AD 97-13-05

This amendment adopts a new airworthiness directive (AD), applicable to certain Fokker Model F28 Mark 0100 series airplanes, that requires loosening certain nuts on the horizontal stabilizer control unit (HSCU) to reduce stress on bolts; a one-time inspection of certain bolts on the HSCU to detect cracking, and replacement, if necessary; application of corrosion protection to these bolts; and reassembly and reidentification of the modified HSCU. This amendment is prompted by reports indicating that stress corrosion, resulting from overtightening of nuts on these bolts, has caused some of these bolts to crack and fail. The actions specified by this AD are intended to prevent failure of these bolts because of stress corrosion cracking which, if not corrected, could lead to loss of control of the horizontal stabilizer and reduced controllability of the airplane.

Final rule

97-13-05 FOKKER: Amendment 39-10051. Docket 96-NM-154-AD.
Applicability: Model F28 Mark 0100 series airplanes, as listed in Fokker Service Bulletin SBF100-27-069, dated January 1, 1996; certificated in any category.

NOTE 1: This AD applies to each airplane identified in the preceding applicability provision, regardless of whether it has been otherwise 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: Requiredas indicated, unless accomplished previously.

To prevent failure of the lower bolts that join the dog-links to the piston of the horizontal stabilizer control unit (HSCU) because of stress corrosion cracking, which could result in loss of control of the horizontal stabilizer and reduced controllability of the airplane, accomplish the following:

(a) Within 3 months after the effective date of this AD, loosen the nut [part number (P/N) MS17825-10] on each lower bolt (P/N 23233-1) that joins the dog-links to the piston of the HSCU, in accordance with Part 1 of the Accomplishment Instructions of Fokker Service Bulletin SBF100- 27-069, dated January 1, 1996, as revised by Part 1 of Fokker Service Bulletin Change Notification SBF100-27-069/01, dated January 8, 1996; and Part A of the Accomplishment Instructions of Menasco Aerospace Ltd. Service Bulletin 23100-27-19, dated November 10, 1995.

(b) Within 6 months after the effective date of this AD, inspect each lower bolt (P/N23233-1) that joins the dog-links to the pistons of the HSCU to detect cracking and failure, in accordance with Part 2 of the Accomplishment Instructions of Fokker Service Bulletin SBF100-27- 069, dated January 1, 1996, as revised by Part 2 of Fokker Service Bulletin Change Notification SBF100-27-069/01, dated January 8, 1996; and Part B of the Accomplishment Instructions of Menasco Aerospace Ltd. Service Bulletin 23100-27-19, dated November 10, 1995.

(1) If no cracking or failure is detected, prior to further flight, apply corrosion protection to each bolt, and reassemble and reidentify the HSCU, in accordance with Part 2 of the Accomplishment Instructions of Fokker Service Bulletin SBF100-27-069, dated January 1, 1996, as revised by Part 2 of Fokker Service Bulletin Change Notification SBF100-27-069/01, dated January 8, 1996; and Part B of the Accomplishment Instructions of Menasco Aerospace Ltd. Service Bulletin 23100-27-19, dated November 10, 1995.

(2) If any cracking or failure is detected, prior to further flight, replace the discrepant bolt with a serviceable bolt, apply corrosion protection to each serviceable bolt, and reassemble and identify the HSCU, in accordance with Part 2 of the Accomplishment Instructions of Fokker Service Bulletin SBF100-27-069, dated January 1, 1996, as revised by Part 2 of Fokker Service Bulletin Change Notification SBF100-27-069/01, dated January 8, 1996; and Part B of the Accomplishment Instructions of Menasco Aerospace Ltd. Service Bulletin 23100-27-19, dated November 10, 1995.

(c) For airplanes having serial numbers 11500, 11505, and 11511: Within 6 months after the effective date of this AD, reidentify the HSCU in accordance with Part 3 of the Accomplishment Instructions of Fokker Service Bulletin SBF100-27-069, dated January 1, 1996.

(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, Standardization Branch, ANM-113, FAA, Transport Airplane Directorate. 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 2: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Standardization Branch, ANM-113.

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

(f) The actions shall be done in accordance with Fokker Service Bulletin SBF100-27-069, dated January 1, 1996, as revised by Fokker Service Bulletin Change Notification SBF100-27- 069/01, dated January 8, 1996; and Menasco Aerospace Ltd. Service Bulletin 23100-27-19, dated November 10, 1995. 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 Services B.V., Technical Support Department, P.O. Box 75047, 1117 ZN Schiphol Airport, The Netherlands. 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.

(g) This amendment becomes effective on August 1, 1997.

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 certain Fokker Model F28 0100 series airplanes was published in the Federal Register on November 8, 1996 (61 FR 57832). That action proposed to require loosening of nuts on lower bolts that join the dog-links to the pistons of the horizontal stabilizer control unit (HSCU); a one-time inspection of these bolts to detect cracking, and replacement of discrepant bolts with serviceable bolts; application of corrosion protection to these bolts; and reassembly and reidentification of the HSCU that has been modified. (Some airplanes were modified on the production line, but the HSCU was not reidentified. That action proposes to require that the HSCU on those airplanes also be reidentified.)

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 proposal and remarks, "However, we seek the FAA to ensure that the change in stress loading of the certain bolts does not result in a change to the integrity of the HSCU that could cause it to become jammed or fail in some manner that could be hazardous if it happened in flight." The FAA has determined that the change does not affect the structural integrity of the HSCU, since the bolts are loaded in shear not tension. No change to the final rule is required.

Conclusion
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.

Cost Impact
The FAA estimates that 125 Fokker Model F28 Mark 0100 series airplanes of U.S. registry will be affected by this AD, that it will take approximately 5 work hours per airplane to accomplish the required loosening of nuts, and that the averagelabor rate is $60 per work hour. Based on these figures, the cost impact of the loosening of nuts on U.S. operators is estimated to be $37,500, or $300 per airplane.

The FAA also estimates that it will take approximately 6 work hours per airplane to accomplish the required inspection, apply corrosion protection to the bolts, and reassemble and reidentify the HSCU. The average labor rate is $60 per work hour. Based on these figures, the cost impact of these actions on U.S. operators is estimated to be $45,000, or $360 per airplane.

There currently are no known airplanes of U.S. registry that will be required to accomplish the required reidentification of the HSCU because the HSCU was modified on the production line and not reidentified.

The cost impact figures discussed above are 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.

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 final evaluation has been prepared for this action and it is contained in the Rules Docket. A copy of it maybe 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 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 the following new airworthiness directive: