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 General Electric Company (GE) GE90-90B, -85B, and -76B series turbofan engines was published in the Federal Register on November 26, 1999 (64 FR 66415). That action proposed to reduce the cyclic life limits for certain fan mid shafts with undesirable microstructure, and remove from service those fan mid shafts prior to exceeding the new limits and replace with serviceable parts. That action was prompted by reports of magnetic particle inspections conducted by the manufacturer identifying segregation in the raw material, resulting in lower fatigue life properties. That condition, if not corrected, could result in fan mid shaft failure, which could result in a total loss of thrust and inflight engine shutdown.
Comments Received
Interested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received.
Change Unsafe Condition Language
One commenter states that the statement of unsafe condition in the proposed rule is not accurate. The commenter believes that the language used does not correctly reflect the failure consequences of the fan mid shaft. The commenter also is concerned that the engine is not in compliance with Federal Aviation Regulations (FAR) 33 (14 CFR 33) requirements regarding shaft failure. The FAA concurs in part. Though the language used in the statement of unsafe condition in the proposal is typical of life limited parts ADs, a more accurate description of the failure consequences of the fan mid shaft would be a total loss of thrust and inflight engine shutdown. The statement of unsafe condition in this final rule has been changed accordingly.
GE90 Engine Model Applicability
The same commenter believes the proposal should apply to all GE90 engine models and notjust those listed in the applicability. The FAA does not concur. The proposal addresses those fan mid shaft part numbers (P/Ns) and engine models that have had their published life limits reduced. This proposal does not address the fan mid shafts P/Ns and engine models that have had their published life limits increased. These fan mid shafts P/Ns and engine model combinations are discussed in GE90 Alert Service Bulletin 72-A0389, Revision 1, dated August 25, 1999.
Delete Ferry Flight Authorization
The same commenter believes that the special flight permit authorization paragraph included in the proposal should be deleted. The commenter believes that ferry flight permits should not be authorized in the case of a life reduction AD. The FAA concurs and that paragraph has been removed from this final rule.
Concurrence
One commenter concurs with the rule as proposed.
Conclusion
After careful review of the available data, including the comments noted above, theFAA 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.
Economic Analysis
There are approximately 118 engines of the affected design in the worldwide fleet. The FAA estimates that 4 engines installed on aircraft of US registry will be affected by this AD and that the prorated life reduction will cost approximately $71,000 per engine. Based on these figures, the total cost impact of the AD on US operators is estimated to be $284,000.
Regulatory Impact
The regulations adopted herein will not have a substantial direct effect 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, it is determined that this final rule does not have federalism implications under Executive Order (EO) 13132.
For the reasons discussed above, I certify that this action (1) is not a "significant regulatory action" under EO 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, 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 U.S.C. 106(g), 40113, 44701. 39.13 [Amended]
2. Section 39.13 is amended by adding the following new airworthiness directive: