AD 2001-20-13

[Federal Register Volume 66, Number 198 (Friday, October 12, 2001)]
[Rules and Regulations]
[Pages 52023-52027]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 01-25396]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 2000-NE-49-AD; Amendment 39-12461; AD 2001-20-13]
RIN 2120-AA64


Airworthiness Directives; Pratt & Whitney PW4000 Series Turbofan 
Engines

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule.

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[[Page 52024]]

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.

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.

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.

[[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.

[[Page 52026]]

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 U.S.C. 106(g), 40113, 44701.


Sec. 39.13  [Amended]

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

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 
Secs. 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.

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             Document No.                  Pages            Revision                         Date
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(ASB) PW4ENG A72-722..................      All     Original................  September 29, 2001.
(ASB) PW4ENG A72-722..................      1-4     1.......................  June 7, 2001.
(ASB) PW4ENG A72-722..................        5     Original................  September 29, 2000.
(ASB) PW4ENG A72-722..................        6     1.......................  June 7, 2001.
(ASB) PW4ENG A72-722..................      7-9     Original................  September 29, 2000.
(ASB) PW4ENG A72-722..................    10-11     1.......................  June 7, 2001.
(ASB) PW4ENG A72-722..................    12-16     Original................  September 29, 2000.
(ASB) PW4ENG A72-722..................       17     1.......................  June 7, 2001.
    Total pages: 17...................
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    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.


[[Page 52027]]


    Issued in Burlington, Massachusetts, on October 2, 2001.
Mark C. Fulmer,
Acting Manager, Engine and Propeller Directorate, Aircraft 
Certification Service.
[FR Doc. 01-25396 Filed 10-11-01; 8:45 am]
BILLING CODE 4910-13-U