Airworthiness Directives; General Electric Company CF6-45 and CF6-50 Series Turbofan Engines

AGENCY:

Federal Aviation Administration (FAA), Department of Transportation (DOT).

ACTION:

Supplemental notice of proposed rulemaking (NPRM); reopening of comment period.

SUMMARY:

This supplemental NPRM revises an earlier proposed airworthiness directive (AD), applicable to certain General Electric Company (GE) CF6-45 and CF6-50 series turbofan engines. That proposed AD would have required inspecting and reworking certain forward and aft centerbodies of the long fixed core exhaust nozzle (LFCEN) assembly. That proposed AD resulted from reports of separation of the forward and aft centerbodies of the LFCEN assembly due to high-imbalance engine conditions. This supplemental NPRM revises the proposed AD to add one engine model, and by replacing the LFCEN instead of repairing the centerbodies. This proposed AD results from the engine manufacturer issuing new service information. We are proposing this AD to prevent the forward and aft centerbody of the LFCEN assembly from separating, leading to additional damage to the airplane.

DATES:

We must receive any comments on this proposed AD by February 19, 2008.

ADDRESSES:

Use one of the following addresses to comment on this proposed AD.

• Federal eRulemaking Portal: Go to http://www.regulations.gov and follow the instructions for sending your comments electronically.
• Mail: Docket Management Facility, U.S. Department of Transportation, 1200 New Jersey Avenue, SE., West Building Ground Floor, Room W12-140, Washington, DC 20590-0001.
• Hand Delivery: Deliver to Mail address above between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays.
• Fax: (202) 493-2251.

You can get the service information identified in this proposed AD from General Electric Company via GE-Aviation, Attn: Distributions, 111 Merchant St., Room 230, Cincinnati, Ohio 45246, telephone (513) 552-3272; fax (513) 552-3329.

FOR FURTHER INFORMATION CONTACT:

Robert Green, Aerospace Engineer, Engine Certification Office, FAA, Engine & Propeller Directorate, 12 New England Executive Park, Burlington, MA 01803; e-mail: robert.green@faa.gov; telephone (781) 238-7754; fax (781) 238-7199.

SUPPLEMENTARY INFORMATION:

Comments Invited

We invite you to send us any written relevant data, views, or arguments regarding this proposal. Send your comments to an address listed under ADDRESSES. Include “Docket No. FAA-2006-24145; Directorate Identifier 2006-NE-06-AD” in the subject line of your comments. We specifically invite comments on the overall regulatory, economic, environmental, and energy aspects of the proposed AD. We will consider all comments received by the closing date and may amend the proposed AD in light of those comments.

We will post all comments we receive, without change, to http://www.regulations.gov , including any personal information you provide. We will also post a report summarizing each substantive verbal contact with FAA personnel concerning this proposed AD. Using the search function of the Web site, anyone can find and read the comments in any of our dockets, including, if provided, the name of the individual who sent the comment (or signed the comment on behalf of an association, business, labor union, etc.). You may review the DOT's complete Privacy Act Statement in the Federal Register published on April 11, 2000 (65 FR 19477-78).

Examining the AD Docket

You may examine the AD docket on the Internet at http://www.regulations.gov ; or in person at the Docket Operations office between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. The AD docket contains this proposed AD, the regulatory evaluation, any comments received, and other information. The street address for the Docket Operations office (telephone (800) 647-5527) is the same as the Mail address provided in the ADDRESSES section. Comments will be available in the AD docket shortly after receipt.

Discussion

On March 27, 2006, we issued a proposal to amend part 39 of the Code of Federal Regulations (14 CFR part 39) to add an AD, applicable to GE CF6-45 and -50 series turbofan engines. The proposed AD published as an NPRM in the Federal Register on March 31, 2006 (71 FR 16246). That NPRM proposed to require reworking the forward and aft centerbodies to add doublers, larger nuts and bolts, and higher strength corrosion resistant nut plates. That rework would be required the next time the forward centerbody and aft centerbody are removed from the engine after the effective date of this proposed AD.

Since we issued that NPRM, we determined that the referenced GE rework instructions in GE service bulletin (SB) No. CF6-50 S/B 78-0242 were incompatible with the existing repair in the Engine Manual. GE subsequently superseded SB No. CF6-50 S/B 78-0242 with SB No. GE CF6-50 S/B 78-0244, which corrected the error. We also found that we didn't specify the CF6-50A model engine in the Applicability of the proposed AD. We added the CF6-50A engine model to the Applicability of the proposed AD. Because we expanded the population of affected engines by adding the CF6-50A model, this supplemental NPRM reopens the comment period to include the CF6-50A engine model and references the new rework instructions.

This condition, if not corrected, could result in the forward and aft centerbody of the LFCEN assembly separating, leading to additional damage to the airplane.

Comments

We provided the public the opportunity to participate in the development of this proposed AD. We have considered the comments received.

Request for Continued Operational Serviceability Limits

One commenter asks us to provide continued-operation serviceability limits in terms of flight cycles or flight hours and a maximum allowable crack length to allow operators to schedule removing and installing the LFCEN if a crack is found during an in-service, line station inspection. The commenter states that specifying continued-operation serviceability limits will preclude unscheduled maintenance and costly downtime. We don't agree that we should provide continued-operation serviceability limits in this proposed AD. An operator's approved maintenance plan should define the continued-operation serviceability criteria. We didn't change the proposed NPRM.

Request To Remove Requirement To Modify LFCEN to SB CF6-50 S/B 78-0242

Atlas Air asks us to remove the requirement to use GE SB No. CF6-50 S/B 78-0242 to modify the LFCEN. Atlas Air believes that they can maintain an equivalent level of safety by modifying the forward and aft centerbody as specified in GE SB No. CF6-50 S/B 78-0216, Revision 1, dated October 23, 1987, and adhering to the torque requirements for the aft centerbody bolts as specified in GE SB No. CF6-50 S/B 78-0241, dated January 7, 2003. Atlas Air notes that after the OEM introduced SB No. CF6-50 S/B 78-0216 Revision 1, which instituted the Sixteen-bolt Forward and Aft Centerbody Configuration, 22 events were recorded. But, the OEM has not provided data as to how many of the 22 events occurred on centerbodies modified using only SB No. CF6-50 S/B 78-0216, Revision 1. Atlas Air also notes that no events of separations of the forward and aft centerbody have occurred since the OEM introduced the increased torque requirements for the forward-to-aft centerbody joint bolts.

We don't agree. Analysis and component tests following release of GE SB No. CF6-50 S/B 78-0216 and SB No. CF6-50 S/B 78-0241 identified several other design shortcomings at fan blade-out imbalance loads. Improvements released through GE SB No. CF6-50 S/B 78-0242 (and subsequently GE SB No. CF6-50 S/B 78-0244) addressed those design concerns. GE SB No. CF6-50 S/B 78-0216 and SB No. CF6-50 S/B 78-0241 don't address fully the identified LFCEN forward-to-aft centerbody separation issues. Incorporating the modifications defined in GE SB No. CF6-50 S/B 78-0244 would preclude the need to require repetitive on-wing inspections. We didn't change the proposed NPRM.

Request To Change the Compliance Time

Atlas Air proposes that we change the compliance time for modifying the forward and aft centerbody as specified in GE SB No. CF6-50 S/B 78-0242 from “the next time the forward and aft centerbody is removed from the engine” to “each time the forward or aft centerbody is removed and routed for repair.” Atlas Air states that the requirement to modify the forward and aft centerbody each time they remove an engine will increase the number of spare centerbodies needed. Atlas Air calculates the need for an additional five forward and aft centerbodies at an additional cost of $696,960.

We don't agree. Incorporating the GE SB No. CF6-50 S/B 78-0244 modifications when the centerbodies are repaired for unserviceable conditions would extend the compliance period unreasonably. The intent of the original compliance recommendation was to align and execute the modifications with engine refurbishments. The intent of the hard-time compliance period recommendation in this superseding NPRM is to complete the modifications within the same time period as the original engine removal recommendations. We didn't change the proposed NPRM.

Request To Change the Costs of Compliance

Atlas Air also believes that we underestimated the cost impact of the proposed rule. Atlas Air uses third party labor and does not agree that the $80 per hour rate is the true industry average. Atlas Air also observes that we do include the cost of spare centerbodies that would be required to support the compliance requirements of this rule. Atlas Air used a figure of $100 per hour in their subsequent cost calculation and included required spare parts in their projected compliance costs.

We don't agree. We use the average labor rate established by the Office of Aviation Policy, Plans, and Management Analysis (APO) for estimating the projected cost impact of ADs. We don't project additional costs associated with spare parts, because ADs address an unsafe condition in a product (in this case an engine) and the unsafe condition doesn't exist until the spare parts are on the engine and the engine is in service.

However, GE made corrections to SB No. CF6-50 S/B 78-0244, dated July 30, 2007, that included a revision of the projected labor work-hours to complete the modification. GE SB No. CF6-50 S/B 78-0242, dated September 26, 2005, cited 22 work-hours to complete the modification. That was for one centerbody half. The total labor work-hours to modify both centerbodies are 44 work-hours, which is cited in GE SB No. CF6-50 S/B 78-0244, dated July 30, 2007. We changed the Costs of Compliance section in the AD to reflect 44 work-hours per product.

Request To Change the Compliance Times

One commenter, FedEx, suggests a hard-time limit of 30 months after the effective date of the proposed AD to modify all LFCEN assemblies in accordance with GE SB No. CF6-50 S/B 78-0242 (subsequently superseded by GE SB No. CF6-50 S/B 78-0244) instead of when the centerbodies are removed when an engine is taken off wing. FedEx believes that the requirement to perform the modification at the next engine change will create an undue burden on line maintenance operations and prolong completing the modifications. Spare engines ship without the LFCEN assembly which is typically transferred to the new engine from the old engine at engine replacement. FedEx states that, under the requirements in the current NPRM, operators will have to pre-position spare LFCEN assemblies with spare engines to remote outstations. This requirement and additional logistics will unduly increase operator spare cost and cost of out of service aircraft. FedEx contends that a hard-time compliance limit will relieve operations from the increased logistics and spare costs and accelerate completion of the modification. With the current requirement to complete the modification when the LFCEN is removed from the engine, accomplishment could take more than 4 years. A fixed time of 30 months, versus at next engine removal, would allow operators to control the modifications at heavy maintenance checks and expedite completion of the modifications directed by this proposed AD.

We partially agree. We agree that a hard-time completion recommendation works better than an engine removal basis for the centerbody rework. We don't agree that 30 months is the appropriated compliance period. We revised the proposed NPRM accordingly, citing a 42 month compliance period. The 42 month limit is based on the CF6-50 average time-on-wing performance and annual utilization.

Request for a Grace Period

Two commenters, the Air Transport Association and Northwest Airlines, request a grace period of 12 months after the effective date of the proposed AD to acquire and modify spare forward and aft centerbodies. The commenters state that the available number of modified spare centerbody assemblies is extremely low and the grace period for provisioning would avoid extended aircraft-on-ground situations. We don't agree that a grace period is necessary, given our response to the previous comment. We didn't change the proposed NPRM.

Differences Between the Service Bulletin and the Component Maintenance Manual Repair Procedure

Two commenters identified issues with incorporating GE SB No. CF6-50 S/B 78-0242, dated September 26, 2005.

One commenter, Air Nippon Airways, requests that the GE SB recommend the CMM 78-11-02 repair modification for the forward centerbodies and that they be reflected in the FAA AD. Air Nippon Airways notes that the fastener locations on the forward centerbody aft doubler and aft doubler splices defined by GE SB No. CF6-50 S/B 78-0242 and GE Repair Document (RD) 250-206-S1 are different than those defined by the corresponding Component Maintenance Manual (CMM) repair. The aft doubler and aft doubler splices could not be installed on forward centerbodies that had been repaired in accordance with the CMM 78-11-02 Repair 001. In addition, the band doubler specified by the GE SB was already required with the CMM repair. We agree. ANA is correct in their statement that the GE SB No. CF6-50 S/B 78-0242, dated September 26, 2005, and CMM instructions were incompatible. GE subsequently superseded SB No. CF6-50 S/B 78-0242, dated September 26, 2005, with GE SB No. CF6-50 S/B 78-0244, dated July 30, 2007, which corrects the error by referencing the pre-existing repair for modifying the forward centerbody. We changed the proposed NPRM references to reflect the corrected service bulletin instructions.

One commenter, Airbus, reports that since release of the NPRM, docket No. FAA-2007-24145 (Directorate identifier 2006-NE-06-AD), operators report having difficulties implementing GE SB No. CF6-50 S/B 78-0242, dated September 26, 2005, due to a parallel spot-weld repair in Engine Manual Repair 78-11-02-300-001. That repair incorporates an aft joint doubler that interferes with the repair required by GE SB No. CF6-50 S/B 78-0242, dated September 26, 2005. Airbus notes that GE was revising SB No. CF6-50 S/B 78-0242, dated September 26, 2005, to define the proper doublers, update the repair, and contact the service bulletin. Airbus asks if we were informed of this situation and whether it is planned to postpone or review the current proposed rulemaking.

We were aware of the identified issues with the original service bulletin recommendations and that GE was revising SB No. CF6-50 S/B 78-0242, dated September 26, 2005. This proposed AD references the revised modifications released by GE SB No. CF6-50 S/B 78-0244, dated July 30, 2007. This proposed AD addresses those accomplishment instruction changes, and address the compliance recommendations proposed by FedEx, the ATA, and Northwest Airlines. We didn't change the proposed NPRM.

Relevant Service Information

We have reviewed and approved the technical contents of GE SB No. CF6-50 S/B 78-0244, dated July 30, 2007, that identifies disassembly, inspection, rework, and reassembly procedures for the forward and aft centerbodies.

Differences Between the Proposed AD and the Service Information

GE SB No. CF6-50 S/B 78-0244, dated July 30, 2007 requires reworking the forward and aft centerbodies when the centerbodies are removed from the engine. This proposed NPRM requires replacing the centerbodies with centerbodies that were modified using the Accomplishment Instructions, Section 3, of GE SB No. CF6-50 S/B 78-0244, dated July 30, 2007, within 42 months of the effective date of the proposed AD.

FAA's Determination and Requirements of the Proposed AD

We evaluated all pertinent information and identified an unsafe condition that is likely to exist or develop on other products of this same type design. We are proposing this AD, which will require replacing certain forward and aft centerbodies with new or modified forward and aft centerbodies. These replacements are required within 42 months after the effective date of this proposed AD. The proposed AD would require you to use the service information described previously to modify the forward and aft centerbodies before assembling them to the engine.

Costs of Compliance

We estimate that this proposed AD would affect 379 GE CF6-45 and CF6-50 series turbofan engines installed on airplanes of U.S. registry. We also estimate that it would take about 44 work hours per engine to perform the proposed actions, and that the average labor rate is $80 per work hour. Required parts would cost about $11,000 per engine. Based on these figures, we estimate the total cost of the proposed AD to U.S. operators to be $2,802,360.

Authority for This Rulemaking

Title 49 of the United States Code specifies the FAA's authority to issue rules on aviation safety. Subtitle I, Section 106, describes the authority of the FAA Administrator. Subtitle VII, Aviation Programs, describes in more detail the scope of the Agency's authority.

We are issuing this rulemaking under the authority described in Subtitle VII, Part A, Subpart III, Section 44701, “General requirements.” Under that section, Congress charges the FAA with promoting safe flight of civil aircraft in air commerce by prescribing regulations for practices, methods, and procedures the Administrator finds necessary for safety in air commerce. This regulation is within the scope of that authority because it addresses an unsafe condition that is likely to exist or develop on products identified in this rulemaking action.

Regulatory Findings

We have determined that this proposed AD would not have federalism implications under Executive Order 13132. This proposed AD would 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.

For the reasons discussed above, I certify that the proposed regulation:

1. Is not a “significant regulatory action” under Executive Order 12866;

2. Is not a “significant rule” under the DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and

3. Would not have a significant economic impact, positive or negative, on a substantial number of small entities under the criteria of the Regulatory Flexibility Act.

We prepared a regulatory evaluation of the estimated costs to comply with this proposed AD. See the ADDRESSES section for a location to examine the regulatory evaluation.

List of Subjects in 14 CFR Part 39

• Air transportation
• Aircraft
• Aviation safety
• Safety

The Proposed Amendment

Under the authority delegated to me by the Administrator, the Federal Aviation Administration proposes to amend 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.