DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2019-0919; Project Identifier 2019-NE-24-AD; Amendment
39-21714; AD 2021-18-13]
RIN 2120-AA64

Airworthiness Directives; General Electric Company Turbofan
Engines

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule.

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SUMMARY: The FAA is adopting a new airworthiness directive (AD) for all
General Electric Company (GE) CF34-8 model turbofan engines with a
certain outer shell combustion liner (combustion outer liner shell)
installed. This AD was prompted by two in-flight engine shutdowns
(IFSDs) that occurred as a result of failures of the combustion outer
liner shell. This AD requires a borescope inspection (BSI) or visual
inspection of the combustion outer liner shell and, depending on the
results of the inspection, possible replacement of the combustion outer
liner shell. The FAA is issuing this AD to address the unsafe condition
on these products.

DATES: This AD is effective October 22, 2021.
The Director of the Federal Register approved the incorporation by
reference of certain publications listed in this AD as of October 22,
2021.

ADDRESSES: For service information identified in this final rule,
contact General Electric Company, GE Aviation, Room 285, 1 Neumann Way,
Cincinnati, OH 45215; phone: (513) 552-3272; email:
aviation.fleetsupport@ge.com. You may view this service information at
the FAA, Airworthiness Products Section, Operational Safety Branch,
1200 District Avenue, Burlington, MA 01803. For information on the
availability of this material at the FAA, call (781) 238-7759. It is
also available at https://www.regulations.gov by searching for and
locating Docket No. FAA-2019-0919.

Examining the AD Docket

You may examine the AD docket at https://www.regulations.gov by
searching for and locating Docket No. FAA-2019-0919; or in person at
Docket Operations between 9 a.m. and 5 p.m., Monday through Friday,
except Federal holidays. The AD docket contains this final rule, any
comments received, and other information. The address for Docket
Operations is U.S. Department of Transportation, Docket Operations, M-
30, West Building Ground Floor, Room W12-140, 1200 New Jersey Avenue
SE, Washington, DC 20590.

FOR FURTHER INFORMATION CONTACT: Scott Stevenson, Aviation Safety
Engineer, ECO Branch, FAA, 1200 District Avenue, Burlington, MA 01803;
phone: (781) 238-7132; fax: (781) 238-7199; email:
Scott.M.Stevenson@faa.gov.

SUPPLEMENTARY INFORMATION:

Background

The FAA issued a notice of proposed rulemaking (NPRM) to amend 14
CFR part 39 by adding an AD that would apply to all CF34-8C1, CF34-8C5,
CF34-8C5A1, CF34-8C5B1, CF34-8C5A2, CF34-8C5A3, CF34-8E2, CF34-8E2A1,
CF34-8E5, CF34-8E5A1, CF34-8E5A2, CF34-8E6, and CF34-8E6A1 model
turbofan engines with a certain combustion outer liner shell installed.
The NPRM published in the Federal Register on January 10, 2020 (85 FR
1292). The NPRM was prompted by reports of two IFSDs on GE CF34-8C and
-8E model turbofan engines. These IFSDs were due to the cracking and
collapsing of the combustion outer liner shell, which resulted in
thermal distress of the high-pressure turbine and low-pressure turbine
(LPT) including burn-through of the LPT case. In the NPRM, the FAA
proposed to require a BSI or visual inspection of the combustion outer
liner shell and, depending on the results of the inspection, possible
replacement of the combustion outer liner shell. The FAA is issuing
this AD to address the unsafe condition on these products.

Discussion of Final Airworthiness Directive

Comments

The FAA received comments from four commenters. The commenters were
Horizon Air, Japan Airlines, Endeavor Air, and the Air Line Pilots
Association, International (ALPA). The following presents the comments
received on the NPRM and the FAA's response to each comment.

Request To Change the Initial Compliance Time

Horizon Air requested the FAA revise the initial inspection
threshold in proposed paragraph (g)(2) of the NPRM to ``17,499 flight
hours (FHs) time since new (TSN) or time since repair (TSR), or 12,000
flight cycles (FCs) TSN or TSR, whichever occurs later.'' Horizon Air
reasoned that the initial inspection threshold in paragraph (g)(2) of
the proposed AD would unfairly penalize operators, like Horizon Air,
with high FH to FC ratios. Horizon Air further stated that using the
higher FH to FC ratios, the proposed 17,499 FHs TSN or TSR inspection
threshold would equate to approximately 11,000 engine FCs. This FC
value is substantially below the GE targeted initial engine shop visit
threshold of 12,000 to 14,000 FCs and would potentially result in a
significant increase in the number of engine shop visits over the 6- to
12-year operating lifespan of each engine.
The FAA partially agrees. While the failure mode is partially
related to FCs, the compliance is published in FHs to align with
existing maintenance intervals. Incorporating both measures as
intervals into this AD is impractical; however, operators may request
an alternative method of compliance (AMOC) in accordance with the
procedures specified in paragraph (k) of this AD to use alternate
intervals. The FAA did not change this AD as a result of this comment.

Request To Change the Installation Prohibition

Horizon Air requested the FAA revise paragraph (h), Installation
Prohibition, as proposed in the NPRM, so it does not conflict with the
proposed required actions specified in paragraph (g)(1) of the NPRM.
Horizon Air stated that paragraph (h) of the proposed AD prohibits
installation of a combustion outer liner shell with greater than 17,500
FHs TSN or TSR, without first inspecting it in accordance with
paragraph (g)(1) of the proposed AD. However, paragraph (g)(1) of the
proposed AD requires inspection of the combustion outer liner shell
within 500 engine FHs TSN or TSR for those combustion outer liner
shells that have accumulated 17,500 FHs TSN or TSR. Horizon Air
concluded that the 18,000 FHs TSN or TSR limitation specified in
paragraph (g)(1) of the proposed AD conflicts with the 17,500 FHs TSN
or TSR limit specified in paragraph (h) of the proposed AD.
The FAA disagrees. The initial inspection threshold is 17,500 FHs
for affected engines. This AD provides a grace period of 500 FHs for
in-service engines to prevent the unintentional grounding of airplanes
with affected engines. The FAA did not change this AD as a result of
this comment.

Request To Include a Terminating Action

Horizon Air requested the FAA petition GE for a terminating action
to the inspection requirements in the proposed AD. Horizon Air
commented the financial cost and maintenance burden of performing the
repetitive inspections are significant.
The FAA disagrees. The FAA considers this AD to be interim action
and will consider further rulemaking if the manufacturer develops a
terminating action. The FAA included all estimated costs in the Costs
of Compliance section in the preamble of this AD. The FAA did not
change this AD as a result of this comment.

Request To Revise Service Information References

Horizon Air, Japan Airlines, and Endeavor Air requested the FAA
update references to GE CF34-8E Alert Service Bulletin (SB) 72-A0221
and GE CF34-8C Alert SB 72-A0335 in the Required Actions section,
paragraph (g), of the proposed AD. Japan Airlines requested that GE
CF34-8E-AL S/B 72-A0221, Original Issue, dated June 27, 2019, be added
to the compliance paragraphs because the Original Issue and R01 have
the same inspection methods and limits. Horizon Air requested that the
FAA reference only GE CF34-8E Alert SB 72-A0221 R01 in paragraph (g) of
the proposed AD and add a Previous Credit section to allow previous
compliance using the Original Issue. Endeavor Air requested that the
FAA reference the latest revision of GE CF34-8C Alert SB 72-A0335 in
proposed paragraph (g). Endeavor Air indicated that GE planned to issue
R02 of CF34-8C Alert SB 72-A0335 on February 24, 2020.
The FAA agrees to reference the latest revision of these Alert SBs,
which is R02 for both GE CF34-8C Alert SB 72-A0335 and GE CF34-8E Alert
SB 72-A0221, in paragraph (g) of this AD. The FAA disagrees with the
need to reference prior revisions of these Alert SBs in paragraphs (g)
of this AD but agrees to add Credit for Previous Actions, paragraph
(j), to this AD to allow credit for performing inspections prior to the
effective date of this AD. These changes impose no additional burden on
operators who are required to comply with this AD.

Request To Clarify Compliance

Japan Airlines requested that the FAA clarify whether the
inspection should occur ``before'' or ``within'' 500 FHs after the
effective date of this AD. Japan Airlines reasoned that the service
bulletin specifies to inspect ``before'' 500 FHs, while the NPRM
proposed to inspect ``within'' 500 FHs.
The FAA agrees. The FAA revised Required Actions, paragraphs (g)(1)
and (2) of this AD to specify, ``before accumulating 500 engine FHs.''

Support for the AD

ALPA expressed support for the NPRM as written.

Conclusion

The FAA reviewed the relevant data, considered any comments
received, and determined that air safety requires adopting this AD as
proposed. Accordingly, the FAA is issuing this AD to address the unsafe
condition on these products. Except for minor editorial changes, and
any other changes described previously, this AD is adopted as proposed
in the NPRM. None of the changes will increase the economic burden on
any operator.

Related Service Information Under 1 CFR Part 51

The FAA reviewed General Electric CF34-8C Alert SB 72-A0335 R02 and
General Electric CF34-8E Alert SB 72-A0221 R02, both dated February 25,
2020. The Alert SBs specify procedures for performing a BSI of the
combustion outer liner shell. These documents are distinct since they
apply to different engine models. This service information is
reasonably available because the interested parties have access to it
through their normal course of business or by the means identified in
ADDRESSES.

Interim Action

The FAA considers this AD to be an interim action. If final action
is later identified, the FAA might consider further rulemaking.

Costs of Compliance

The FAA estimates that this AD affects 1,535 engines installed on
airplanes of U.S. registry.
The FAA estimates the following costs to comply with this AD:

Estimated Costs

The FAA estimates the following costs to do any necessary
replacements that would be required based on the results of the
inspection. The agency has no way of determining the number of engines
that might need this replacement:

On-Condition Costs

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.
The FAA is 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

This AD will not have federalism implications under Executive Order
13132. This AD 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.
For the reasons discussed above, I certify that this AD:
(1) Is not a ``significant regulatory action'' under Executive
Order 12866,
(2) Will not affect intrastate aviation in Alaska, 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.

List of Subjects in 14 CFR Part 39

Air transportation, Aircraft, Aviation safety, Incorporation by
reference, Safety.

The Amendment

Accordingly, under the authority delegated to me by the
Administrator, the FAA amends 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. The FAA amends Sec. 39.13 by adding the following new airworthiness
directive: