[Federal Register: January 27, 2003 (Volume 68, Number 17)]
[Rules and Regulations]
[Page 3805-3808]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr27ja03-1]
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Rules and Regulations
Federal Register
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[[Page 3805]]
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. 2001-NE-19-AD; Amendment 39-13024; AD 2003-02-07]
RIN 2120-AA64
Airworthiness Directives; General Electric Company CF6-50 and
CF6-80C2 Turbofan Engines
AGENCY: Federal Aviation Administration, DOT.
ACTION: Final rule.
-----------------------------------------------------------------------
SUMMARY: This amendment adopts a new airworthiness directive (AD), that
is applicable to General Electric Company CF6-50 and CF6-80C2 turbofan
engines. This amendment requires replacement of certain existing CF6-50
and CF6-80C2 low pressure turbine (LPT) shrouds with new design LPT
shrouds. This amendment is prompted by 37 LPT uncontained events on the
CF6-50, 24 uncontained events on the CF6-80C2 engine models since 1993,
and the development and certification of newly designed shrouds that
will improve LPT containment capability. The actions specified by this
AD are intended to prevent uncontained engine failure and possible
airplane damage.
DATES: Effective March 3, 2003.
ADDRESSES: Information regarding this action may be examined, by
appointment, at the Federal Aviation Administration (FAA), New England
Region, Office of the Regional Counsel, 12 New England Executive Park,
Burlington, MA.
FOR FURTHER INFORMATION CONTACT: Karen Curtis, Aerospace Engineer,
Engine Certification Office, FAA, Engine and Propeller Directorate, 12
New England Executive Park, Burlington, MA 01803-5299; telephone (781)
238-7192; 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 General Electric Company CF6-50 and CF6-80C2 turbofan
engines was published in the Federal Register on May 17, 2001 (66 FR
27475). That action proposed to require replacement of certain existing
CF6-50 and CF6-80C2 LPT shrouds with new design shrouds.
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.
Request Withdrawal of Proposed Rule
Five commenters request that the proposed rule be withdrawn. The
commenters believe that the new LPT shrouds will not prevent or
significantly reduce the occurrence or severity of the more severe (SAE
Category 2 or higher) uncontained events, and therefore, the economic
impact is not justified by this limited improvement in safety. The
commenters provided statistics to show that the vast majority (89%) of
the uncontained LPT events were SAE Category 1 with no aircraft impact,
and were, therefore, no hazard to continued safe flight. Data was also
provided that showed that none of the Category 2 events had caused more
than minor aircraft damage, and that corrective actions (i.e.
inspection or replacement programs; some required by existing AD's)
were available from the manufacturer to address the majority of the
root causes that had led to the Category 2 events.
The FAA partially agrees. The FAA agrees that because the design
criteria for the shrouds is based on ballistic containment
calculations, it is difficult to quantify a benefit for the improved
LPT shrouds for rub-through or push-through events. However, the FAA
disagrees that the improved shrouds will not provide some additional
benefit for those events where the LPT uncontainment was not
exclusively of a ballistic nature. Although the events occurring to-
date have not resulted in significant hazards to continued safe flight,
the potential exists for future events to be more significant.
Therefore, in addition to requiring that the root causes for the
upstream failures that have led to uncontained LPT events be addressed,
the FAA believes that the improved LPT shrouds must be incorporated to
meet the intent of the regulations, which is for the engines to contain
failures at the engine case level.
Extend or Eliminate Compliance End Date
Seven commenters request that the compliance end date be extended
or eliminated. The commenters noted that all of the CF6-50 models would
likely be in compliance by that date based on their estimated shop
visit and LPT exposure rates, but that many CF6-80C2 engines would be
forced off-wing early solely for this compliance, thereby imposing a
significant financial burden that was not included in the economic
analysis of the proposal.
The FAA agrees that the intended improvement in safety can be
achieved by extending the compliance end date to support the normal
shop visit and LPT exposure rates and, therefore, the proposed calendar
end date is changed in the final rule.
Request for Exemption of Certain LPT Cases and LPT Shroud
Configurations
Four commenters request that engines configured with a certain LPT
case configuration and certain LPT shroud configurations be exempt from
the proposed AD. The commenters note that the improved LPT case, part
number (P/N) 1647M68G15, introduced by GE Aircraft Engines Service
Bulletin (GEAE SB) 72-0946 in conjunction with certain LPT shrouds
provides equivalent containment to the older design LPT case with the
newest shrouds referenced by the proposed rule.
The FAA agrees. The manufacturer has provided data to show that
CF6-80C2 engines configured with the later LPT cases and certain LPT
shrouds provide equivalent containment capability. Therefore, CF6-80C2
engines configured with the combination of LPT case, P/N 1647M68G15,
and LPT stage 2 shroud, P/N 1862M62G01 or 1862M62G03; and LPT stage 3
shroud, P/N 1862M63G01 or 1862M63G03; and LPT stage 4 shroud P/N
1862M64G01 or 1862M64G03 are exempted from this rule. The final rule is
revised to reflect this change, and the economic analysis of the final
rule is reduced to reflect this change.
[[Page 3806]]
Request for Relaxed Compliance Requirements
Three commenters request that relaxed compliance requirements be
provided for engines with certain configurations that reduce the
probability of an upstream failure that has been known to result in the
higher severity uncontained LPT events. The commenters believe that
addressing the root causes of the uncontained LPT failures will be more
effective than the new shrouds for improving containment and reducing
the frequency and severity of the events.
The FAA partially agrees. The FAA agrees that upstream failures
that lead to uncontained LPT events must be addressed and has already
mandated corrective actions for many of those known failure mechanisms.
However, as stated in the proposed rule, not all such possible upstream
failure modes can be predicted or anticipated. Therefore, the FAA
disagrees that relaxed compliance schedules for engines configured with
certain root cause fixes will achieve the necessary safety improvement
that will be realized by incorporation of the improved LPT shrouds. No
changes will be made to this AD.
Request for Equivalent Replacement Parts
Five commenters request that any FAA-approved Parts Manufacturing
Approval (PMA) or repaired configurations of the manufacturer's design
be allowed as equivalent replacement parts for the GE service bulletin
parts.
The FAA agrees. The final rule is revised to include all of the
known FAA-approved equivalent parts for each of the engine models as
acceptable configurations.
Service Bulletin Accepted as Compliance to Proposed Rule
One commenter requests that GE CF6-50 SB 72-1170, Revision 1, dated
November 30, 1999, be accepted as compliance for the proposed rule. The
commenter notes that this revision clarifies the engines that are
affected by explicitly listing all of the earlier shroud part numbers
that should be replaced with the new shroud part numbers.
The FAA partially agrees. The FAA agrees that the revised SB
provides additional clarification on the affected engines. However, as
noted in the FAA response to the previous comment on equivalent
replacement parts, there are other parts in addition to those
referenced in that SB that can be used to comply with this AD. The
final rule is changed to eliminate the incorporation by reference of
any version of the SB.
Analysis Request To Quantify Containment Improvement
One commenter requests that an analysis be provided to quantify the
containment improvement provided by the new shrouds. The commenter
believes that the new design shrouds do not improve the containment
capability as intended because the minimum thickness of the shear
section is not changed.
The FAA disagrees. The FAA feels that the containment capability of
the shrouds can not be determined based on shear section thickness
alone. No changes will be made to this AD.
Request for Engine Containment Test
One commenter requests that the OEM be required to perform an
engine containment test to demonstrate the effectiveness of the new
design shrouds. The commenter believes that other OEM's have been
required to perform such tests in order to substantiate improved
containment. The commenter believes that the high cost of compliance
with the proposed rule warrants such a test demonstration.
The FAA does not agree. The regulations for the most part address
primary blade containment. Test demonstrations for secondary failure
modes, due to multiple upstream failures, as in this case, are not
normally required. In addition, the regulations allow the use of
analysis in lieu of a test demonstration, and a test is not always
required for substantiation. No changes will be made to this AD.
Request To Limit the Number of Times a Shroud Can Be Repaired
One commenter requests that the proposed rule be revised to limit
the number of times a shroud can be repaired. The commenter notes, as
stated in the proposal, that multiple repairs can lead to reduced
backsheet thickness and result in reduced containment system
capability.
The FAA partially agrees. The FAA agrees that multiple repairs can
possibly result in reduced backsheet thickness. However, the FAA
disagrees that the specific number of repairs that will result in this
condition can be defined. Instead, the engine manufacturer has made
modifications to the engine manual to require a check of the backsheet
thickness in order to determine the serviceability of the shroud.
Compliance with the revised manual limit will ensure that the minimum
backsheet thickness required to achieve the system containment
capability is maintained. No changes will be made to this AD.
Request for Revision to Notice of Proposed Rulemaking (NPRM)
One commenter requests that the proposed rule be revised to include
improved stage 1 and stage 5 shrouds for the CF6-80C2. The commenter
believes that a recent in-service event indicates that improved
containment is necessary in stages 1 and 5 as well as stages 2, 3, and
4 that have already been proposed. The commenter recommends that an
engineering analysis be performed to verify that these additional
shrouds are adequate to prevent the failure mode recently demonstrated
in plane 5 of the LPT.
The FAA does not agree. The most recent event referred to by this
commenter exhibited an unusual variation of LPT uncontainment in which
an extensive rub-through occurred in plane 5. The shrouds mandated for
incorporation by this rule were redesigned primarily to address
ballistic type containment events at stages where field experience and
the manufacturer's analysis had shown deficiencies. In addition, the
manufacturer has advised the FAA that although new part numbers for
stage 1 and stage 5 LPT shrouds were introduced to the field at the
same time as the stage 2 through 4 shrouds, the redesigns of those
shrouds were made primarily to improve manufacturing and would have no
appreciable affect on ballistic containment capability and no affect on
the rub-through type of failure. Potential redesigns to address the
case rub-through scenario are under consideration. Further rule making
activity to address the rub-through failure scenario will be considered
once redesigns are certified. No changes will be made to this AD.
Request for Additional Replacement Criteria
One commenter requests that replacement be allowed on the basis of
attrition only and that minimum dimensional requirements be defined or
other repairs be developed for the existing shrouds to allow these
shrouds to be returned to service in lieu of the new shrouds. The
commenter believes that an equivalent level of safety can be achieved
with properly repaired or restored versions of the current shroud
design while reducing the cost burden of the proposed rule on the
operators.
The FAA partially agrees. The FAA agrees that the existing shrouds
may be repaired in such a way as to restore the original or achieve the
latest design capability. Such repairs that have been
[[Page 3807]]
approved by the FAA and are known to the FAA have been included as
equivalent parts for compliance with this rule. Also the engine
manufacturer has updated their manuals to include minimum dimensional
requirements for repairability and serviceability of their parts. The
FAA disagrees that replacement by attrition will ensure the intended
improvement in safety. No changes will be made to this 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.
Economic Analysis
There are approximately 5,055 GE CF6-50 and CF6-80C2 turbofan
engines of the affected design in the worldwide fleet. The FAA
estimates that 1,006 engines installed on airplanes of U.S. registry
would be affected by this AD. Because this AD calls for the replacement
of shrouds at piece part exposure, the FAA does not expect that
additional labor costs will be accrued beyond that normally required to
remove the existing shroud. New shrouds will cost approximately $63,250
for the CF6-50 engines, and $87,020 for the CF6-80C2 engines. Based on
these figures, the total cost to retrofit all installed U.S. registered
engines is estimated to be $76,393,990 over an eight year period, or
$9,549,248 annually.
Regulatory Analysis
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) 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.
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.
Sec. 39.13 [Amended]
2. Section 39.13 is amended by adding a new airworthiness directive
to read as follows:
2003-02-07 General Electric Company: Amendment 39-13024. Docket No.
2001-NE-19-AD.
Applicability: This airworthiness directive (AD) is applicable
to General Electric Company (GE) CF6-50 and CF6-80C2 turbofan
engines, except CF6-80C2 engines configured with the combination of
low pressure turbine (LPT) case, part number (P/N) 1647M68G15; and
LPT stage 2 shroud, P/N 1862M62G01 or 1862M62G03; and LPT stage 3
shroud, P/N 1862M63G01 or 1862M63G03; and LPT stage 4 shroud, P/N
1862M64G01 or 1862M64G03. These engines are installed on, but not
limited to, DC-10-15, DC-10-30, MD11, 747, 767, A300 and A310
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: Compliance with this AD is required as indicated,
unless already done.
To prevent uncontained engine failure and possible airplane
damage, do the following:
CF6-80C2 Engines
(a) For CF6-80C2 engines configured with the combination of low
pressure turbine (LPT) case, part number (P/N) 1647M68G15; and LPT
stage 2 shroud, P/N 1862M62G01 or 1862M62G03; and LPT stage 3
shroud, P/N 1862M63G01 or 1862M63G03; and LPT stage 4 shroud, P/N
1862M64G01 or 1862M64G03, no further action is required.
(b) At the next shroud piece-part exposure, but no later than
July 31, 2010, remove existing stage 2, 3, and 4 LPT CF6-80C2
shrouds and replace with new design P/N's listed in the following
Table 1:
Table 1.--CF6-80C2 Acceptable New Shroud Part Numbers
------------------------------------------------------------------------
Stage Part No.
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2................................. 2083M12G01, PCT2083M12G01,
KT2083M12G01, or H042 \1\
3................................. 2083M13G01, PCT2083M13G01,
KT2083M13G01, or H042 \1\
4................................. 2083M14G01, PCT2083M14G01,
KT2083M14G01, or H042 \1\
------------------------------------------------------------------------
\1\ Parts marked with H042, H036, or H037 are parts that have been
repaired by an FAA-approved process specification. In addition to this
process specification marking, each part must show its original (i.e.
before repair) part number and a work order number (i.e. WOxxxxx).
CF6-50 Engines
(c) At the next shroud piece-part exposure, but no later than
July 31, 2010, remove existing stage 1, 2, 3 and 4 LPT CF6-50
shrouds and replace with new design P/N's as listed in the following
Table 2:
Table 2.--CF6-50 Acceptable New Shroud Part Numbers
------------------------------------------------------------------------
Stage Part No.
------------------------------------------------------------------------
1................................. 1822M35G01, PCT1822M35G01,
KT1822M35G01, or H036 \1\
2................................. 1822M36G01, PCT1822M36G01,
KT1822M36G01, or H037 \1\
3................................. 1822M36G02, PCT1822M36G02,
KT1822M36G02, or H037 \1\
4................................. 1822M37G01, PCT1822M37G01,
KT1822M37G01, or H037 \1\
------------------------------------------------------------------------
\1\ Parts marked with H042, H036, or H037 are parts that have been
repaired by an FAA-approved process specification. In addition to this
process specification marking, each part must show its original (i.e.
before repair) part number and a work order number (i.e. WOxxxxx).
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 FAA
Principal Maintenance Inspector, who may add comments and then send
it to the Manager, ECO.
[[Page 3808]]
Note 2: Information concerning the existence of approved
alternative methods of compliance with this airworthiness directive,
if any, may be obtained from ECO.
Special Flight Permits
(e) Special flight permits may be issued in accordance with
Sec. Sec. 21.197 and 21.199 of the Federal Aviation Regulations (14
CFR 21.197 and 21.199) to operate the aircraft to a location where
the requirements of this AD can be done.
Effective Date
(f) This amendment becomes effective on March 3, 2003.
Issued in Burlington, Massachusetts, on January 17, 2003.
Francis A. Favara,
Acting Manager, Engine and Propeller Directorate, Aircraft
Certification Service.
[FR Doc. 03-1675 Filed 1-24-03; 8:45 am]
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