Proposed Rule2026-08549
Airworthiness Directives; General Electric Company Engines
Primary source
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Published
May 1, 2026
Issuing agencies
Transportation DepartmentFederal Aviation Administration
Abstract
The FAA proposes to adopt a new airworthiness directive (AD) for certain General Electric Company (GE) Model CF34-1A, CF34-3A, CF34- 3A1, CF34-3A2, and CF34-3B engines. This proposed AD was prompted by a dual engine power loss event and consequent manufacturer investigation, which revealed corrosion in the high-pressure compressor (HPC) case affecting the variable geometry (VG) system. This proposed AD would require performing certain restart tests and, depending on the results of the tests, additional actions. This proposed AD would also require performing a borescope inspection (BSI) of the HPC case for corrosion and, depending on the results, a VG system functional check for pressure evaluation. This proposed AD would also require, depending on inspection results, performing a force gage test on the feedback cable for tightness and a visual inspection of the VG system for obstruction and, if necessary, removal of the engine from service. This proposed AD would also require revising the airworthiness limitations section (ALS) of the existing engine maintenance manual to incorporate the VG system functional check. The FAA is proposing this AD to address the unsafe condition on these products.
Full Text
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<title>Federal Register, Volume 91 Issue 84 (Friday, May 1, 2026)</title>
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[Federal Register Volume 91, Number 84 (Friday, May 1, 2026)]
[Proposed Rules]
[Pages 23377-23380]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2026-08549]
========================================================================
Proposed Rules
Federal Register
________________________________________________________________________
This section of the FEDERAL REGISTER contains notices to the public of
the proposed issuance of rules and regulations. The purpose of these
notices is to give interested persons an opportunity to participate in
the rule making prior to the adoption of the final rules.
========================================================================
Federal Register / Vol. 91, No. 84 / Friday, May 1, 2026 / Proposed
Rules
[[Page 23377]]
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. FAA-2026-3875; Project Identifier AD-2025-01365-E]
RIN 2120-AA64
Airworthiness Directives; General Electric Company Engines
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Notice of proposed rulemaking (NPRM).
-----------------------------------------------------------------------
SUMMARY: The FAA proposes to adopt a new airworthiness directive (AD)
for certain General Electric Company (GE) Model CF34-1A, CF34-3A, CF34-
3A1, CF34-3A2, and CF34-3B engines. This proposed AD was prompted by a
dual engine power loss event and consequent manufacturer investigation,
which revealed corrosion in the high-pressure compressor (HPC) case
affecting the variable geometry (VG) system. This proposed AD would
require performing certain restart tests and, depending on the results
of the tests, additional actions. This proposed AD would also require
performing a borescope inspection (BSI) of the HPC case for corrosion
and, depending on the results, a VG system functional check for
pressure evaluation. This proposed AD would also require, depending on
inspection results, performing a force gage test on the feedback cable
for tightness and a visual inspection of the VG system for obstruction
and, if necessary, removal of the engine from service. This proposed AD
would also require revising the airworthiness limitations section (ALS)
of the existing engine maintenance manual to incorporate the VG system
functional check. The FAA is proposing this AD to address the unsafe
condition on these products.
DATES: The FAA must receive comments on this proposed AD by June 15,
2026.
ADDRESSES: You may send comments, using the procedures found in 14 CFR
11.43 and 11.45, by any of the following methods:
<bullet> Federal eRulemaking Portal: Go to <a href="http://regulations.gov">regulations.gov</a>. Follow
the instructions for submitting comments.
<bullet> Fax: (202) 493-2251.
<bullet> Mail: U.S. Department of Transportation, Docket
Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New
Jersey Avenue SE, Washington, DC 20590.
<bullet> Hand Delivery: Deliver to Mail address above between 9
a.m. and 5 p.m., Monday through Friday, except Federal holidays.
AD Docket: You may examine the AD docket at <a href="http://regulations.gov">regulations.gov</a> under
Docket No. FAA-2026-3875; 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 NPRM, any comments received, and other
information. The street address for Docket Operations is listed above.
Material Incorporated by Reference:
<bullet> For GE material identified in this AD, contact GE, 1
Neumann Way, Cincinnati, OH 45215; phone: (513) 552-3272; email:
<a href="/cdn-cgi/l/email-protection#c2a3b4aba3b6abadaceca4aea7a7b6b1b7b2b2adb0b682fea3e2aab0a7a4ff" http: ge.com">ge.com</a>">aviation.fleetsupport@<a href="http://ge.com">ge.com</a></a>; website: <a href="http://ge.com">ge.com</a>.
<bullet> You may view this material 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 (817) 222-5110.
FOR FURTHER INFORMATION CONTACT: Alexei Marqueen, Aviation Safety
Engineer, FAA, 2200 South 216th Street, Des Moines, WA 98198; phone:
(781) 238-7178; email: <a href="/cdn-cgi/l/email-protection#a4c5c8c1dcc1cd8ad08ac9c5d6d5d1c1c1cae4c2c5c58ac3cbd2"><span class="__cf_email__" data-cfemail="2c4d4049544945025802414d5e5d594949426c4a4d4d024b435a">[email protected]</span></a>.
SUPPLEMENTARY INFORMATION:
Comments Invited
The FAA invites you to send any written relevant data, views, or
arguments about this proposal. Send your comments using a method listed
under the ADDRESSES section. Include ``Docket No. FAA-2026-3875;
Project Identifier AD-2025-01365-E'' at the beginning of your comments.
The most helpful comments reference a specific portion of the proposal,
explain the reason for any recommended change, and include supporting
data. The FAA will consider all comments received by the closing date
and may revise this proposal because of those comments.
Except for Confidential Business Information (CBI) as described in
the following paragraph, and other information as described in 14 CFR
11.35, the FAA will post all comments received, without change, to
<a href="http://regulations.gov">regulations.gov</a>, including any personal information you provide. The
agency will also post a report summarizing each substantive verbal
contact received about this NPRM.
Confidential Business Information
CBI is commercial or financial information that is both customarily
and actually treated as private by its owner. Under the Freedom of
Information Act (FOIA) (5 U.S.C. 552), CBI is exempt from public
disclosure. If your comments responsive to this NPRM contain commercial
or financial information that is customarily treated as private, that
you actually treat as private, and that is relevant or responsive to
this NPRM, it is important that you clearly designate the submitted
comments as CBI. Please mark each page of your submission containing
CBI as ``PROPIN.'' The FAA will treat such marked submissions as
confidential under the FOIA, and they will not be placed in the public
docket of this NPRM. Submissions containing CBI should be sent to
Alexei Marqueen, Aviation Safety Engineer, FAA, 2200 South 216th
Street, Des Moines, WA 98198. Any commentary that the FAA receives
which is not specifically designated as CBI will be placed in the
public docket for this rulemaking.
Background
The FAA received a report that an airplane powered by GE Model
CF34-3B engines experienced an uncommanded simultaneous dual engine in-
flight shutdown. The engine manufacturer investigation revealed
evidence of corrosion in the HPC module. Further analysis indicated
corrosion in the HPC case vane boreholes traditionally associated with
hardware that has been exposed to a saline environment, and pitting
along the HPC case, with the worst corrosion in later stages from
additional oxidation due to higher operating temperatures. While the
investigation has yet to identify a definitive root cause, GE considers
corrosion to be a contributing factor. Corrosion in the HPC case
[[Page 23378]]
variable vane spindle bores can result in restricted range of motion of
the VG system, which can lead to compressor instability at or below
idle speeds and potential loss of engine thrust control. As a result,
GE published service material with inspection instructions to determine
if the VG actuating system is obstructed by corrosion that can reduce
its range of motion. This condition, if not addressed, could result in
loss of engine thrust control and reduced control of the airplane.
The affected population of engines includes the entire GE Model
CF34-3 fleet. GE Model CF34-1A engines have all been converted to CF34-
3A or they are no longer in production or service, but they are
included in the applicability of this proposed AD in case there are any
remaining GE Model CF34-1A engines that are unaccounted for.
FAA's Determination
The FAA is issuing this NPRM after determining that the unsafe
condition described previously is likely to exist or develop on other
products of the same type design.
Material Incorporated by Reference Under 1 CFR Part 51
The FAA reviewed GE CF34BJ Service Bulletin 72-0347, Revision 02,
dated October 30, 2025. This material specifies procedures for
performing repetitive engine heat soak restart tests for a hung start
and, depending on the results of the tests, engine troubleshooting and
corrective actions. This material also specifies procedures for
performing a borescope inspection (BSI) of the HPC case for corrosion
and, depending on the results of the BSI, a VG system functional check
for pressure evaluation. This material also specifies procedures for
performing a force gage test on the feedback cable for tightness and a
visual inspection of the VG system for obstruction.
The FAA also reviewed MM 05-21-00, ENGINE MAINTENANCE PROGRAM from
GE CF34-3 Maintenance Manual SEI-580, Rev. 49, dated August 1, 2024 (GE
Model CF34-1A, CF34-3A, and CF34-3A2 engines); SM 05-21-00, MAINTENANCE
PROGRAMS from GE CF34-3 Service Manual SEI-780, Rev. 65, dated February
1, 2025 (GE Model CF34-3A1 and CF34-3B engines); and EM 05-21-00
ENGINE--MAINTENANCE PROGRAM from GE CF34RJ Engine Manual SEI-756, Rev.
69, dated February 1, 2025 (GE Model CF34-3A1 and CF34-3B1 engines).
This material specifies procedures for performing VG system inspections
on certain GE Model engines, as applicable.
This material is reasonably available because the interested
parties have access to it through their normal course of business or by
the means identified in the ADDRESSES section.
Proposed AD Requirements in This NPRM
This proposed AD would require performing repetitive engine heat
soak restart tests for a hung start and, depending on the results of
the tests, engine troubleshooting and corrective actions. This proposed
AD would also require performing a borescope inspection (BSI) of the
HPC case for corrosion and, depending on the results of the BSI, a VG
system functional check for pressure evaluation. This proposed AD would
also require, depending on inspection results, performing a force gage
test on the feedback cable for tightness and a visual inspection of the
VG system for obstruction and, if necessary, removal of the engine from
service. This proposed AD would also require revising the ALS of the
existing engine maintenance manual to incorporate the VG system
functional check.
Costs of Compliance
The FAA estimates that this AD, if adopted as proposed, would
affect 1,152 engines installed on airplanes of U.S. registry.
The FAA estimates the following costs to comply with this proposed
AD:
Estimated Costs
----------------------------------------------------------------------------------------------------------------
Cost per Cost on U.S.
Action Labor cost Parts cost product operators
----------------------------------------------------------------------------------------------------------------
Engine heat soak restart test (per test). 8 work-hours x $85 per hour $0 $680 $783,360
= $680.
BSI of the HPC case...................... 8 work-hours x $85 per hour 0 680 783,360
= $680.
Revise the ALS........................... 1 work-hour x $85.00 per 0 85 97,920
hour = $85.
----------------------------------------------------------------------------------------------------------------
The FAA estimates the following costs to do any necessary repairs
or checks that would be required based on the results of the proposed
inspection. The agency has no way of determining the number of engines
that might need these repairs or checks:
On-Condition Costs
----------------------------------------------------------------------------------------------------------------
Cost per
Action Labor cost Parts cost product
----------------------------------------------------------------------------------------------------------------
VG system functional check..................... 8 work-hours x $85 per hour = $680 $0 $680
Force gage test on feedback cable.............. 8 work-hours x $85 per hour = $680 0 680
Visual inspection of VG system................. 8 work-hours x $85 per hour = $680 0 680
Repair of tight feedback cable or obstruction 8 work-hours x $85 per hour = $680 0 680
in VG system.
Engine troubleshooting......................... 8 work-hours x $85 per hour = $680 0 680
Engine replacement............................. 192 work-hours x $85 per hour = 600,000 616,320
$16,320.
----------------------------------------------------------------------------------------------------------------
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
[[Page 23379]]
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
The FAA 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 this proposed
regulation:
(1) Is not a ``significant regulatory action'' under Executive
Order 12866,
(2) Would not affect intrastate aviation in Alaska, 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.
List of Subjects in 14 CFR Part 39
Air transportation, Aircraft, Aviation safety, Incorporation by
reference, Safety.
The Proposed Amendment
Accordingly, under the authority delegated to me by the
Administrator, the FAA proposes to amend 14 CFR part 39 as follows:
PART 39--AIRWORTHINESS DIRECTIVES
0
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]
0
2. The FAA amends Sec. 39.13 by adding the following new airworthiness
directive:
General Electric Company: Docket No. FAA-2026-3875; Project
Identifier AD-2025-01365-E.
(a) Comments Due Date
The FAA must receive comments on this airworthiness directive
(AD) by June 15, 2026.
(b) Affected ADs
None.
(c) Applicability
This AD applies to the following General Electric Company (GE)
Model engines:
(1) CF34-1A, CF34-3A, and CF34-3A2 engines with engine serial
numbers (ESN) 350103 through 350525.
(2) CF34-3A1 engines with ESN 807001 through 807661.
(3) CF34-3B engines with ESN 872001 through 873999, 950000
through 950999, and 801001 through 801714.
(d) Subject
Joint Aircraft System Component (JASC) Code 7230, Turbine Engine
Compressor Section.
(e) Unsafe Condition
This AD was prompted by a dual engine power loss event and
consequent manufacturer investigation, which revealed corrosion in
the high-pressure compressor (HPC) case affecting the variable
geometry (VG) system. The FAA is issuing this AD to detect corrosion
in the HPC case that can restrict VG system movement, which can lead
to compressor instability at or below idle speeds. The unsafe
condition, if not addressed, could result in loss of engine thrust
control and reduced control of the airplane.
(f) Compliance
Comply with this AD within the compliance times specified,
unless already done.
(g) Definitions
For the purpose of this AD:
(1) Group 1 engines are engines with 12 months rolling average
utilization of less than 250 hours per year.
(2) Group 2 engines are engines with 12 months rolling average
utilization of more than 250 hours per year.
(3) Group 3 engines are spare engines or engines that are
switched between two different aircraft tail numbers.
(h) Required Actions
(1) Within 3 months after the effective date of this AD and
every 3 months thereafter, perform an engine heat soak restart test
on each engine in accordance with the Accomplishment Instructions,
paragraph 3.B.(1), of GE Service Bulletin (SB) CF34-BJ 72-0347
Revision 02, dated October 30, 2025 (GE SB CF34-BJ 72-0347 R02). If
a hung start is experienced, before further flight, troubleshoot the
engine in accordance with the Accomplishment Instructions, paragraph
3.B.(2), of GE SB CF34-BJ 72-0347 R02.
(2) Within the applicable time specified in paragraphs (h)(2)(i)
through (iii) of this AD, perform a borescope inspection (BSI) of
the high-pressure compressor (HPC) case in accordance with the
Accomplishment Instructions, paragraph 3.C, of GE SB CF34-BJ 72-0347
R02. If the applicable engine group cannot be determined due to lack
of available data, use Group 1 engines as the applicable condition
for the engine.
(i) For Group 1 engines, within 12 months after the effective
date of this AD.
(ii) For Group 2 engines, within 24 months after the effective
date of this AD.
(iii) For Group 3 engines, before further flight after the
effective date of this AD.
(3) If, during the heat soak restart test or the engine
troubleshooting required by paragraph (h)(1) of this AD, or during
the BSI required by paragraph (h)(2) of this AD, corrosion is found,
before further flight, perform a variable geometry (VG) system
functional check in accordance with the Accomplishment Instructions,
paragraph 3.D, of GE SB CF34-BJ 72-0347 R02.
(4) If, during the VG system functional check required by
paragraph (h)(3) of this AD, the pressure necessary to fully extend
or fully retract the actuator is more than 65 psi (448 kPa), before
further flight, perform a force gage test on the feedback cable and
a visual inspection of the VG system in accordance with the
Accomplishment Instructions, paragraph 3.E.(1)(a) and 3.E.(1)(a)(1),
of GE SB CF34-BJ 72-0347 R02. If a tight feedback cable or an
obstruction in the VG system is found, before further flight, repair
the part in accordance with the Accomplishment Instructions,
paragraph 3.E.(1)(a)(1), of GE SB CF34-BJ 72-0347 R02.
(5) If, after performing the actions required by paragraph
(h)(4) of this AD, the pressure necessary to fully extend or fully
retract the actuator is more than 65 psi (448 kPa), remove the
engine from service.
(6) Within 12 months after the effective date of this AD, revise
the Airworthiness Limitations Section (ALS) of the existing CF34-3
Business Jet Engine Manual and the operator's existing approved
maintenance program or inspection program, as applicable, by
incorporating the information specified in Section 9. of MM 05-21-
00, ENGINE MAINTENANCE PROGRAM from GE CF34-3 Maintenance Manual
SEI-580, Rev. 49, dated August 1, 2024, and Section 8. of SM 05-21-
00, MAINTENANCE PROGRAMS from GE CF34-3 Service Manual SEI-780, Rev.
65, dated February 1, 2025.
(7) Within 12 months after the effective date of this AD, revise
the ALS of the existing CF34-3 Regional Jet (RJ) EM and the
operator's existing approved maintenance program or inspection
program, as applicable, by incorporating the information specified
in Section 11. of EM 05-21-00 ENGINE--MAINTENANCE PROGRAM from GE
CF34RJ Engine Manual SEI-756, Rev. 69, dated February 1, 2025.
(i) Terminating Action
Performing a BSI of the HPC case in accordance with paragraph
(h)(2) of this AD constitutes terminating action for the repetitive
heat soak test restart required by paragraph (h)(1) of this AD for
Group 1 or Group 2 engines, as applicable. Group 3 engines are not
subject to repetitive heat soak restart tests.
(j) Credit for Previous Actions
You may take credit for the actions required by paragraphs
(h)(1) through (5) of this AD if you removed and repaired the
following part numbers (P/N) within 48 months prior to the effective
date of this AD using GE SEI-582, 72-31-00, REPAIR, dated September
15, 2001; or GE SEI-782, HMM 72-32-16, REPAIR 07, Rev 65, dated
February 1, 2025; or GE SEI-782, HMM 72-32-17, REPAIR 07, Rev 65,
dated February 1, 2025, at an approved Maintenance Repair and
Overhaul (MRO) shop:
[[Page 23380]]
(1) HPC lower case P/N 6040T84P01 and 6052T48P01.
(2) HPC upper case P/N 6040T84P02 and 6052T48P02.
(3) Compressor case assemblies P/N 4922T71G01, 5088T55G01,
5088T55G02, 5088T55G03, 6078T70G01, 6078T70G02, and 6078T70G03.
(k) Alternative Methods of Compliance (AMOCs)
The Manager, AIR-520 Continued Operational Safety Branch, FAA,
has the authority to approve AMOCs for this AD, if requested using
the procedures found in 14 CFR 39.19. In accordance with 14 CFR
39.19, send your request to your principal inspector or local Flight
Standards District Office, as appropriate. If sending information
directly to the manager of the AIR-520 Continued Operational Safety
Branch, send it to the attention of the person identified in
paragraph (l)(2) of this AD and email to: <a href="/cdn-cgi/l/email-protection#a2e3efede1e2c4c3c38cc5cdd4"><span class="__cf_email__" data-cfemail="2e6f63616d6e484f4f00494158">[email protected]</span></a>. Before using
any approved AMOC, notify your appropriate principal inspector, or
lacking a principal inspector, the manager of the local flight
standards district office/certificate holding district office.
(l) Additional Information
(1) For more information about this AD, Alexei Marqueen,
Aviation Safety Engineer, FAA, 2200 South 216th Street, Des Moines,
WA 98198; phone: (781) 238-7178; email: <a href="/cdn-cgi/l/email-protection#9ffef3fae7faf6b1ebb1f2feedeeeafafaf1dff9fefeb1f8f0e9"><span class="__cf_email__" data-cfemail="fb9a979e839e92d58fd5969a898a8e9e9e95bb9d9a9ad59c948d">[email protected]</span></a>.
(2) Material identified in this AD that is not incorporated by
reference is available at the address specified in paragraph (m)(3)
of this AD.
(m) Material Incorporated by Reference
(1) The Director of the Federal Register approved the
incorporation by reference (IBR) of the material listed in this
paragraph under 5 U.S.C. 552(a) and 1 CFR part 51.
(2) You must use this material as applicable to do the actions
required by this AD, unless the AD specifies otherwise.
(i) GE CF34-BJ Service Bulletin 72-0347, Revision 02, dated
October 30, 2025.
(ii) MM 05-21-00, ENGINE MAINTENANCE PROGRAM from GE CF34-3
Maintenance Manual SEI-580, Rev. 49, dated August 1, 2024.
(iii) SM 05-21-00, MAINTENANCE PROGRAMS from GE CF34-3 Service
Manual SEI-780, Rev. 65, dated February 1, 2025.
(iv) EM 05-21-00 ENGINE--MAINTENANCE PROGRAM from GE CF34RJ
Engine Manual SEI-756, Rev. 69, dated February 1, 2025.
(3) For GE material identified in this AD, contact General
Electric Company, 1 Neumann Way, Cincinnati, OH 45215; phone: (513)
552-3272; email: <a href="/cdn-cgi/l/email-protection#cfaeb9a6aebba6a0a1e1a9a3aaaabbbcbabfbfa0bdbb8ff3aeefa7bdaaa9f2" http: ge.com">ge.com</a>">aviation.fleetsupport@<a href="http://ge.com">ge.com</a></a>; website: <a href="http://ge.com">ge.com</a>.
(4) You may view this material 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 (817) 222-5110.
(5) You may view this material at the National Archives and
Records Administration (NARA). For information on the availability
of this material at NARA, visit <a href="http://www.archives.gov/federal-register/cfr/ibr-locations">www.archives.gov/federal-register/cfr/ibr-locations</a> or email <a href="/cdn-cgi/l/email-protection#4c2a3e6225223f3c292f382523220c222d3e2d622b233a"><span class="__cf_email__" data-cfemail="1b7d69357275686b7e786f7274755b757a697a357c746d">[email protected]</span></a>.
Issued on April 24, 2026.
Brian Knaup,
Acting Deputy Director, Integrated Certificate Management Division,
Aircraft Certification Service.
[FR Doc. 2026-08549 Filed 4-30-26; 8:45 am]
BILLING CODE 4910-13-P
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