# AGENCY:

 Federal Aviation Administration, DOT. 

# ACTION:

 Final rule. 

# SUMMARY:

 This amendment adopts a new airworthiness directive (AD), applicable to certain General Electric Company (GE) GE90 series turbofan engines, that requires reducing the cyclic life limits for certain fan mid shafts with undesirable microstructure, and removing from service those mid fan shafts prior to exceeding the new limits and replacing with serviceable parts. This amendment is prompted by reports of magnetic particle inspections conducted by the manufacturer identifying segregation in the raw material, resulting in lower fatigue life properties. The actions specified by this AD are intended to prevent fan mid shaft failure, which could result in a total loss of thrust and inflight engine shutdown. 

# DATES:

 Effective April 7, 2000. 

# FOR FURTHER INFORMATION CONTACT:

 William S. Ricci, Aerospace Engineer, Engine Certification Office, FAA, Engine and Propeller Directorate, 12 New England Executive Park, Burlington, MA 01803-5299; telephone 781-238-7742, fax 781-238-7199. 

# SUPPLEMENTARY INFORMATION:

                     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 not just 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, 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. 

## 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. 

Start Printed Page 5762
§ 39.13 

2. Section 39.13 is amended by adding the following new airworthiness directive: 

**2000-03-02 General Electric Company:**                         Amendment 39-11559. Docket 98-ANE-51-AD.                    

*Applicability:*                         General Electric Company (GE) GE90-90B, -85B, and -76B series turbofan engines, with fan mid shafts, part numbers (P/Ns) 1767M71G01, 1767M71G02, and 1767M75G02, installed. These engines are installed on but not limited to Boeing 777 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 (c) 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 fan mid shaft failure, which could result in a total loss of thrust and inflight engine shutdown, accomplish the following: 

## Reduced Life Limits 

(a) Remove from service fan mid shafts and replace with serviceable parts prior to the following new, lower cyclic life limits: 

(1) For fan mid shafts, P/N 1767M71G01, installed on GE90-85B and -90B series engines, the new life limit is 4,200 cycles-since-new (CSN). 

(2) For fan mid shafts, P/N 1767M71G02, installed on GE90-85B and -90B series engines, the new life limit is 4,200 CSN. 

(3) For fan mid shafts, P/N 1767M75G02, installed on GE90-76B, -85B, and -90B series engines, the new life limit is 8,200 CSN. 

(b) This AD establishes new life limits for fan mid shafts, P/N 1767M71G01, 1767M71G02, and 1767M75G02. Except as provided in paragraph (c) of this AD, no alternate life limits for these affected parts may be approved. 

## Alternative Methods of Compliance 

(c) 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.

(d) This amendment becomes effective on April 7, 2000.

Issued in Burlington, Massachusetts, on February 1, 2000.

David A. Downey,

Assistant Manager, Engine and Propeller Directorate, Aircraft Certification Service.

[FR Doc. 00-2686  Filed 2-4-00; 8:45 am]

BILLING CODE 4910-13-U