AD 96-08-06

This amendment adopts a new airworthiness directive (AD), applicable to certain Saab Model SAAB SF340A and SAAB 340B series airplanes, that requires visual and dye penetrant inspection(s) to detect cracks of the nose rib of the rudder, and stop drilling and blending of minor cracks. This amendment also requires replacement of the nose rib with a new nose rib and reinforcement of the nose rib, if extensive cracking is detected or if an operator elects to terminate the repetitive inspections. This amendment is prompted by the result of an inspection that revealed a cracked nose rib on the front spar of the rudder due to vibration-related stress. The actions specified by this AD are intended to prevent such stress and cracking, which could result in the deformation of the nose rib; this condition may lead to friction and jamming between the fin and the rudder and subsequent reduced controllability of the airplane.

Final rule

96-08-06 SAAB AIRCRAFT AB: Amendment 39-9572. Docket 95-NM-121-AD.
Applicability: Model SAAB SF340A series airplanes having serial numbers (S/N) 004 through 159 inclusive, and Model SAAB 340B having S/N's 160 through 369 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 (b) 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 vibration-related stress and cracking and consequent deformation of the nose rib, which could result in friction and jamming between the fin and the rudder and subsequent reduced controllability of the airplane, accomplish the following:

(a) Prior to the accumulation of 2,400 total flight hours, or within 800 flight hours after the effective date of this AD, whichever occurs later, perform a visual and dye penetrant inspection to detect cracks of the nose rib of the rudder, in accordance with Saab Service Bulletin 340-55- 032, dated May 22, 1995.

(1) If no cracks are detected, repeat the inspection thereafter at intervals not to exceed 800 flight hours, or replace the nose rib with a new nose rib and reinforce it, in accordance with the service bulletin. Accomplishment of the replacement and reinforcement constitutes terminating action for this AD.

(2) If any minor crack[less than 25.4 mm (1.0 inch) long] is detected, prior to further flight, stop drill and blend the crack in accordance with the service bulletin. Repeat the inspection thereafter at intervals not to exceed 800 flight hours, or replace the nose rib with a new nose rib and reinforce it, in accordance with the service bulletin. Accomplishment of the replacement and reinforcement constitutes terminating action for this AD.

(3) If any extensive crack [greater than or equal to 25.4 mm (1.0 inch) long] is detected, prior to further flight, replace the nose rib with a new nose rib and reinforce it, in accordance with the service bulletin. Accomplishment of this replacement and reinforcement constitutes terminating action for this AD.

(b) 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.

(c) 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.

(d) The actions shall be done in accordance with Saab Service Bulletin 340-55-032, dated May 22, 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 SAAB Aircraft AB, SAAB Aircraft Product Support, S-581.88, Link ping, Sweden. 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.

(e) This amendment becomes effective on May 23, 1996.

FOR FURTHER INFORMATION CONTACT: Ruth Harder, Aerospace Engineer, Standardization Branch, ANM-113, FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (206) 227-1721; fax (206) 227-1149.

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 Saab Model SAAB SF340A and SAAB 340B series airplanes was published in the Federal Register on January 9, 1996 (61 FR 640). That action proposed to require visual and dye penetrant inspection(s) to detect cracks of the nose rib of the rudder, and stop drilling and blending of minor cracks. That action also proposed to require replacement of the nose rib with a new nose rib and reinforcement of the nose rib, if any extensive crack is detected or if an operator elects to terminate the repetitive inspections.

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 proposed rule.

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.

The FAA estimates that 221 Saab Model SAAB SF340A and SAAB 340B series airplanes of U.S. registry will be affected by this AD, that it will take approximately 4 work hours per airplane to accomplish the required actions, and that the average labor rate is $60 per work hour. Based on these figures, the cost impact of the inspection requirement of this AD on U.S. operators is estimated to be $53,040, or $240 per airplane.

The 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 theAmendment
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 USC 106(g), 40113, 44701.

39.13 - [Amended]
2. Section 39.13 is amended by adding the following new airworthiness directive: