98-18-10: Low Pressure Turbine Disks

98-18-10 GENERAL ELECTRIC COMPANY: Amendment 39-10726. Docket 98-ANE-18-AD. Applicability: General Electric Company (GE) CF6-6 series turbofan engines, installed on but not limited to McDonnell Douglas DC-10-10 series aircraft. Note 1: This airworthiness directive (AD) applies to each engine 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 engines 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 low pressure turbine (LPT) stage 4 disk cracking, which could result in an uncontained engine failure and damage to the aircraft, accomplish the following: (a) Remove from service LPT stage 4 disks, part numbers (P/Ns) 9010M40P01, 9010M40P02, 9010M40P07, 9010M40P09, and 9010M40P12, and replace with serviceable parts, in accordance with the following schedule: (1) For disks with 12,300 or more cycles since new (CSN) but less than 24,000 CSN on the effective date of this AD, remove from service affected disks at the earliest of the following: (i) The next piece-part exposure after the effective date of this AD; or (ii) The next engine shop visit after accumulating 16,500 CSN; or (iii) Within 4,200 cycles in service (CIS) after the effective date of this AD; or (iv) Prior to exceeding 24,000 CSN. (2) For disks with 5,000 or more CSN, but less than 12,300 CSN, on the effective date of this AD, remove from service affected disks at the earlier of the following: (i) Prior to exceeding 16,500 CSN; or (ii) Within 7,300 CIS after the effective date of this AD. (3) For disks with less than 5,000 CSN on the effective date of this AD, remove from service affected disks prior to exceeding 12,300 CSN. (b) This AD establishes a new cyclic retirement life limit for LPT stage 4 disks of 12,300 CSN. Thereafter, except as provided in paragraph (d) of this AD, no alternative cyclic retirement life limits may be approved for LPT stage 4 disks. (c) For the purpose of this AD, the following definitions apply: (1) An engine shop visit is defined as separation of a major, static flange. (2) Piece-part exposure is when the affected part is completely disassembled in accordance with the disassembly instructions in the engine manual or section of the Instructions for Continued Airworthiness. (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, Engine Certification Office. Operators shall submit their requests through an appropriate FAA Principal Maintenance Inspector, who may add comments and then send it to the Manager, Engine Certification Office. Note 2: Information concerning the existence of approved alternative methods of compliance with this airworthiness directive, if any, may be obtained from the Engine Certification Office. (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 aircraft to a location where the requirements of this AD can be accomplished. (f) This amendment becomes effective on September 30, 1998.