AD 99-27-03

This amendment adopts a new airworthiness directive (AD), applicable to certain Fokker Model F27 Mark 050 series airplanes. This action requires repetitive inspections of the connections between certain ribs and stringers of the wing skins to detect loose or missing rivets or gaps, and corrective actions, if necessary. This action also requires eventual modification of the rib-stringer connection, which terminates the repetitive inspections. This amendment is prompted by issuance of mandatory continuing airworthiness information by a foreign civil airworthiness authority. The actions specified in this AD are intended to prevent fatigue cracking in the skin and stringers, which could result in reduced structural integrity of the wings.

Final rule; request for comments

99-27-03 FOKKER: Amendment 39-11484. Docket 99-NM-235-AD. Issued December 21, 1999.

Applicability: Model F27 Mark 050 series airplanes, serial numbers 20103 through 20298 inclusive; 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 the skin and stringers, which could result in reduced structural integrity of the wings, accomplish the following:

(a) Perform a detailed visual inspection of the connections between ribs 11260, 11860, 12660, and 13460, and stringers 4, 5, 6, and 7 of the top and bottom wing skins to detect loose or missing rivets or gaps, in accordance with Part 1 of Fokker Service Bulletin SBF50-57-019, dated February 27, 1998; at the time specified in paragraph (a)(1), (a)(2), (a)(3), or (a)(4) of this AD, as applicable. Repeat the inspection thereafter at intervals not to exceed 2,500 flight cycles.

(1) For airplanes that have accumulated less than 15,000 total flight cycles as of the effective date of this AD: Inspect prior to the accumulation of 15,000 total flight cycles, or within 12 months after the effective date of this AD, whichever occurs later.

(2) For airplanes that have accumulated 15,000 total flight cycles or more but less than 20,000 total flight cycles as of the effective date of this AD: Inspect within 12 months after the effective date of this AD.

(3) For airplanes that have accumulated 20,000 total flight cycles or more but less than 25,000 total flight cycles as of the effective date of this AD: Inspect within 6 months after the effective date of this AD.

(4) For airplanes that have accumulated 25,000 total flight cycles or more as of the effective date of this AD: Inspect within 3 months after the effective date of this AD. NOTE 2: For the purposes of this AD, a detailed visual inspection is defined as: "An intensive visual examination of a specific structural area, system, installation, or assembly to detect damage, failure, or irregularity. Available lighting is normally supplemented with a direct source of good lighting at intensity deemed appropriate by the inspector. Inspection aids such as mirror, magnifying lenses, etc. may be used. Surface cleaning and elaborate access procedures may be required."

(b) Except as provided by paragraph (d) of this AD, if no loose or missing fastener, or no gap is found during any inspection required by paragraph (a) of this AD, prior to the accumulation of 40,000 total flight cycles, or within 18 months after the effective date of this AD, whichever occurs later, modify the rib-stringer connections (i.e., reaming of rivet holes, rotating probe eddy current inspections, corrective actions, and installation of connecting angles) in accordance with Part 2 of the Accomplishment Instructions of Fokker Service Bulletin SBF50-57-019, dated February 27, 1998. Accomplishment of the actions required by this paragraph constitutes terminating action for the repetitive inspection requirements of paragraph (a) of this AD.

(c) If any loose or missing fastener, or any gap is found during any inspection required by paragraph (a) of this AD, prior to further flight, accomplish the actions specified inparagraph (c)(1), (c)(2), or (c)(3) of this AD in accordance with Fokker Service Bulletin SBF50-57-019, dated February 27, 1998.

(1) Accomplish the modification specified in paragraph (b) of this AD.
(2) Except as provided by paragraph (d) of this AD, accomplish the temporary repair (i.e., surface probe eddy current inspection, repair, and installation of a shim and new blind rivets) in accordance with Part 3 of the Accomplishment Instructions of the service bulletin. Within 500 flight cycles after accomplishment of this temporary repair, accomplish the modification specified in paragraph (b) of this AD.
(3) Except as provided by paragraph (d) of this AD, accomplish the temporary repair (i.e., surface probe eddy current inspection, repair, and installation of connecting angles) in accordance with Part 4 of the Accomplishment Instructions of the service bulletin. Within 2,500 flight cycles after accomplishment of this temporary repair, accomplish the modification specified in paragraph (b) of this AD.

(d) If any discrepancy is found during any inspection required by paragraph (a), (b), or (c) of this AD; and Fokker Service Bulletin SBF50-57-019, dated February 27, 1998, specifies to contact Fokker for appropriate action: Prior to further flight, repair in accordance with either a method approved by the Manager, International Branch, ANM-116, FAA, Transport Airplane Directorate, or the Rijksluchtvaartdienst (RLD) (or its delegated agent). For a repair method to be approved by the Manager, International Branch, ANM-116, as required by this paragraph, the Manager's approval letter must specifically reference this AD.

Alternative Methods of Compliance
(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, International Branch, ANM-116. Operators shall submit their requests through an appropriate FAA Principal Maintenance Inspector, whomay add comments and then send it to the Manager, International Branch, ANM-116.

NOTE 3: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the International Branch, ANM-116.

Special Flight Permits
(f) 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.

Incorporation by Reference
(g) Except as provided by paragraph (d) of this AD, the actions shall be done in accordance with Fokker Service Bulletin SBF50-57-019, dated February 27, 1998. 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., P.O. Box 231, 2150 AE Nieuw-Vennep, 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.

NOTE 4: The subject of this AD is addressed in Dutch airworthiness directive 1998-023/2, dated October 30, 1998. (h) This amendment becomes effective on January 13, 2000.

The Rijksluchtvaartdienst (RLD), which is the airworthiness authority for the Netherlands, notified the FAA that an unsafe condition may exist on certain Fokker Model F27 Mark 050 series airplanes. The RLD advises that rivet heads were missing at the rib-to-stringer connections of both the upper and lower wing skin. Investigation revealed that understrength rivets were used in the affected connections. Such deficient connections reduce the static buckling strength of the wing skin and may cause fretting of the stringer. This condition, if not corrected, could result in fatigue cracking in the skin and stringers, which could result in reduced structural integrity of the wings.

Explanation of Relevant Service Information
Fokker has issued Service Bulletin SB50-57-019, dated February 27, 1998, which describes procedures for repetitive detailed visual inspections of the connections between ribs 11260, 11860, 12660, and 13460, and stringers 4, 5, 6, and 7 of the top and bottom wing skins to detect loose or missing rivets or gaps. The service bulletin also describes procedures for modification of the rib-stringer connection. The modification involves reaming the original rivet holes of the rib-stringer connections, performing a rotating probe eddy current inspection to detect cracks of these rivet holes, performing corrective actions for cases where cracking is detected, and installing connecting angles between the stringers and ribs. The corrective actions include reaming the diameter of the rivet hole, performing a surface probe eddy current inspection to detect cracks of the surrounding of each rivet hole, drilling out rivets, removing connecting angles, and repairing angles, as applicable. Accomplishment of the modification eliminates the need for the repetitive inspections. For cases where cracking is detected during the visual inspection, the service bulletin describes procedures for accomplishing either of the following temporary repairs and eventual modification of the rib-stringer connection (described previously): Performing a surface probe eddy current inspection to detect cracks in the surrounding of the rib-stringer connection in the area of the gap and/or loose or missing rivets; and installing a shim between the rib-girder and the stringer and new blind rivets, and repairing the crack; as applicable. Performing a surface probe eddy current inspection to detect cracks in the surrounding of the rib-stringer connection in the area of the gap and/or loose or missing rivet; and installing connecting angles and repairing the crack; as applicable. Accomplishment of the actions specified in the service bulletin is intended to adequately address the identified unsafe condition. The RLD classified this service bulletin as mandatory and issued Dutch airworthiness directive BLA 1998-023/2, dated October 30, 1998, in order to assure the continued airworthiness of these airplanes in the Netherlands.

FAA's Conclusions
This airplane model is manufactured in the Netherlands and is type certificated for operation in the United States under the provisions of section 21.29 of the Federal Aviation Regulations (14 CFR 21.19) and the applicable bilateral airworthiness agreement. Pursuant to this bilateral airworthiness agreement, the RLD has kept the FAA informed of the situation described above. The FAA has examined the findings of the RLD, reviewed all available information, and determined that AD action is necessary for products of this type design that are certificated for operation in the United States.

Explanation of Requirements of the Rule
Since an unsafe condition has been identified that is likely to exist or develop on other airplanes of the same type design registered in the United States, this AD requires accomplishment of the actions specified in the service bulletin described previously, except as discussed below.

Differences Between Proposed Rule and Service Bulletin
Operators should note that, although the service bulletin specifies that the manufacturer may be contacted for disposition of certain repair conditions, this AD requires the repair of those conditions to be accomplished in accordance with a method approved by the FAA, or the RLD (or its delegated agent). In light of the type of repair required to address the identified unsafe condition, and in consonance with existing bilateral airworthiness agreements, the FAA has determined that, for this AD, a repair approved by either the FAA or the RLD is acceptable for compliance with this AD.

Cost Impact
None of the airplanes affected by this action are on the U.S. Register. All airplanes included in the applicability of this rule currently are operated by non-U.S. operators under foreign registry; therefore, they are not directly affected by this AD action. However, the FAA considers that this rule is necessary to ensure that the unsafe condition is addressed in the event that any of these subject airplanes are imported and placed on the U.S. Register in the future.

Should an affected airplane be imported and placed on the U.S. Register in the future, it would require approximately 11 work hours to accomplish the required visual inspection, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of the visual inspection required by this AD would be $660 per airplane, per inspection cycle.

Should an affected airplane be imported and placed on the U.S. Register in the future, it would require approximately between 80 and 116 work hours to accomplish the required modification, at an average labor rate of $60 per work hour. Required parts would cost approximately $11,850 per airplane. Based on these figures, the cost impact of the modification required by this AD would be between $16,650 and $18,810 per airplane.

Determination of Rule's Effective Date
Since this AD action does not affect any airplane that is currently on the U.S. register, it has no adverse economic impact and imposes no additional burden on any person. Therefore, prior notice and public procedures hereon are unnecessary and the amendment may be made effective in less than 30 days after publication in the Federal Register.

Comments Invited
Although this action is in the form of a final rule and was not preceded by notice and opportunity for public comment, comments are invited on this rule. Interested persons are invited to comment on this rule by submitting such written data, views, or arguments as they may desire. Communications shall identify the Rules Docket number and be submitted in triplicate to the address specified under the caption "ADDRESSES." All communications received on or before the closing date for comments will be considered, and this rule may be amended in light of the comments received. Factual information that supports the commenter's ideas and suggestions is extremely helpful in evaluating the effectiveness of the AD action and determining whether additional rulemaking action would be needed.

Comments are specifically invited on the overall regulatory, economic, environmental, and energy aspects of the rule that might suggest a need to modify the rule. All comments submitted will be available, both before and after the closing date for comments, in the Rules Docket for examination by interested persons. A report that summarizes each FAA-public contact concerned with the substance of this AD will be filed in the Rules Docket.

Commenters wishing the FAA to acknowledge receipt of their comments submitted in response to this rule must submit a self-addressed, stamped postcard on which the following statement is made: "Comments to Docket Number 99-NM-235-AD." The postcard will be date stamped and returned to the commenter.

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 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: