AD 97-04-08

This amendment adopts a new airworthiness directive (AD), applicable to certain Fokker Model F27 Mark 050, 100, 200, 300, 400, 600, and 700 series airplanes, that requires an ultrasonic inspection to determine if certain tubes are installed in the drag stay units of the main landing gear (MLG), and various follow-on actions. This amendment is prompted by a report that, due to fatigue cracking from an improperly machined radius of the inner tube, a drag stay broke, and, consequently, lead to the collapse of the MLG during landing. The actions specified by this AD are intended to prevent such fatigue cracking, which could result in reduced structural integrity or collapse of the MLG.

Final rule

97-04-08 FOKKER: Amendment 39-9932. Docket 96-NM-32-AD.

Applicability: Model F27 Mark 050, 100, 200, 300, 400, 600, and 700 series airplanes, equipped with Dowty Aerospace main landing gear (MLG) drag stay units (DSU) having part number (P/N) 200684001, 200261001, or 200485001; certificated in any category.

NOTE 1: 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 (e) 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 accomplished previously.

To prevent fatigue cracking in drag stay unit of the MLG, which could result in reduced structural integrity or collapse of the MLG, accomplish the following:

(a) Within 60 days after the effective date of this AD, perform an ultrasonic inspection to determine if a tube having part number (P/N) 200485300 with a straight bore, or a tube having P/N 200259300 with a change in section (stepped bore), is installed on the DSU's of the MLG, in accordance with Fokker Service Bulletin F27/32-167, dated November 19, 1993 (for Model F27 Mark 100, 200, 300, 400, 600, and 700 series airplanes), or Fokker Service Bulletin SBF50-32-029, dated February 11, 1994 (for Model F27 Mark 050 series airplanes), as applicable.

NOTE 2: Fokker Service Bulletin F27/32-167 references Dowty Service Bulletins 23-169B and 32-82W; and Fokker Service Bulletin SBF50-32-029 references Dowty Service Bulletin F50-32-50; as additional sources of service information for procedures to accomplish the actions specified in this AD.

(b) For all airplanes: If any tube having P/N 200485300 with a straight bore is found installed during the inspection required by paragraph (a) of this AD, prior to further flight, reidentify it in accordance with Fokker Service Bulletin F27/32-167, dated November 19, 1993 (for Model F27 Mark 100, 200, 300, 400, 600, and 700 series airplanes); or Fokker Service Bulletin SBF50-32-029, dated February 11, 1994 (for Model F27 Mark 050 series airplanes); as applicable.

(c) For Model F27 Mark 50 series airplanes: If any tube having P/N 200259300 with a change in section (stepped bore) is found installed during the inspection required by paragraph (a) of this AD, prior to further flight, replace the DSU with a new or serviceable DSU having P/N 200684004, in accordance with Fokker Service Bulletin SBF50-32-029, dated February 11, 1994.

(d) For F27 Mark 100, 200, 300, 400, 600, and 700 series airplanes: If any tube having P/N 200259300 with a change in section (stepped bore) is found installed during the inspection required by paragraph (a) of this AD, prior to further flight, re-identify the DSU in accordance with Fokker Service Bulletin F27/32-167, dated November 19, 1993. Following accomplishment of the re-identification, prior to further flight, perform an ultrasonic inspection to detect cracks in the re-identified DSU's, in accordance with that service bulletin.

(1) For airplanes equipped with any DSU re-identified as P/N 200684003, 200261003, or 200485003: If no crack is detected, no further action is required by this AD.

(2) For airplanes equipped with any DSU re-identified as P/N 200684002, 200261002, or 200485002: If no crack is detected, accomplish paragraphs (d)(2)(i) and (d)(2)(ii) of this AD.

(i) Repeat the ultrasonic inspection required by paragraph (d) of this AD thereafter at intervals not to exceed 1,500 flight cycles.

(ii) At the next MLG overhaul, but no later than 12,000 flight cycles after the effective date of this AD, rework and re-identify the DSU again, or replace the DSU with a re-identified DSU, in accordance with the service bulletin. Accomplishment of the rework and re-identification, or replacement constitutes terminating action for the repetitive inspection requirements of this AD.

(3) If any crack signal indication of any DSU tube is greater than or equal to 80 percent, prior to further flight, replace the DSU with a re-identified DSU, in accordance with the service bulletin.

(4) If any crack signal indication of any DSU tube is greater than or equal to 1 percent but less than 80 percent, accomplish paragraphs (d)(4)(i) and (d)(4(ii) of this AD.

(i) Repeat the ultrasonic inspection required by paragraph (d) of this AD thereafter at intervals not to exceed 1,500 flight cycles.

(ii) At the next MLG overhaul, but no later than 12,000 flight cycles after the effective date of this AD, replace the DSU with a re-identified DSU, in accordance with the service bulletin. Accomplishment of the replacement constitutes terminating action for the repetitive inspection requirements of this AD.

(e) 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 3: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Standardization Branch, ANM-113.

(f) Special flight permits may be issued in accordance with sections 21.197 and 21.199 of the Federal AviationRegulations (14 CFR 21.197 and 21.199) to operate the airplane to a location where the requirements of this AD can be accomplished.

(g) The actions shall be done in accordance with Fokker Service Bulletin F27/32-167, dated November 19, 1993; or Fokker Service Bulletin SBF50-32-029, dated February 11, 1994; as applicable. 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.

(h) This amendment becomes effective on March 28, 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 F27 Mark 050, 100, 200, 300, 400, 600, and 700 series airplanes was published in the Federal Register on October 31, 1996 (61 FR 56170). That action proposed to require an ultrasonic inspection to determine if certain tubes are installed on the DSU s of the MLG, and various follow-on actions.

Interested persons have been afforded an opportunity to participate in the making of this amendment. No comments were submitted in response to the proposal or the FAA's determination of the cost to the public.

Conclusion
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 10 Model F27 Mark 050, 100, 200, 300, 400, 600, and 700 series airplanes of U.S. registry will be affected by this AD, that it will take approximately 2 work hours per airplane to accomplish the required inspection, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of the inspection required by this AD on U.S. operators is estimated to be $1,200, or $120 per airplane. This cost impact figure 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.

There currently are no Fokker Model F27 Mark 050 series airplanes on the U.S. Register that will require the inspection of the DSU. The only airplanes that will require this inspection are currently operated by non-U.S. operators under foreign registry; therefore, they are not directly affected by this AD action. However, the FAA considers that inclusion of these airplanes in the applicability of this rule is necessary to ensure that the unsafe condition is addressed in the event that any of these airplanes are imported and placed on the U.S. Register in the future.

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 beenprepared 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 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: