AD 94-24-10

This amendment adopts a new airworthiness directive (AD), applicable to certain Saab Model SAAB SF340A and SAAB 340B airplanes, that requires repetitive inspections to detect cracking of the tray stop spindle and backrest spindle bosses on the inboard sections of certain seats; and replacement of the inboard sections, if necessary. This amendment also requires repair and identification of the modification plate, which would terminate the requirement to inspect repetitively. This amendment is prompted by reports of fatigue cracking in the vicinity of the tray stop spindle and backrest spindle bosses, which could lead to excessive movement and eventual failure of the backrest on these seats during aft loading. The actions specified by this AD are intended to prevent failure of the backrest on these seats, which could inhibit emergency egress.

Final rule

94-24-10 SAAB AIRCRAFT AB: Amendment 39-9083. Docket 94-NM-23-AD.
Applicability: Model SAAB SF340A airplanes having serial numbers 004 through 159 inclusive, and Model SAAB 340B airplanes having serial numbers 160 through 330 inclusive; equipped with Flight Equipment and Engineering Limited (FEEL) Model 121 series seats listed in FEEL Service Bulletin 25-20-1294, Revision 1, dated May 1993, and FEEL Service Bulletin 25-20-1287, Revision 3, dated March 1993; 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 use the authority provided in paragraph (c) to request approval from the FAA. This approval may address either no action, if thecurrent configuration eliminates the unsafe condition; or different actions necessary to address the unsafe condition described in this AD. Such a request should include an assessment of the effect of the changed configuration on the unsafe condition addressed by this AD. In no case does the presence of any modification, alteration, or repair remove any airplane from the applicability of this AD.

Compliance: Required as indicated, unless accomplished previously.

To prevent failure of the backrest on these seats, which could inhibit emergency egress, accomplish the following:

(a) Within 28 days after the effective date of this AD, perform a detailed visual inspection to detect cracking of the tray stop spindle and backrest spindle bosses of the inboard section of the seat, in accordance with FEEL Service Bulletin 25-20-1287, Revision 3, dated March 1993.

(1) If no cracking is found, or if cracking is found that does not penetrate the shear web, repeat the inspection of that seat thereafter at intervals not to exceed 150 hours time-in- service until the requirements or paragraph (b) of this AD are accomplished.

(2) If any cracking is found that penetrates the shear web, prior to further flight, replace the inboard section (up to issue 12), and identify the modification plate with "25-20-1287A," in accordance with the service bulletin. Thereafter, repeat the inspection at intervals not to exceed 150 hours time-in-service until the requirements of paragraph (b) of the AD are accomplished.

(b) Within 6 months after the effective date of this AD, repair and identify the modification plate with "25-20-1294," in accordance with FEEL Service Bulletin 25-20-1294, Revision 1, dated May 1993. Accomplishment of the actions required by this paragraph constitutes terminating action for the requirements of this AD.

(c) 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.

(d) 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.

(e) The inspection shall be done in accordance with FEEL Service Bulletin 25-20-1287, Revision 3, dated March 1993. The repair and identification shall be done in accordance with FEEL Service Bulletin 25-20-1294, Revision 1, dated May 1993, which contains the following list ofeffective pages:

Page Number
Revision Level
Shown on Page
Date
Shown on Page
1-3, 19
1
May 1993
4-18
Basic
March 1993

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 Flight Equipment and Engineering Limited, Technical Manager, Nissen House, Grovebury Road, Leighton Buzzard, Bedfordshire LU7 8TB, United Kingdom. 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.

(f) This amendment becomes effective on January 6, 1995.

FOR FURTHER INFORMATION CONTACT: 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.

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 Saab Model SAAB SF340A and SAAB 340B airplanes, equipped with Flight Equipment And Engineering Limited Model 121 series seats, was published in the Federal Register on May 3, 1994 (59 FR 22771). That action proposed to require repetitive inspections to detect cracking of the tray stop spindle and backrest spindle bosses on the inboard sections of certain seats; and replacement of the inboard sections, if necessary. It also proposed to require repair and identification of the modification plate, which would terminate the requirement to inspect repetitively.

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 has no objections to the proposal, but questions the accuracy of thedescription of the point of failure, as described in the preamble to the notice. The preamble stated, "Cracking in this area may weaken the machined component that attaches the backrest of the seats to the main spars of the airplane and may lead to excessive movement and eventual failure of the backrest on these seats during aft loading" (highlighting added). The commenter implies that it is not accurate to state that the failure point is where the seat backrests attach to the main spar of the airplane. The FAA has reconsidered its previous description and concurs that clarification is warranted. The FAA finds that the following wording comprises a more accurate description:

"Cracking in this area may eventually weaken the seat section such that the spindles attaching the table and seat back to the seat section may break free during crash loads or normal loads. This condition, if not corrected, could result in failure of the backrest of these seats, which could inhibit emergency egress."

This clarification of the description of the failure scenario in no way alters the basis for issuance of this AD or the unsafe condition addressed by it.

As a result of recent communications with the Air Transport Association (ATA) of America, the FAA has learned that, in general, some operators may misunderstand the legal effect of AD's on airplanes that are identified in the applicability provision of the AD, but that have been altered or repaired in the area addressed by the AD. Under these circumstances, at least one operator appears to have incorrectly assumed that its airplane was not subject to an AD. On the contrary, all airplanes identified in the applicability provision of an AD are legally subject to the AD. If an airplane has been altered or repaired in the affected area in such a way as to affect compliance with the AD, the owner or operator is required to obtain FAA approval for an alternative method of compliance with the AD, in accordance withthe paragraph of each AD that provides for such approvals. A note has been added to this final rule to clarify this requirement.

The FAA has recently reviewed the figures it has used over the past several years in calculating the economic impact of AD activity. In order to account for various inflationary costs in the airline industry, the FAA has determined that it is necessary to increase the labor rate used in these calculations from $55 per work hour to $60 per work hour. The economic impact information, below has been revised to reflect this increase in the specified hourly labor rate.

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

The FAA estimates that 73 airplanes of U.S. registry will be affected by this AD, that it will take approximately 2 work hours per seat to accomplish the required actions, and that the average labor rate is $60 per work hour. There are usually 34 seats per airplane. Required parts will be provided by the manufacturer at no cost to the operator. Based on these figures, the total cost impact of the AD on U.S. operators is estimated to be $297,840, or $4,080 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.

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. 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: