AD 99-04-07

This amendment adopts a new airworthiness directive (AD) that is applicable to certain Saab Model SAAB SF340A and SAAB 340B series airplanes. This action requires a review of the airplane maintenance records to identify the bottom engine vibration isolator, an inspection of the aft engine vibration isolator to determine whether the deflection is within limits, and various follow-on actions. 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 excessive engine vibration, which could lead to damage of the nacelle structure and result in reduced structural integrity and fire shielding capability of the nacelle structure, or which could lead to chafing of the fire sensor loop and a consequent nuisance fire warning and result in a precautionary engine shutdown.

Final rule; request for comments

99-04-07 SAAB AIRCRAFT AB: Amendment 39-11031. Docket 98-NM-373-AD.
Applicability: Model SAAB SF340A series airplanes, serial numbers 004 through 159 inclusive; and Model SAAB 340B series airplanes, serial numbers 160 through 453 inclusive; as specified in Saab Service Bulletin SAAB 340-71-057, Revision 02, January 26, 1999, including Attachment 1, dated January 20, 1999; 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 (h) 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 excessive engine vibration, which could result in damage of the nacelle structure and reduced structural integrity and fire shielding capability of the nacelle structure, or which could result in chafing of the fire sensor loop and a consequent nuisance fire warning and precautionary engine shutdown; accomplish the following:

(a) Within 400 flight hours after the effective date of this AD, review the airplane maintenance records to determine the serial number of the bottom engine vibration isolator assembly; in accordance with Saab Service Bulletin SAAB 340-71-057, Revision 02, dated January 26, 1999, including Attachment 1, dated January 20, 1999.

(1) If the serial number of the bottom engine vibration isolator assembly is listed in Attachment 1 of the service bulletin: Prior to further flight, accomplish the requirements of paragraph (b) of this AD.

(2) If the serial number of the bottom engine vibration isolator assembly is not listed in Attachment 1 of the service bulletin, and the assembly was received new from or overhauled by Barry Controls: No further action is required by this AD.

(3) If the serial number of the bottom engine vibration isolator assembly is not listed in Attachment 1 of the service bulletin, and was not received new from or overhauled by Barry Controls; or if the serial number cannot be identified: Prior to further flight, accomplish the requirements of paragraph (c) of this AD.

(b) For airplanes on which the serial number of the bottom engine vibration isolator is determined, during the review of the maintenance records required by paragraph (a) of this AD, to be listed in Attachment 1, dated January 20, 1999, of Saab Service Bulletin SAAB 340-71-057, Revision 02, dated January 26, 1999: Prior to further flight, remove the bottom engine vibration isolator and perform a one-time visual inspection of the area around the engine to detect chafing, in accordance with the service bulletin.

(1) If no chafing is detected, prior to further flight, install a new bottom engine vibration isolator having a molded assembly with a cure date other than 9801 through 9825 inclusive, and perform a visual inspection of the aft engine vibration isolator to determine whether the deflection is within allowable limits, in accordance with the service bulletin.

(i) If the deflection of the aft engine vibration isolator is within the limits specified in the service bulletin, no further action is required by this AD.

(ii) If the deflection of the aft engine vibration isolator is outside the limits specified in the service bulletin, prior to further flight, repair in accordance with a method approved by the Manager, International Branch, ANM-116, FAA, TransportAirplane Directorate; or the Luftfartsverket (LFV) (or its delegated agent).

(2) If any chafing is detected, prior to further flight, accomplish the requirements of paragraph (e) of this AD.
NOTE 2: Inspections and corrective actions accomplished prior to the effective date of this AD in accordance with Saab Service Bulletin SAAB 340-71-057, dated November 20, 1998; or Revision 01, dated December 18, 1998, including Attachment 1, dated December 11, 1998; are considered acceptable for compliance with the applicable actions specified in this amendment.

(c) For airplanes on which, during the review of the maintenance records required by paragraph (a) of this AD, the serial number of the bottom engine vibration isolator assembly is determined not to be listed in Attachment 1, dated January 20, 1999, of Saab Service Bulletin SAAB 340-71-057, Revision 02, dated January 26, 1999; and was not received new from or overhauled by Barry Controls; or cannot be identified: Prior to further flight, perform a visual inspection of the aft engine vibration isolator to determine whether the deflection is within allowable limits, and of the area around the engine to detect chafing; in accordance with Saab Service Bulletin SAAB 340-71-057, Revision 02, dated January 26, 1999, including Attachment 1, dated January 20, 1999; and accomplish the requirements of paragraph (c)(1), (c)(2), (c)(3), or (c)(4); as applicable.

(1) If the deflection of the aft engine vibration isolator is within the limits specified in the service bulletin, if no chafing of the area around the engine is detected, and if the bottom engine vibration isolator has accumulated 250 flight hours or more: No further action is required by this AD.

(2) If the deflection of the aft engine vibration isolator is within the limits specified in the service bulletin, if no chafing of the area around the engine is detected, and if the bottom engine vibration isolator has accumulated fewer than 250 flight hours: Repeat the inspection required by paragraph (b) of this AD one time within 250 flight hours after accomplishment of the first inspection required by paragraph (b) of this AD.

(3) If the deflection of the aft engine vibration isolator is outside the limits specified in the service bulletin, and if no chafing of the area around the engine is detected: Prior to further flight, accomplish the requirements of paragraph (d) of this AD.

(4) If any chafing of the area around the engine is detected: Prior to further flight, accomplish the requirements of paragraph (e) of this AD.

(d) For airplanes on which, during the inspection required by paragraph (c) of this AD, the deflection of the aft engine vibration isolator is determined to be outside the limits specified in Saab Service Bulletin SAAB 340-71-057, Revision 02, dated January 26, 1999, including Attachment 1, dated January 20, 1999; and no chafing of the area around the engine is detected: Prior to further flight, remove the aft engine vibration isolator, rotate the isolator 180 degrees, and perform a visual inspection of the snubbers to detect damage, in accordance with the service bulletin. Prior to further flight, repair any discrepant snubber or replace with a new or serviceable snubber, as applicable; reinstall the aft engine vibration isolator; and perform a visual inspection of the isolator to determine whether the deflection is within allowable limits; in accordance with the service bulletin.

(1) If the deflection of the aft engine vibration isolator is within the limits specified in the service bulletin and no chafing is detected, no further action is required by this AD.

(2) If the deflection of the aft engine vibration isolator is outside the limits specified in the service bulletin, prior to further flight, accomplish the requirements of paragraph (e) of this AD.

(e) For airplanes on which, during the inspection required by paragraph (b) or (c) of this AD, anychafing of the area around the engine was detected; or for airplanes on which, during the inspection required by paragraph (d)(2) of this AD, the deflection of the aft engine vibration isolator is determined to be outside the limits specified in Saab Service Bulletin SAAB 340-71-057, Revision 02, dated January 26, 1999, including Attachment 1, dated January 20, 1999: Prior to further flight, repair any chafing of the area around the engine, and replace any discrepant parts with new parts, and remove the bottom vibration isolator; in accordance with the service bulletin; and, prior to further flight, accomplish the requirements of paragraphs (e)(1), (e)(2), (e)(3), and (e)(4) of this AD.

(1) Perform a detailed visual inspection to detect cracked or broken parts of the bottom engine mount support fitting, and its adjacent structure and attaching hardware, in accordance with the service bulletin. Except as provided by paragraph (f) of this AD, prior to further flight, repair any cracked or broken part in accordance with the SAAB 340 Structural Repair Manual (SRM).

(2) Install a new bottom vibration isolator having a molded assembly with a cure date other than 9801 through 9825 inclusive, in accordance with the service bulletin.

(3) Perform a detailed visual inspection of the side and the aft engine vibration isolators for damage, in accordance with the service bulletin. If any damage is detected, prior to further flight, replace any damaged isolator with a new part, and perform a detailed visual inspection to detect cracked or broken parts of the affected engine mount support fitting and its adjacent structure and attaching hardware, in accordance with the service bulletin. Except as provided by paragraph (f) of this AD, if any damage of the fittings and adjacent structure is found, prior to further flight, repair in accordance with the SRM.

NOTE 3: Saab Service Bulletin SAAB 340-71-057, Revision 02, references Barry Controls Component Maintenance Manual Section 71-20-20, dated October 15, 1993, as an additional source of service information for accomplishment of the visual inspection of the side and aft engine vibration isolators.

(4) Perform a visual inspection of the aft engine vibration isolator to determine whether the deflection is within allowable limits, in accordance with the service bulletin.

(i) If the deflection of the aft engine vibration isolator is within the limits specified in the service bulletin, no further action is required by this AD.

(ii) If the deflection of the aft engine vibration isolator is outside the limits specified in the service bulletin, accomplish the requirements of paragraph (f) of this AD.

(f) If, during the inspections required by paragraph (e)(1) or (e)(3) of this AD, any damage is found that is outside the limits specified by the SRM; or if, during the inspection of the aft engine vibration isolator required by paragraph (e)(4) of this AD, the deflection isoutside the limits specified in the service bulletin: Prior to further flight, repair in accordance with a method approved by the Manager, International Branch, ANM-116, FAA, or the LFV (or its delegated agent).

(g) As of the effective date of this AD, no person shall install on any airplane a bottom vibration isolator molded assembly having P/N 00-13226-03 and a cure date 9801 through 9825 inclusive.

(h) 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 4: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the International Branch, ANM-116.

(i) Special flight permitsmay 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.

(j) Except for the repair actions as provided by paragraphs (b)(1)(ii), (e)(1), (e)(3), and (f) of this AD, the actions shall be done in accordance with Saab Service Bulletin SAAB 340-71-057, Revision 02, dated January 26, 1999, including Attachment 1, dated January 20, 1999, which contains the following list of effective pages:

Page Number
Revision Level
Shown on Page
Date
Shown on Page
1-5
02
January 26, 1999

Attachment 1
1-10
None
January 20, 1999

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, Linkoping, 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.

NOTE 5: The subject of this AD is addressed in Swedish airworthiness directive SAD 1-135R1, dated December 18, 1998.

(k) This amendment becomes effective on February 25, 1999.

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.

The Luftfartsverket (LFV), which is the airworthiness authority for Sweden, notified the FAA that an unsafe condition may exist on certain Saab Model SAAB SF340A and SAAB 340B series airplanes. The LFV advises that degraded bottom engine mounts have been found on several airplanes. Investigation has revealed that the isolator material used in the manufacture of certain bottom engine mounts degrades after a short time in service. Such degradation of the isolator material changes the damping characteristics of the engine support system and results in excessive engine vibration. Such excessive engine vibration could lead to damage of the nacelle structure, and consequent reduced structural integrity and fire shielding capability of the nacelle.

The LFV also advises that it has received a report of chafing of the fire sensor loop on several airplanes. Such chafing also has been attributed to excessive engine vibration and could result in a nuisance fire warning and a precautionary engine shutdown. Precautionary engine shutdown could compromise the safe takeoff of the airplane.

In addition, the LFV advises that it has received a report indicating that the air pressure tube of the engine nacelle was found damaged on several airplanes. That damage also has been attributed to excessive engine vibration. Damage to the air pressure tube could cause loss of cooling to the power turbine discs of the engine, which could result in failure of the blades of the power turbine disc, and consequent uncontained failure of the engine.

Explanation of Relevant Service Information
Saab has issued Service Bulletin SAAB 340-71-057, Revision 02, dated January 26, 1999, including Attachment 1, dated January 20, 1999. The service bulletin describes procedures for a review of the airplane maintenance records to identify the bottom engine vibration isolator, a visual inspection of the aft engine vibration isolator to determine whether the deflection is within limits, and various follow-on actions. The follow-on actions, as applicable, include one repetition of the visual inspection of the aft engine vibration isolator to determine whether the deflection is within limits; a one-time visual inspection to detect chafing of the area around the engine; replacement of the existing bottom engine vibration isolator with a new part; repair or replacement of discrepant parts; visual inspections to detect damage of the side and aft engine vibration isolators, and replacement, if necessary; and detailed visual inspections to detect cracked or broken parts of the engine mount support fitting, adjacent structure, and attaching hardware of the bottom, side, and aft engine mount support fittings.

The Saab service bulletin references Barry Controls Service Letter 939-71-02, dated January 20, 1999, as the appropriate source of criteria for the inspection of the bottom vibration isolator. The Saab service bulletin includes that service letter as Attachment 1.

The Saab service bulletin references Barry Controls Component Maintenance Manual Section 71-20-20, dated October 15, 1993, as an additional source of service information to accomplish the visual inspection of the side and aft engine vibration isolators.

Accomplishment of the actions specified in the Saab service bulletin is intended to adequately address the identified unsafe condition. The LFV classified Saab Service Bulletin SAAB 340-71-057, Revision 1, dated December 18, 1998 (including Attachment 1, dated December 11, 1998), as mandatory and issued Swedish airworthiness directive SAD 1-135R1, dated December 18, 1998, in order to assure the continued airworthiness of these airplanes in Sweden.

FAA's Conclusions
These airplane models are manufactured in Sweden and are 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 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 is being issued to prevent excessive engine vibration, which could lead to damage of the nacelle structure and result in reduced structural integrity and fire shielding capability of the nacelle structure, or which could lead to chafing of the fire sensor loop and a consequent nuisance fire warning and result in a precautionary engine shutdown. This AD requires accomplishment of the actions specified in the Saab service bulletin described previously, except as discussed below.

Differences Between This Rule and the Service Bulletin
Operators should note that, although the service bulletin describes procedures for a detailed visual inspection of the bottom engine vibration isolator if any chafing of the area around the engine is detected, this AD requires replacement of the bottom engine vibration isolator with a new part if any such chafing is found. The FAA has determined that a detailed visual inspection may not provide the degree of safety assurance necessary for the transport airplane fleet. The FAA finds that continued safety of the transport airplane fleet will be better assured by elimination of the source of the problem (i.e., by replacing the bottom engine vibration isolator), rather than by an inspection. The replacement requirement is in consonance with these conditions.

Operators also should note that, although the service bulletin specifies detailed visual inspections of the affected engine mount support fitting, adjacent structure, and attaching hardware if any engine vibration isolator is replaced; the service bulletin does not specify any source of service information for corrective actions if any discrepancies are found during such inspections. This AD requires any cracked or broken part of the engine mount support fitting, adjacent structure, and attaching hardware of the bottom, side, and aft engine mount support fittings to be repaired prior to further flight in accordance with the SAAB 340 Structural Repair Manual.

Operators also should note that the service bulletin specifies, for airplanes on which no chafing is detected during the inspection of the area around the engine, a visual inspection of the aft engine vibration isolator to determine whether the deflection is within allowable limits following replacement of the bottom vibration isolator. However, the service bulletin does not specify what actions should be accomplished if, during such inspection, the deflection is determined to be outside the limits specified in the service bulletin. This AD requires repair prior to further flight in accordance with a method approved by the FAA or the LFV (or its delegated agent), for airplanes on which no chafing is detected, but on which the deflection of the aft engine vibration isolator is determined to be outside the limits specified in the service bulletin.

Determination of Rule's Effective Date
Since a situation exists that requires the immediate adoption of this regulation, it is found that notice and opportunity for prior public comment hereon are impracticable, and that good cause exists for making this amendment effective in less than 30 days. Comments Invited

Although this action is in the form of a final rule that involves requirements affecting flight safety and, thus, was not preceded by notice and an opportunity for public comment, comments are invited on this rule. Interested persons are invited to comment onthis 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 98-NM-373-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.

The FAA has determined that this regulation is an emergency regulation that must be issued immediately to correct an unsafe condition in aircraft, and that it is not a "significant regulatory action" under Executive Order 12866. It has been determined further that this action involves an emergency regulation under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979). If it is determined that this emergency regulation otherwise would be significant under DOT Regulatory Policies and Procedures, a final regulatory evaluation will be prepared and placed in the Rules Docket. A copy of it, if filed, 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: 2.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: