AD 98-23-07 R1

Effective July 30, 1999.

Comments for inclusion in the Rules Docket must be received on or before September 28, 1999.

Submit comments in triplicate to the Federal Aviation Administration (FAA), New England Region, Office of the Regional Counsel, Attention: Rules Docket No. 98-ANE-21-AD, 12 New England Executive Park, Burlington, MA 01803-5299. Comments may also be sent via the Internet using the following address: ``9-ane-[email protected]''. Comments sent via the Internet must contain the docket number in the subject line.

Tara Goodman, Aerospace Engineer, Engine Certification Office, FAA, Engine and Propeller Directorate, 12 New England Executive Park, Burlington, MA 01803-5299; telephone (781) 238-7130, fax (781) 238-7199.

On November 5, 1998, the Federal Aviation Administration (FAA) issued Airworthiness Directive (AD) 98-23-07, amendment 39-10872 (63 FR 63393, November 13, 1998), applicable to certain Pratt & Whitney (PW) Models JT9D-7, -7A, -7H, -7AH, -7F, -7J, -20, -20J, -7Q, -7Q3, -59A, -70A, and -7R4D turbofan engines. That AD requires a one-time acid etch inspection of the turbine exhaust case (TEC) wall between and on either side of the ``R'' and ``S'' rails in the engine mount lug area (top quadrant of the case) for the presence of weld material, and if weld material is detected, removal from service and replacement with serviceable parts. That action was prompted by reports of weld rework performed in the outer case wall of the TEC, in the mount lug fillet area, during original production to address local under minimum wall thickness conditions which at the time was considered to have left the TEC's structural capability compromised. That condition, if not corrected, was considered to have the potential to result in TEC structural failure under abnormal operating conditions, which could result in reduced main mount load capability, engine separation from the wing and subsequent loss of control of the airplane.

Since the issuance of that AD, the FAA has reviewed detailed analyses for PW JT9D engine installations (excluding the JT9D-7R4 bulged low pressure turbine/TEC configurations). The analyses show that sufficient margin exists for TECs installed in JT9D-3A, -7, -7A, -7H, -7AH, -7F, -7J, -20, -20J, -7Q, -7Q3, -59A, -70A, and -7R4D engine configurations under abnormal operating conditions. The results also show that there are no flight safety issues resulting from weld rework in the outer case wall of the TEC in the mount lug fillet area.

Welding in the mount lug area of the TEC was performed on several PW JT9D series TECs during original manufacture in order to address case wall thickness that was below the minimum. Since original type certification and at present, cracking and welding are prohibited in the mount lug area in accordance with the Engine Manual, because of concern for structural integrity during abnormal operating conditions. The results of the analyses show that the area where welding is prohibited in the Engine Maintenance Manual can be redefined, such that welding would only be prohibited on the mount pads.

The FAA has reviewed the analytical results and has determined that welding in the fillets at the base of the ``R'' and ``S'' rails and the shell wall does not compromise the structural integrity of the TEC. Therefore, the FAA has determined that it is necessary to rescind AD 98-23-07 in order to prevent operators from performing an unnecessary action. The current AD requires a one-time inspection of the TEC to be performed at the next shop visit. Operators are currently facing the requirement to perform this unnecessary inspection; therefore, it is impractical to provide prior notice and opportunity for public comment before rescinding the current AD.

In addition, since this action rescinds a requirement to perform an unnecessary action, it has no adverse economic impact and imposes no additional burden on any person. Therefore, notice and public procedures hereon are impractical and the rescission may be made effective upon publication in the Federal Register.

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 on this rule by submitting such written data, views, or arguments as they may desire. Communications should 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 notice must submit a self-addressed, stamped postcard on which the following statement is made: ``Comments to Docket Number 98-ANE-21-AD.'' The postcard will be date stamped and returned to the commenter.

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:

1. The authority citation for part 39 continues to read as follows:

Authority: 49 U.S.C. 106(g), 40113, 44701.