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###### Department of Transportation

###### Federal Aviation Administration

          - 14 CFR Part 39
          - [Docket No. 99-NM-368-AD]
          - RIN 2120-AA64

# AGENCY:

Federal Aviation Administration, DOT.

# ACTION:

Notice of proposed rulemaking (NPRM).

# SUMMARY:

This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain Saab Model SAAB 2000 series airplanes. This proposal would require repetitive detailed visual and dye penetrant inspections of the backup struts in the left and right nacelles to detect discrepancies; and corrective actions, if necessary. This proposal is prompted by issuance of mandatory continuing airworthiness information by a foreign civil airworthiness authority. The actions specified by the proposed AD are intended to prevent failure of the backup struts in the left and right nacelles due to fatigue cracking, which could result in loss of fail-safe redundancy in the design of the nacelle in terms of load capability. 

# DATES:

Comments must be received by June 9, 2000. 

# ADDRESSES:

Submit comments in triplicate to the Federal Aviation Administration (FAA), Transport Airplane Directorate, ANM-114, Attention: Rules Docket No. 99-NM-368-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056. Comments may be inspected at this location between 9 a.m. and 3 p.m., Monday through Friday, except Federal holidays. 

The service information referenced in the proposed rule may be obtained from Saab Aircraft AB, SAAB Aircraft Product Support, S-581.88, Linköping, Sweden. This information may be examined at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington. 

# FOR FURTHER INFORMATION CONTACT:

Norman B. Martenson, Manager, International Branch, ANM-116, FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (425) 227-2110; fax (425) 227-1149. 

# SUPPLEMENTARY INFORMATION:

## Comments Invited 

Interested persons are invited to participate in the making of the proposed 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 above. All communications received on or before the closing date for comments, specified above, will be considered before taking action on the proposed rule. The proposals contained in this notice may be changed in light of the comments received. 

Comments are specifically invited on the overall regulatory, economic, environmental, and energy aspects of the proposed 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 summarizing each FAA-public contact concerned with the substance of this proposal will be filed in the Rules Docket. 

Commenters wishing the FAA to acknowledge receipt of their comments submitted in response to this notice must submit a self-addressed, stamped postcard on which the following statement is made: “Comments to Docket Number 99-NM-368-AD.” The postcard will be date stamped and returned to the commenter. 

## Availability of NPRMs 

Any person may obtain a copy of this NPRM by submitting a request to the FAA, Transport Airplane Directorate, ANM-114, Attention: Rules Docket No. 99-NM-368-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056. 

## Discussion 

The Luftfartsverket (LFV), which is the airworthiness authority for Sweden, recently notified the FAA that an unsafe condition may exist on certain Saab Model SAAB 2000 series airplanes. The LFV advises that field experience has revealed fatigue cracking in the internal backup struts in the forward part of the nacelle structure. Such cracking was found in the area of the welded splices for the upper and lower attachment fittings. In the lower end of the attachment fittings, cracks were found near the local cut-out in the tube or areas adjacent to the welding, and in the upper area in the radius of the attachment fittings. On one occasion, fatigue cracks resulted in complete failure of the backup strut. Such fatigue cracking, if not corrected, could result in failure of the backup struts in the left and right nacelles, which could result in loss of fail-safe redundancy in the design of the nacelle in terms of load capability. 

## Explanation of Relevant Service Information 

The manufacturer has issued Saab Service Bulletin 2000-54-023, Revision 01, dated January 28, 2000, which describes procedures for repetitive detailed visual and dye penetrant inspections of the backup struts in the left and right nacelles to detect discrepancies; and corrective actions, if necessary. Descriptions of the two types of inspections are as follows: 
    - The initial detailed visual inspection includes the upper areas of the backup strut around the welding in the pipe and in the attachment fittings.
    - The initial dye penetrant inspection, using a Penetrant Type 1 (fluorescent dye) sensitivity level 2, includes the lower areas of the backup strut around the welding in the pipe and in the attachment fittings, and specifies taking special care to check the inside edge of the cutouts.

If any inspection reveals a failed backup strut, procedures include the following additional inspections of the engine mount surrounding structure: 
    - Detailed visual inspections of each engine mount strut and mounting       ( print page 30024)                          fittings, forward semi-circular collar/frame and aft beam, nacelle backup strut opposite side to the failed backup strut and attachment fittings at station 176/199, inboard and outboard upper and lower longerons of the nacelle, and upper and lower longerons at the attachment to the inboard and outboard upper and lower fittings of the nacelle.                
    - General visual inspections of the inner and outer side walls and side of the skin panels.

Discrepancies include fatigue cracking, a failed backup strut, and damage to the surrounding structure of the engine mount. Corrective actions include replacing any failed backup strut located in the hydraulic bay or electrical bay areas with a new backup strut, and performing additional inspections of the surrounding structure of the engine mount. 

The LFV classified this service bulletin as mandatory and issued Swedish airworthiness directive No. 1-150R1, dated January 31, 2000, in order to assure the continued airworthiness of these airplanes in Sweden. 

## FAA's Conclusions 

This airplane model is manufactured in Sweden and is type certificated for operation in the United States under the provisions of section 21.29 of the Federal Aviation Regulations (14 CFR 21.29) and the applicable bilateral airworthiness agreement. Pursuant to this bilateral airworthiness agreement, the LFV has kept the FAA informed of the situation described above. The FAA has examined the findings of the LFV, 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 Proposed 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, the proposed AD would require accomplishment of the actions specified in the service bulletin described previously, except as described below. 

## Differences Between Proposed AD and Service Bulletin 

Operators should note that, although the service bulletin specifies that the manufacturer may be contacted for repair instructions for certain damage conditions, this proposed AD would require the repair of those conditions to be accomplished in accordance with a method approved by either the FAA or the LFV (or its delegated agent). In light of the type of repair that would be required to address the identified unsafe condition, and in consonance with existing bilateral airworthiness agreements, the FAA has determined that a repair approved by either the FAA or the LFV would be acceptable for compliance with this proposed AD. 

## Interim Action 

This is considered to be interim action until final action is identified, at which time the FAA may consider further rulemaking. 

## Cost Impact 

The FAA estimates that 3 airplanes of U.S. registry would be affected by this proposed AD, that it would take approximately 8 work hours per airplane to accomplish the proposed inspections, and that the average labor rate is $60 per work hour. Based on these figures, the cost impact of the proposed AD on U.S. operators is estimated to be $1,440, or $480 per airplane, per inspection cycle. 

The cost impact figure discussed above is based on assumptions that no operator has yet accomplished any of the proposed 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 proposed herein would not have a substantial direct effect 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, it is determined that this proposal would not have federalism implications under Executive Order 13132. 

                    For the reasons discussed above, I certify that this proposed regulation (1) is not a “significant regulatory action” under Executive Order 12866; (2) is not a “significant rule” under the DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and (3) if promulgated, 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 copy of the draft regulatory evaluation prepared for this action is contained in the Rules Docket. A copy of it may be obtained by contacting the Rules Docket at the location provided under the caption                     **ADDRESSES.**

# List of Subjects in 14 CFR Part 39

      - Air transportation
      - Aircraft
      - Aviation safety
      - Safety

## The Proposed Amendment 

Accordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration proposes to amend 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 

2. Section 39.13 is amended by adding the following new airworthiness directive:

**SAAB Aircraft AB:**                                 Docket 99-NM-368-AD.                             

*Applicability:*                                 Model SAAB 2000 series airplanes, serial numbers -004 through -063 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 (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:*                                 Required as indicated, unless accomplished previously.                             

To prevent failure of the backup struts in the left and right nacelles due to fatigue cracking, which could result in loss of fail-safe redundancy in the design of the nacelle in terms of load capability, accomplish the following: 

Repetitive Inspections 

(a) For airplanes on which the dye penetrant inspection of the backup struts in the left and right nacelles specified in Saab Alert Service Bulletin 2000-A54-022, dated 

October 27, 1999, has not been accomplished prior to the effective date of this AD: 

Within 200 flight hours after the effective date of this AD, accomplish paragraphs (b)(1) and (b)(2) of this AD in accordance with the Accomplishment Instructions of Saab Service Bulletin 2000-54-023, Revision 01, dated January 28, 2000. 

                                (b) For airplanes on which the dye penetrant inspection of the backup struts in the left and right nacelle specified in Saab Alert Service Bulletin 2000-A54-022, dated October 27, 1999, has been accomplished prior to the effective date of this AD: Within 450 flight hours after the effective date of this AD, accomplish paragraphs (b)(1) and (b)(2) of this AD in accordance with the Accomplishment Instructions of Saab Service Bulletin 2000-54-023, Revision 01, dated January 28, 2000.                                       ( print page 30025)    

(1) Perform a detailed visual inspection of the upper areas of the backup strut around the welding in the pipe and in the attachment fittings to detect any discrepancy (including fatigue cracking or a failed backup strut) by accomplishing all actions specified in paragraph B.(1) of the Accomplishment Instructions of the service bulletin, in accordance with that service bulletin. Repeat the detailed visual inspection thereafter at intervals not to exceed 450 flight hours. 

# 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 (                                    *e.g.,*                                     mirror, magnifying lenses) may be used. Surface cleaning and elaborate access procedures may be required.”                                

(2) Perform a dye penetrant inspection, using Penetrant Type 1 (fluorescent dye) sensitivity level 2, of the lower areas of the backup strut around the welding in the pipe and in the attachment fittings to detect any discrepancy (including fatigue cracking or a failed backup strut) by accomplishing all actions specified in paragraphs B.(2) and B.(3) of the service bulletin, as applicable, in accordance with that service bulletin. 

(i) For airplanes on which all backup struts have accumulated less than 4,500 total flight hours as of the effective date of this AD, repeat the dye penetrant inspection thereafter at intervals not to exceed 1,650 flight hours, until any backup strut on the airplane has accumulated 4,500 total flight hours; then perform the repetitive inspection thereafter at the interval specified by paragraph (b)(2)(ii) of this AD. 

(ii) For airplanes on which any backup strut has accumulated 4,500 or more total flight hours as of the effective date of this AD, repeat the dye penetrant inspection thereafter at intervals not to exceed 900 flight hours. 

## Corrective Actions 

(c) If any discrepancy (including fatigue cracking, a failed backup strut, or damage to the surrounding structure of the engine mount) is detected during any inspection required by this AD: Prior to further flight, accomplish the applicable corrective actions (including performing additional inspections of the engine mount surrounding structure, and replacing any discrepant backup strut in the hydraulic or electrical bay areas with a new backup strut) specified by paragraph C. of the Accomplishment Instructions of Saab Service Bulletin 2000-54-023, Revision 01, dated January 28, 2000, in accordance with that service bulletin. For any repair condition for which the service bulletin specifies to contact the manufacturer for appropriate 

ACTION: Prior to further flight, repair in accordance with a method approved by either the Manager, International Branch, ANM-116, FAA, Transport Airplane Directorate; or the Luftfartsverket (LFV) (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 

(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, International Branch, ANM-116. Operators shall submit their requests through an appropriate FAA Principal Maintenance Inspector, who may 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 

(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. 

# Note 4:

The subject of this AD is addressed in Swedish airworthiness directive No. 1-150R1, dated January 31, 2000.

Issued in Renton, Washington, on May 4, 2000. 

Vi L. Lipski, 

Acting Manager, Transport Airplane Directorate, Aircraft Certification Service.

[FR Doc. 00-11723 Filed 5-9-00; 8:45 am] 

BILLING CODE 4910-13-U