AD 97-08-01

This amendment adopts a new airworthiness directive (AD), applicable to CFM International CFM56-3, -3B, -3C series turbofan engines, that requires a reduction of the low cycle fatigue (LCF) retirement lives for certain fan disks. This amendment is prompted by the results of a refined life analysis performed by the manufacturer which revealed minimum calculated LCF lives significantly lower than published LCF retirement lives. The actions specified by this AD are intended to prevent a LCF failure of the fan disk, which could result in an uncontained engine failure and damage to the aircraft.

Final rule.

97-08-01 CFM International: Amendment 39-9989. Docket 95-ANE-44.
Applicability: CFM International (CFMI) CFM56-3, -3B, and -3C series turbofan engines with fan disks, Part Number (P/N) 335-014-509-0 or 335-014-511-0, installed, that are currently operating at, or have previously operated at, the Category C thrust rating. These engines are installed on but not limited to Boeing 737 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 (g) of this AD. The request should include an assessment of the effect of the modification, alteration, or repairon 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 a low cycle fatigue (LCF) failure of the fan disk, which could result in an uncontained engine failure and damage to the aircraft, accomplish the following:
(a) For CFM56-3C series engines operating at the Category C thrust rating on the effective date of this AD, remove the fan disk prior to accumulating a total Category C thrust rating life of 20,100 cycles.
(b) For CFM56-3B and -3C series engines operating at the Category B thrust rating on the effective date of this AD, but which have previously operated at the Category C thrust rating, recalculate the fan disk total cycles remaining at the Category B thrust rating using a Category C thrust rating life of 20,100 cycles.
Note 2: The current fan disk Category B thrust ratinglife is 24,900 cycles, and is not affected by this AD.
(c) For CFM56-3, -3B, and -3C series engines operating at the Category A thrust rating on the effective date of this AD, but which have previously operated at the Category C thrust rating, recalculate the fan disk total cycles remaining at the Category A thrust rating using a Category C thrust rating life of 20, 100 cycles.
Note 3: The current fan disk Category A thrust rating life is 30,000 cycles, and is not affected by this AD.
(d) This action establishes the new Category C thrust rating LCF retirement life of 20,100 cycles listed in paragraphs (a), (b), and (c) of this AD. This retirement life is published in Chapter 05 of the CFM56-3 model series Engine Shop Manual, CFMI-TP.SM.5.
(e) The Category A, B, and C thrust ratings listed in paragraphs (a), (b), and (c) of this AD are defined in Chapter 05 of the CFM56-3 model series Engine Shop Manual, CFMI-TP.SM.5.
(f) The method to recalculate the retirement life, as stated in paragraphs (b) and (c) of this AD is defined in Chapter 05 of the CFM56-3 model series Engine Shop Manual, CFMI-TP.SM.5.
(g) 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. The request should be forwarded through an appropriate FAA Principal Maintenance Inspector, who may add comments and then send it to the Manager, Engine Certification Office.
Note 4: Information concerning the existence of approved alternative methods of compliance with this airworthiness directive, if any, may be obtained from the Engine Certification Office.
(h) 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.
(i) This amendment becomes effective on June 23, 1997.

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 CFM International (CFMI) CFM56-3C series turbofan engines was published in the Federal Register on October 10, 1995 (60 FR 52636). That action proposed to require a reduction of the low cycle fatigue (LCF) retirement lives for certain fan disks.
Interested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received.
Two commenters state that the proposed rule should be revised to address the LCF retirement lives for engines that may have operated at several thrust ratings, including the CFM56-3 and -3B engine models, since the retirement lives are dependent on the thrust rating. The FAA concurs. The FAA has revised the Applicability paragraph and paragraphs (a), (b), and (c) of this final rule accordingly.
Two commenters support the rule as proposed.
In addition, the FAA has added the specific fan disk part numbers to the Applicability paragraph of this AD in order to more accurately define the population of engines to which this AD applies.
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 described previously. 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 33 engines installed on aircraft of U.S. registry will be affected by this AD, and that it will not take any additional work hours per engine to accomplish the required actions. Assuming that the parts cost is proportional to the reduction of the LCF retirement lives, the required parts will cost approximately $17,275 per engine. Based on these figures, the total cost impact of the AD on U.S. operators is estimated to be $570,075.
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 USC 106(g), 40113, 44701. 39.13 - [AMENDED]
2. Section 39.13 is amended by adding the following new airworthiness directive: