Proposed Rule2025-05490
Airworthiness Directives; The Boeing Company Airplanes
Primary source
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Published
April 1, 2025
Issuing agencies
Transportation DepartmentFederal Aviation Administration
Abstract
The FAA proposes to adopt a new airworthiness directive (AD) for certain The Boeing Company Model 757 airplanes. This proposed AD was prompted by reports of precoolers that failed due to a wear-out condition, combined with latently failed overheat detection thermal switches. This proposed AD would require an inspection for heat damage on the engine strut structure, repetitive tests of the thermal switch temperature and ground wires, replacement of the precooler on Model 757-300 airplanes, and applicable on-condition actions. The FAA is proposing this AD to address the unsafe condition on these products.
Full Text
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<title>Federal Register, Volume 90 Issue 61 (Tuesday, April 1, 2025)</title>
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[Federal Register Volume 90, Number 61 (Tuesday, April 1, 2025)]
[Proposed Rules]
[Pages 14346-14349]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2025-05490]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. FAA-2025-0474; Project Identifier AD-2024-00777-T]
RIN 2120-AA64
Airworthiness Directives; The Boeing Company Airplanes
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Notice of proposed rulemaking (NPRM).
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SUMMARY: The FAA proposes to adopt a new airworthiness directive (AD)
for certain The Boeing Company Model 757 airplanes. This proposed AD
was prompted by reports of precoolers that failed due to a wear-out
condition, combined with latently failed overheat detection thermal
switches. This proposed AD would require an inspection for heat damage
on the engine strut structure, repetitive tests of the thermal switch
temperature and ground wires, replacement of the precooler on Model
757-300 airplanes, and applicable on-condition actions. 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 May 16,
2025.
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-2025-0474; 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 Boeing material identified in this proposed AD,
contact Boeing Commercial Airplanes, Attention: Contractual & Data
Services (C&DS), 2600 Westminster Blvd., MC 110-SK57, Seal Beach, CA
90740-5600; telephone 562-797-1717; website <a href="http://myboeingfleet.com">myboeingfleet.com</a>.
<bullet> You may view this material at the FAA, Airworthiness
Products Section, Operational Safety Branch, 2200 South 216th St., Des
Moines, WA. For information on the availability of this material at the
FAA, call 206-231-3195. It is also available at <a href="http://regulations.gov">regulations.gov</a> under
Docket No. FAA-2025-0474.
FOR FURTHER INFORMATION CONTACT: Kathryn Hill, Aviation Safety
Engineer, FAA, 2200 South 216th St., Des Moines, WA 98198; phone: 206-
231-3626; email: <a href="/cdn-cgi/l/email-protection#5b103a2f33292235751a75133237371b3d3a3a753c342d"><span class="__cf_email__" data-cfemail="622903160a101b0c4c234c2a0b0e0e220403034c050d14">[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 to an address listed
under the ADDRESSES section. Include ``Docket No. FAA-2025-0474;
Project Identifier AD-2024-00777-T'' 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 amend 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
[[Page 14347]]
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
Kathryn Hill, Aviation Safety Engineer, FAA, 2200 South 216th St., Des
Moines, WA 98198; phone: 206-231-3626; email: <a href="/cdn-cgi/l/email-protection#7833190c100a011656395630111414381e1919561f170e"><span class="__cf_email__" data-cfemail="6a210b1e02181304442b44220306062a0c0b0b440d051c">[email protected]</span></a>.
Any commentary that the FAA receives that is not specifically
designated as CBI will be placed in the public docket for this
rulemaking.
Background
The FAA has received a report of a Model 757-300 airplane that was
taken out of service due to heat damage found on the engine number 1
thrust reverser access door panel. There have been seven instances of
precoolers installed on Model 757-300 airplanes with Rolls-Royce
Deutschland Ltd. & Co. KG Model RB211-535-series engines that failed
due to a wear-out condition. The result of a failed precooler is
leakage of hot air to the strut due to a cracked or ruptured precooler
core near the sideplates. The overheat detection system within an
RB211-535-series engine strut for Model 757-200,-200PF,-200CB, and -300
airplanes contains thermal switches with a latent failure mode. The
combination of a failed precooler and latently failed overheat
detection thermal switches may result in prolonged high temperature
heat exposure on the strut, which could lead to separation of the
engine strut-to-wing box connection.
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 Boeing Alert Requirements Bulletin 757-26A0062 RB,
dated January 17, 2025. This material specifies procedures for a
general visual inspection for heat damage on the left and right engine
strut structure, repetitive thermal switch temperature tests and
continuity tests of the ground wires, and, for Model 757-300 airplanes,
replacement of the precooler at intervals not to exceed 45,000 total
precooler flight hours. This material also specifies procedures for
applicable on-condition actions including repair of structures with
heat damage, replacement of the thermal switch, repair or replacement
of failed circuit wires, and a system test of the strut overheat
detection system, which includes doing applicable corrective actions
until the test is passed. 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 accomplishing the actions specified
in the material already described, except for any differences
identified as exceptions in the regulatory text of this proposed AD.
For information on the procedures and compliance times, see this
material at <a href="http://regulations.gov">regulations.gov</a> under Docket No. FAA-2025-0474.
Interim Action
The FAA considers that this proposed AD would be an interim action.
If final action is later identified, the FAA might consider further
rulemaking then.
Costs of Compliance
The FAA estimates that this AD, if adopted as proposed, would
affect 235 airplanes of U.S. registry. The FAA estimates the following
costs to comply with this proposed AD:
Estimated Costs
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Cost on U.S.
Action Labor cost Parts cost Cost per product operators
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Inspection...................... 12 work-hours x $0................ $1,020............ $239,700.
$85 per hour =
$1,020.
Temperature and continuity test. 20 work-hours x $0................ $1,700............ $399,500 per test
$85 per hour = cycle.
$1,700.
Precooler replacement (21 Model 34 work-hours x Up to $96,675..... Up to $99,565..... Up to $2,090,865
757-300 airplanes). $85 per hour = per replacement
$2,890. cycle.
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The FAA estimates the following costs to do any on-condition
actions that would be required based on the results of the proposed
inspection and proposed test. The agency has no way of determining the
number of airplanes that might need these on-condition actions:
On-Condition Costs *
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Cost per
Action Labor cost Parts cost product
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Strut overheat detection system test.......... 2 work-hours x $85 per hour = $0 $170
$170.
Thermal switch part number (P/N)-003 2 work-hours x $85 per hour = 939 1,109
replacement. $170.
Thermal switch P/N-004 replacement............ 2 work-hours x $85 per hour = 1,704 1,874
$170.
Thermal switch P/N-008 replacement............ 2 work-hours x $85 per hour = 3,810 3,980
$170.
[[Page 14348]]
Wire repair or replacement.................... 2 work-hours x $85 per hour = 0 170
$170.
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* The FAA has received no definitive data on which to base the cost estimates for some of the on-condition
repairs specified in this proposed AD.
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
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:
The Boeing Company: Docket No. FAA-2025-0474; Project Identifier AD-
2024-00777-T.
(a) Comments Due Date
The FAA must receive comments on this airworthiness directive
(AD) by May 16, 2025.
(b) Affected ADs
None.
(c) Applicability
This AD applies to The Boeing Company Model 757-200, -200PF, -
200CB, and -300 series airplanes, certificated in any category, as
identified in Boeing Alert Requirements Bulletin 757-26A0062 RB,
dated January 17, 2025.
(d) Subject
Air Transport Association (ATA) of America Code 26, Fire
protection.
(e) Unsafe Condition
This AD was prompted by reports of precoolers that failed due to
a wear-out condition. The FAA is issuing this AD to address the
combination of a failed precooler and latently failed overheat
detection thermal switches. The unsafe condition, if not addressed,
may result in prolonged high temperature heat exposure on the strut,
which could lead to separation of the engine strut-to-wing box
connection.
(f) Compliance
Comply with this AD within the compliance times specified,
unless already done.
(g) Required Actions
Except as specified in paragraph (h) of this AD: At the
applicable times specified in the ``Compliance'' paragraph of Boeing
Alert Requirements Bulletin 757-26A0062 RB, dated January 17, 2025,
do all applicable actions identified in, and in accordance with, the
Accomplishment Instructions of Boeing Alert Requirements Bulletin
757-26A0062 RB, dated January 17, 2025.
Note 1 to paragraph (g): Guidance for accomplishing the actions
required by this AD can be found in Boeing Alert Service Bulletin
757-26A0062, dated January 17, 2025, which is referred to in Boeing
Alert Requirements Bulletin 757-26A0062 RB, dated January 17, 2025.
(h) Exceptions to Requirements Bulletin Specifications
(1) Where the ``Boeing Recommended Compliance Time'' columns in
the tables under the ``Compliance'' paragraph of Boeing Alert
Requirements Bulletin 757-26A0062 RB, dated January 17, 2025, refer
to ``the Original Issue date of Requirements Bulletin 757-26A0062
RB,'' this AD requires using the effective date of this AD.
(2) Where Boeing Alert Requirements Bulletin 757-26A0062 RB,
dated January 17, 2025, specifies contacting Boeing for repair
instructions, this AD requires doing the repair using a method
approved in accordance with the procedures in paragraph (i) of this
AD.
(i) Alternative Methods of Compliance (AMOCs)
(1) 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
responsible Flight Standards Office, as appropriate. If sending
information directly to the manager of the certification office,
send it to the attention of the person identified in paragraph
(j)(1) of this AD. Information may be emailed to <a href="/cdn-cgi/l/email-protection#6425292b27240205054a030b12"><span class="__cf_email__" data-cfemail="67262a28242701060649000811">[email protected]</span></a>.
(2) Before using any approved AMOC, notify your appropriate
principal inspector, or lacking a principal inspector, the manager
of the responsible Flight Standards Office.
(3) An AMOC that provides an acceptable level of safety may be
used for any repair, modification, or alteration required by this AD
if it is approved by The Boeing Company Organization Designation
Authorization (ODA) that has been authorized by the Manager, AIR-
520, Continued Operational Safety Branch, FAA, to make those
findings. To be approved, the repair method, modification deviation,
or alteration deviation must meet the certification basis of the
airplane, and the approval must specifically refer to this AD.
(j) Related Information
(1) For more information about this AD, contact Kathryn Hill,
Aviation Safety Engineer, FAA, 2200 South 216th St., Des Moines, WA
98198; phone: 206-231-3626; email: <a href="/cdn-cgi/l/email-protection#baf1dbced2c8c3d494fb94f2d3d6d6fadcdbdb94ddd5cc"><span class="__cf_email__" data-cfemail="8dc6ecf9e5fff4e3a3cca3c5e4e1e1cdebececa3eae2fb">[email protected]</span></a>.
(2) Material identified in this AD that is not incorporated by
reference is available at the address specified in paragraph (k)(3)
this AD.
[[Page 14349]]
(k) Material Incorporated by Reference
(1) The Director of the Federal Register approved the
incorporation by reference 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) Boeing Alert Requirements Bulletin 757-26A0062 RB, dated
January 17, 2025.
(ii) [Reserved]
(3) For Boeing material identified in this AD, contact Boeing
Commercial Airplanes, Attention: Contractual & Data Services (C&DS),
2600 Westminster Blvd., MC 110-SK57, Seal Beach, CA 90740-5600;
telephone 562-797-1717; website <a href="http://myboeingfleet.com">myboeingfleet.com</a>.
(4) You may view this material at the FAA, Airworthiness
Products Section, Operational Safety Branch, 2200 South 216th St.,
Des Moines, WA. For information on the availability of this material
at the FAA, call 206-231-3195.
(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#dcbaaef2b5b2afacb9bfa8b5b3b29cb2bdaebdf2bbb3aa"><span class="__cf_email__" data-cfemail="80e6f2aee9eef3f0e5e3f4e9efeec0eee1f2e1aee7eff6">[email protected]</span></a>.
Issued on March 25, 2025.
Victor Wicklund,
Deputy Director, Integrated Certificate Management Division, Aircraft
Certification Service.
[FR Doc. 2025-05490 Filed 3-31-25; 8:45 am]
BILLING CODE 4910-13-P
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