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Airworthiness Directives; Pratt & Whitney PW4000 Series Turbofan Engines

Document Details

Information about this document as published in the Federal Register.

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AGENCY:

Federal Aviation Administration, DOT.

ACTION:

Final rule.

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SUMMARY:

This amendment adopts a new airworthiness directive (AD), that is applicable to certain models of Pratt & Whitney PW4000 series turbofan engines. This amendment requires operators to perform initial and repetitive inspections for cracking of high pressure compressor (HPC) front drum rotors based on cycle usage. This amendment also requires the removal from service of any cracked HPC front drum rotors. This amendment is prompted by reports that 11 HPC drum rotors have been found cracked on the spacer surface between the sixth and seventh stage disks. The actions specified by this AD are intended to detect premature cracking of the HPC drum rotor that could result in an uncontained engine failure and damage to the airplane.

DATES:

Effective date November 16, 2001. The incorporation by reference of certain publications listed in the regulations is approved by the Director of the Federal Register as of November 16, 2001.

ADDRESSES:

The service information referenced in this AD may be obtained from Pratt & Whitney, 400 Main Street, East Hartford, CT 06108. This information may be examined at the FAA, New England Region, Office of the Regional Counsel, 12 New England Executive Park, Burlington, MA; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC.

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FOR FURTHER INFORMATION CONTACT:

Tara Goodman, Aerospace Engineer, Engine Certification Office, FAA, Engine and Propeller Directorate, 12 New England Executive Park, Burlington MA 01803-5299; telephone: 781-238-7130, fax: 781-238-7199.

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SUPPLEMENTARY INFORMATION:

A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) to include an AD that is applicable to certain models of Pratt & Whitney (PW) PW4000 series turbofan engines was published in the Federal Register on March 22, 2001 (66 FR 16017). That action proposed to require operators to perform initial and repetitive inspections for cracking of high pressure compressor (HPC) front drum rotors based on cycle usage. The action also proposed to require the removal from service of any cracked HPC front drum rotors in accordance with PW Alert Service Bulletin (ASB) No. PW4ENG A72-722, dated September 29, 2000.

Comments

Interested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received.

Five-Cycle Flyback Allowance

Six commenters express concern with the deletion of the five-cycle flyback allowance.

One commenter requests clarification of the difference between the NPRM and ASB 72-722 with respect to the deletion of the five-cycle flyback allowance for engines with indications requiring eddy current inspection (ECI) verification.

Another commenter states that the AD should provide the five-cycle flyback allowance because eight reported findings of HPC front drum cracking were discovered in the shop and that the cracks do not propagate quickly.

A third commenter expresses concern that in cases of suspect cracks, the airline would incur an undue economic burden waiting for confirmation as to whether the visual indication is a crack or not. Also, the commenter suggests an initial inspection threshold of 1,200 cycles-since-new and a 20-cycle window for ECI reinspection to verify a visual crack indication. The commenter suggests that it is preferable to inspect compressor drums at a more frequent inspection interval and allow an engine with a “suspect” crack to continue in service for a limited time to allow for planning a reinspection. The same commenter suggests a 1,500 cycle repetitive inspection.

Another commenter provided information on the nature of the crack findings to date. Fifteen engines were identified with crack indications through borescope inspection. Three were obvious visual cracks and 12 required further assessment using the ECI inspection procedure cited in the SB. These 12 indications were confirmed not to be cracks.

Two commenters state that the five-cycle allowance for additional nondestructive inspections is effective in eliminating false initial crack indications and should be reinstated.

The FAA agrees that the five-cycle flyback allowance for engines with suspect crack indications is acceptable. Since the publication of the NPRM, results of a metallurgical investigation were provided that substantiate the five-cycle flight allowance. This information also determined that if a suspect crack indication extends from the knife edges to the disk radius of the sixth or seventh stage, an ECI reinspection must be accomplished before further flight. Accordingly, a five-cycle flyback allowance has been added to the compliance section of the AD.

However, the FAA does not agree with the suggested 20-cycle reinspection window or with the 1,500 cycle repetitive inspection interval. The FAA based the initial inspection threshold, reinspect flight allowance, and repetitive inspection interval on a risk assessment that uses known inspection data results to date.

Initial Front Drum Rotor Inspection

Several commenters request clarification regarding initial and repetitive inspection of the HPC front drum rotors. Two commenters request clarification of the requirement stated in the NPRM that the initial inspection be performed before the drum accumulates 1,500 cycles-since-new (CSN). Other commenters express concern that the NPRM does not address front drum rotors that exceed 1,500 CSN.

The FAA agrees. It is the FAA's intent to be consistent with the analytical data associated with HPC front drum rotor cracking. The ASB states that the initial borescope inspection should be performed on all HPC front drum rotors that have accumulated 1,000 cycles (total drum cycles), at the next “A” check, or 500 cycles after the receipt of the ASB. The FAA agrees with the inspection threshold of 500 cycles determined by the risk assessment and chose the upper limit of 1,500 CSN as the compliance threshold for the initial inspection. Rewording the initial inspection threshold inadvertently introduced confusion. The requirements of the ASB and the AD are equivalent because they are based on the same data. Therefore, the FAA will change the wording to be consistent with the ASB.

Repetitive Front Drum Rotor Inspection

One commenter requests that a drum rotor that was inspected in accordance with SB 72-722, having a total time beyond 1,500 CSN when inspected, be permitted to remain in service.

Another commenter asks if the AD has the same exemption as the ASB, which states that HPC front drum rotors previously inspected in accordance with the CIR Manual requirement at the last shop visit within 500 cycles, are exempt from the initial borescope inspection. That commenter also states that the requirement is not clear for the repetitive inspection requirement for HPC front drum rotors that were previously inspected in the shop.

Another commenter states that the provision in ASB PW4ENG A72-722 that exempts drums that were detail-part-inspected within 500 cycles from the initial inspection and fall into the 2,200 cycle reinspection interval should be included in the final rule. Start Printed Page 52025

The FAA agrees that if an HPC front drum rotor was inspected in accordance with On-Wing paragraphs of ASB 72-722, as required by the proposed rule, the initial inspection requirement is satisfied. However, the rotor is still subject to the repetitive On-Wing inspection requirements, within 2,200 cycles since last inspection.

The FAA also agrees that an HPC front drum rotor inspected in the shop utilizing the flourescent penetrant inspection (FPI) procedure within the past 500 CIS is exempt from the initial borescope inspection. Again, the rotor is still subject to the repetitive On-Wing inspection requirements, within 2,200 cycles since last inspection.

Omission of ECI

One commenter requests that the ECI of ASB 72-722 be omitted when the drum rotor is FPI per SPOP82 (CIR P/N 51A357 72-35-00). Another commenter asks whether the HPC front drum knife edge spacer area between the sixth and seventh stage disks previously visually inspected with split case condition or during light maintenance also should be exempted from initial borescope inspection.

As noted above, the FAA agrees that an HPC front drum rotor that was fluorescent penetrant inspected in the shop, as cited in the compliance section of the ASB, within the past 500 cycles in service (CIS), satisfies the initial inspection requirement. The ECI inspection requirement that is provided to confirm a suspect crack indication does not apply to HPC front drum rotors that have been fluorescent penetrant inspected in the shop within the past 500 CIS. The in-shop FPI inspection is more rigorous than the on-wing inspection requirements.

Number of Confirmed Cracked Drum Rotors

One commenter provides new information that there are eleven confirmed cracked HPC front drum rotors to date as compared to the seven that were described in the Summary and Discussion Sections of the NPRM. The FAA agrees that the higher number is accurate.

Raise Inspection Requirement

One commenter expresses a preference to inspect after 3,000 CIS, given that operator's experience with HPC front drum rotor cracking.

The FAA does not agree with the suggested 3,000 cycle repetitive inspection interval. The FAA based the initial inspection threshold, reinspect flight allowance, and repetitive inspection interval on a 20-year cumulative risk assessment that uses known inspection data results to date. The AD provides for individual operators to submit substantiating data that would support an increase in the repetitive inspection interval under the alternative method of compliance paragraph.

Inclusion of PW SB PW4ENG A72-693 in AD

One commenter states that the inspection procedure in Pratt & Whitney Service Bulletin PW4ENG A72-693 is the same as that required by the proposed rule; therefore, “credit” should be given for the inspections previously performed using this SB.

The FAA disagrees. PW ASB PW4ENG A72-693 was not referenced in the NPRM because that was a fleetwide campaign that has been completed and was not part of the 20-year risk assessment for which the start date was June 2000. However, credit will be given for inspections done prior to the issuance of this AD depending on when and how they were accomplished. These should be evaluated on an individual case basis within the context of the alternative method of compliance provision of the AD.

Exemption of PW4158 Engine Serial Numbers

One commenter notes that Revision 1 of the ASB does not exempt PW4158 engine serial numbers P728534 through P728546 from the inspection requirements and the AD does not need to include this information in the description of the differences between the manufacturer's service information and this AD. The FAA agrees and that statement has been removed from the AD.

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.

Differences Between Manufacturer's Service Information and This AD

Since the publication of the NPRM, the manufacturer revised, and the FAA has approved the technical contents of alert service bulletin (ASB) No. PW4ENG A72-722, Revision 1, dated June 7, 2001. Although ASB No. PW4ENG A72-722, Revision 1, dated June 7, 2001, provides procedures for operators to perform off-wing initial and repetitive HPC drum rotor inspections, the off-wing requirements are not mandated by this AD. The FAA has evaluated a 20-year cumulative risk assessment and has determined that an acceptable level of safety will be met by requiring the on-wing inspections at the cyclic intervals detailed in the ASB.

Economic Analysis

The FAA estimates that there are 1,970 engines of the affected design in the worldwide fleet, and that 538 engines installed on aircraft of U.S. registry would be affected by this proposed AD. The FAA also estimates that it would take approximately 2.5 work hours per engine to accomplish the proposed on-wing inspection, and that the average labor rate is $60 per work hour. It is estimated that three engines would be found with cracked HPC front drum rotors in the time frame of one year. Approximately 269 engines will be inspected on average per year. The cost of removal and reinstallation of an engine is approximately $10,000, and the cost of replacing the HPC front drum rotor is approximately $750,000. Required replacement parts would cost $356,130 per engine. Based on these figures, the total cost impact per year of the proposed AD for accomplishing initial inspections and replacing HPC front drum rotors, on U.S. operators is estimated to be $3,388,730.

Regulatory Impact

This final rule does not have federalism implications, as defined in Executive Order 13132, because it 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. Accordingly, the FAA has not consulted with state authorities prior to publication of this final rule.

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 the DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and (3) if promulgated, 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 by contacting the Rules Docket at the location provided under the caption ADDRESSES.

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List of Subjects in 14 CFR Part 39

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Adoption of the Amendment

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Accordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration amends part 39 of the Federal Aviation Regulations (

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PART 39—AIRWORTHINESS DIRECTIVES

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1. The authority citation for part 39 continues to read as follows:

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Authority: 49 U.S.C. 106(g), 40113, 44701.

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[Amended]
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2. Section 39.13 is amended adding a new airworthiness directive to read as follows:

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2001-20-13 Pratt & Whitney: Amendment 39-12461. Docket 2000-NE-49-AD.

Applicability

This airworthiness directive (AD) applies to Pratt & Whitney (PW) models PW4052, PW4056, PW4060, PW4062, PW4152, PW4156A, PW4158, PW4460, and PW4462 turbofan engines. These engines are installed on but not limited to Boeing 747, 767, McDonnell Douglas MD-11, Airbus Industrie A300, and A310 series airplanes.

Note 1:

This 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 detect premature cracking of the high pressure compressor (HPC) front drum rotor, that could result in an uncontained engine failure and damage to the airplane, accomplish the following:

Initial Inspection

(a) Perform an initial inspection in accordance with the Accomplishment Instructions, On-Wing paragraphs 1 through 13, of Pratt & Whitney (PW) Alert Service Bulletin (ASB) No. PW4ENG A72-722, dated September 29, 2000 or Revision 1, dated June 7, 2001, as follows:

(1) Perform an initial inspection of HPC front drum rotors before accumulating 1,000 cycles-since-new (CSN) within 500 cycles-in-service (CIS) after the effective date of this AD.

(2) If the presence of a crack needs to be confirmed, perform an eddy current inspection (ECI) within five flight cycles.

(3) If the presence of a crack needs to be confirmed and the suspect crack indication extends from the knife edges to the disk radius directly adjacent to the spacer wall of the sixth or seventh stage as shown in Figures 2 and 3 of PW ASB No. PW4ENG A72-722, Revision 1, dated June 7, 2001, the ECI inspection must be accomplished before further flight.

(4) If the presence of a crack is confirmed, remove and replace the HPC front drum rotor with a serviceable part before further flight.

(5) HPC front drum rotors fluorescent penetrant inspected at the last shop visit, as cited in the compliance section of the ASB, within 500 cycles of the publication date of this AD, satisfy the initial inspection requirement.

Repetitive Inspections

(b) Thereafter, perform inspections within 2,200 cycles-since-last-inspection, in accordance with the Accomplishment Instructions, On-Wing paragraphs 1 through 13, of PW ASB No. PW4ENG A72-722, dated September 29, 2000, or Revision 1, dated June 7, 2001.

(1) If the presence of a crack needs to be confirmed, perform an ECI within five flight cycles.

(2) If the presence of a crack needs to be confirmed and the suspect crack indication extends from the knife edges to the disk radius directly adjacent to the spacer wall of the sixth or seventh stage as shown in Figures 2 and 3 of PW ASB No. PW4ENG A72-722, Revision 1, dated June 7, 2001, the ECI inspection must be accomplished before further flight.

(3) If the presence of a crack is confirmed, remove and replace with a serviceable HPC front drum rotor before further flight.

Definition of Suspect Crack Indication

(c) For the purposes of this AD, a suspect crack indication is defined as a response from the visual borescope inspection procedure that denotes the possible presence of a material discontinuity and requires interpretation to determine its significance.

Alternative Methods of Compliance

(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 (ECO). Operators must submit their request through an appropriate Federal Aviation Administration (FAA) Principal Maintenance Inspector, who may add comments and then send it to the Manager, ECO.

Note 2:

Information concerning the existence of approved alternative methods of compliance with this airworthiness directive, if any, may be obtained from the ECO.

Special Flight Permits

(e) Special flight permits may be issued in accordance with §§ 21.197 and 21.199 of the Federal Aviation Regulations (14 CFR 21.197 and 21.199) to operate the airplane to a location where the requirements of this AD can be accomplished.

Documents That Have Been Incorporated By Reference

(f) The inspection must be done in accordance with the following Pratt & Whitney Alert Service Bulletin (ASB) PW4ENG A72-722, dated September 29, 2000 or (ASB) PW4ENG A72-722, Revision 1, dated June 7, 2001.

Document No.PagesRevisionDate
(ASB) PW4ENG A72-722AllOriginalSeptember 29, 2001.
(ASB) PW4ENG A72-7221-41June 7, 2001.
(ASB) PW4ENG A72-7225OriginalSeptember 29, 2000.
(ASB) PW4ENG A72-72261June 7, 2001.
(ASB) PW4ENG A72-7227-9OriginalSeptember 29, 2000.
(ASB) PW4ENG A72-72210-111June 7, 2001.
(ASB) PW4ENG A72-72212-16OriginalSeptember 29, 2000.
(ASB) PW4ENG A72-722171June 7, 2001.
Total pages: 17

This incorporation by reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 51. Copies may be obtained from Pratt & Whitney, 400 Main Street, East Hartford, CT 06108. Copies may be inspected at the FAA, New England Region, Office of the Regional Counsel, 12 New England Executive Park, Burlington, MA; or at the Office of the Federal Register, 800 North Capitol Street, NW, suite 700, Washington, DC.

Effective Date

(g) This amendment becomes effective on November 16, 2001.

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Issued in Burlington, Massachusetts, on October 2, 2001.

Mark C. Fulmer,

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

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[FR Doc. 01-25396 Filed 10-11-01; 8:45 am]

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