FAA finds that it would be an undue burden to require that the operator disassemble the modified area to accomplish an inspection of it. Additionally, the manufacturer and the one affected U.S. operator have advised the FAA that inspection of this area at intervals of 1,000 flight hours is already specified in the manufacturer's recommended maintenance program. In light of all of these factors, the FAA has revised the final rule to delete the requirement to inspect the subject area.

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 with the change previously described. The FAA has determined that this change will neither increase the economic burden on any operator nor increase the scope of the AD.

The FAA estimates that 20 airplanes of U.S. registry will be affected by this AD, that it will take approximately 120 work hours per airplane to accomplish the required actions, and that the average labor rate is $55 per work hour. Required parts will cost approximately $2,390 per airplane. Based on these figures, the total cost impact of the AD on U.S. operators is estimated to be $179,800, or $8,990 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. However, the FAA has been advised that all 20 affected U.S.-registered airplanes have been modified in accordance with the requirements of the AD as of December 1993. Therefore, there currently is no economic cost impact of this rule on U.S. operators.

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:

The service information referenced in this AD may be obtained from Fokker Aircraft USA, Inc., 1199 North Fairfax Street, Alexandria, Virginia 22314. This information may be examined at the Federal Aviation Administration (FAA), Transport Airplane Directorate, Rules Docket, 1601 Lind Avenue, SW., Renton, Washington; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC.

Mark Quam, Aerospace Engineer, Standardization Branch, ANM-113, FAA, Transport Airplane Directorate, 1601 Lind Avenue SW., Renton, Washington 98055-4056; telephone (206) 227-2145; fax (206) 227-1320.