DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. FAA-2021-0503; Project Identifier AD-2021-00163-T]
Airworthiness Directives; The Boeing Company Airplanes
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Notice of proposed rulemaking (NPRM).
SUMMARY: The FAA proposes to supersede Airworthiness Directive
2005-05-18, which applies to certain The Boeing Company Model 737-600,
-700, -700C, -800, and -900 series airplanes. AD 2005-05-18 requires
repetitive inspections for cracking of the webs of the aft pressure
bulkhead at a certain body station, and corrective action if necessary.
Since the FAA issued AD 2005-05-18, cracking was found in that
inspection area on airplanes not identified in the applicability of AD
2005-05-18. This proposed AD would retain the requirements of AD 2005-
05-18, revise the applicability to include additional airplanes, and
add an inspection for existing repairs on the newly added airplanes.
The FAA is proposing this AD to address the unsafe condition on these
DATES: The FAA must receive comments on this proposed AD by August
ADDRESSES: You may send comments, using the procedures found in
11.43 and 11.45, by any of the following methods:
Federal eRulemaking Portal: Go to https://www.regulations.gov. Follow
instructions for submitting comments.
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.
Hand Delivery: Deliver to Mail address above between 9
a.m. and 5 p.m., Monday through Friday, except Federal holidays.
For service information identified in this NPRM, 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; internet https://www.myboeingfleet.com. You may
view this service information 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 https://www.regulations.gov
by searching for and locating Docket No. FAA-2021-0503.
Examining the AD Docket
You may examine the AD docket at https://www.regulations.gov by
searching for and locating Docket No. FAA-2021-0503; 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.
FOR FURTHER INFORMATION CONTACT: Wayne Lockett, Aerospace Engineer,
Airframe Section, FAA, Seattle ACO Branch, 2200 South 216th St., Des
Moines, WA 98198; phone and fax: 206-231-3524; email:
The FAA invites you to send any written relevant data, views, or
arguments about this proposal. Send your comments to an address listed
under ADDRESSES. Include "Docket No. FAA-2021-0503; Project Identifier
AD-2021-00163-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
the 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
https://www.regulations.gov, including any personal information you
provide. The agency will also post a report summarizing each
substantive verbal contact received about this proposed AD.
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 Wayne
Lockett, Aerospace Engineer, Airframe Section, FAA, Seattle ACO Branch,
2200 South 216th St., Des Moines, WA 98198; phone and fax: 206-231-
3524; email: firstname.lastname@example.org. Any commentary that the FAA
receives which is not specifically designated as CBI will be placed in
the public docket for this rulemaking.
The FAA issued AD 2005-05-18, Amendment 39-14007 (70 FR 12410,
March 14, 2005) (AD 2005-05-18), for certain The Boeing Company Model
737-600, -700, -700C, -800, and -900 series airplanes. AD 2005-05-18
was prompted by a report of cracks found, during fatigue testing, at
several of the fastener rows in the web lap splices at the dome apex of
the aft pressure bulkhead. AD 2005-05-18 requires repetitive detailed,
low frequency eddy current (LFEC), and high frequency eddy current
(HFEC) inspections for cracking of the webs of the aft pressure
bulkhead at body station (BS) 1016, and corrective action if necessary.
The FAA issued AD 2005-05-18 to detect and correct fatigue cracks in
the webs of the aft pressure bulkhead, which could result in rapid
decompression of the airplane.
Actions Since AD 2005-05-18 Was Issued
Since the FAA issued AD 2005-05-18, cracking has been found at apex
webs on airplanes outside the applicability of AD 2005-05-18, which
includes line numbers 1 through 1166 inclusive. Line numbers 1167
through 1755 inclusive, which are included in this proposed AD, use a
revised fastener pattern in the 0.032-inch webs that was intended to
correct the cracking addressed by AD 2005-05-18. During the assembly
process on line numbers 1167 through 1755, the fasteners in the apex
dome region are subjected to fuselage pressurization fatigue cycles and
clamp-up stresses. Cracks in the inspection area of AD 2005-05-18 have
been found on airplanes within the range of line numbers 1167 through
inclusive. At one location, the crack was linked from the first to the
second fastener row. This cracking was identified during an inspection
cracking of the web lap splice of the aft pressure bulkhead, as required
by AD 2017-10-22, Amendment 39-18896 (82 FR 23507, May 23, 2017) (AD 2017-
10-22). The inspections and intervals specified in AD 2017-10-22 are not
adequate to address the specific fatigue cracking occurring in the web
apex area that is the subject of this NPRM.
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.
Related Service Information Under 1 CFR Part 51
The FAA reviewed Boeing Alert Service Bulletin 737-53A1251,
Revision 2, dated January 20, 2021. This service information specifies
procedures for a general visual inspection for existing repairs,
repetitive detailed and HFEC inspections for cracks around the web
fasteners, repetitive LFEC inspection for cracks around the hidden web
lap splice fastener locations, and repair of cracks. 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 the ADDRESSES section.
Proposed AD Requirements in This NPRM
Although this proposed AD does not explicitly restate the
requirements of AD 2005-05-18, this proposed AD would retain all of the
requirements of AD 2005-05-18. Those requirements are referenced in the
service information identified previously, which, in turn, is
referenced in paragraph (g) of this proposed AD. This proposed AD would
revise the applicability to include additional airplanes, and add an
inspection for existing repairs on those airplanes. This proposed AD
would also require accomplishment of the actions identified as "RC"
(required for compliance) in the Accomplishment Instructions of Boeing
Alert Service Bulletin 737-53A1251, Revision 2, dated January 20, 2021,
described previously, 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
service information at https://www.regulations.gov by searching for and
locating Docket No. FAA-2021-0503.
Differences Between This Proposed AD and the Service Information
For Group 1 airplanes, the Accomplishment Instructions of Boeing
Alert Service Bulletin 737-53A1251 Revision 2, dated January 20, 2021,
do not include any "RC" (required for compliance) steps. The RC
tagging was inadvertently removed from Boeing Alert Service Bulletin
737-53A1251 Revision 2, dated January 20, 2021. For Group 1 airplanes,
this proposed AD would therefore require treating Step 3.B.2. of the
Accomplishment Instructions of Boeing Alert Service Bulletin 737-
53A1251 Revision 2, dated January 20, 2021, as an RC step.
Costs of Compliance
The FAA estimates that this AD, if adopted as proposed, would affect
744 airplanes of U.S. registry. The FAA estimates the following costs
comply with this proposed AD:
|Detailed, HFEC, and LFEC inspections
||Up to 10 work-hours x $85 per
hour = Up to $850 per inspection cycle
||Up to $850 per inspection cycle
||Up to $632,400 per inspection
|General visual inspection (194
||1 work-hour x $85 per hour =
The FAA estimates the following costs
to do any necessary repairs
that would be required based on the results of the proposed
inspections. The FAA has no way of determining the number of aircraft
that might need these repairs:
||Up to 30 * work-hours
x $85 per hour = Up to $2,550
||Up to $30,000 *
||Up to $32,550 *
* Repair costs will vary depending
on size of the repair required.
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.
The FAA has 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
For the reasons discussed above, I certify that the proposed
(1) Is not a "significant regulatory action" under Executive
(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
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
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:
a. Removing Airworthiness Directive (AD) 2005-05-18, Amendment 39-14007
(70 FR 12410, March 14, 2005), and
b. Adding the following new AD: