DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2021-0157; Project Identifier AD-2020-00483-T;
Amendment 39-21806; AD 2021-23-08]
RIN 2120-AA64

Airworthiness Directives; Learjet Inc. Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule.

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SUMMARY: The FAA is adopting a new airworthiness directive (AD) for
certain Learjet Inc. (Learjet) Model 45 airplanes. This AD was prompted
by reports of corrosion found on the upper surface of the lower center
wing mid spar splice plate. This AD requires repetitively inspecting
the center wing area for corrosion and deterioration of protective
treatments, removing any corrosion, and treating any deteriorated
areas. The FAA is issuing this AD to address the unsafe condition on
these products.

DATES: This AD is effective January 10, 2022.
The Director of the Federal Register approved the incorporation by
reference of certain publications listed in this AD as of January 10,
2022.

ADDRESSES: For service information identified in this final rule,
contact Learjet Inc., One Learjet Way, Wichita, KS 67209; phone: (316)
946-2000; email: ac.ict@aero.bombardier.com; website: https://
businessaircraft.bombardier.com/en/aircraft/learjet.html. You may view
this referenced service information at the FAA, Airworthiness Products
Section, Operational Safety Branch, 901 Locust, Kansas City, MO 64106.
For information on the availability of this material at the FAA, call
(816) 329-4148.

Examining the AD Docket

You may examine the AD docket at https://www.regulations.gov by
searching for and locating Docket No. FAA-2021-0157; 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: Tara Shawn, Aviation Safety Engineer,
Wichita ACO Branch, FAA, 1801 Airport Road, Wichita, KS 67209; phone:
(316) 946-4141; fax: (316) 946-4107; email: tara.shawn@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 certain serial numbered
Learjet Inc. (Learjet) Model 45 (Learjet 40), Model 45 (Learjet 45),
Model 45 (Learjet 70), and Model 45 (Learjet 75) airplanes. The NPRM
published in the Federal Register on July 28, 2021 (86 FR 40379). The
NPRM was prompted by a report from Learjet of corrosion found in the
center wing area of a Model 45 (Learjet 45) airplane. Exfoliating
corrosion was found on the upper surface of the lower center wing mid
spar splice plate during unrelated maintenance. The corrosion appeared
to extend half way through the thickness of the splice plate. Since the
initial report, the FAA has received 23 additional reports of corrosion
from Learjet.
The FAA determined areas of the wing center section are not sealed
against the elements; in addition, the fuselage has drain holes that
allow condensation to drain into the center wing. The accumulation and
retention of moisture in the center wing section may lead to corrosion.
In the NPRM, the FAA proposed to require repetitively inspecting the
center wing area for corrosion and deterioration of protective
treatments, removing any corrosion, and treating any deteriorated
areas. This condition, if not addressed, could result in failure of the wing
centerline joint and lead to partial wing separation with consequent
loss of control of the airplane.

Discussion of Final Airworthiness Directive

Comments

The FAA received one comment from an individual. The following
presents the comment received on the NPRM and the FAA's response to the
comment.
An individual requested the FAA allow credit for previous visual
inspections using Inspection Reference Number (IRN) 5710190. The
commenter stated that IRN 5710190 requires the same inspection as the
applicable service bulletin. The commenter noted that while some
operators might not have used the service bulletin listed in paragraph
(k) of the NPRM, operators of aircraft over 8 years old will have used
IRN 5710190.
The FAA agrees and has added the applicable maintenance manual
references for IRN 5710190 to paragraph (k) of this AD, which provides
credit for previous actions.

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 the 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 the following service documents required for
compliance with this AD:
Bombardier Learjet 40 Service Bulletin 40-57-06, Revision
1, dated October, 26, 2020;
Bombardier Learjet 45 Service Bulletin 45-57-13, Revision
1, dated October, 26, 2020;
Bombardier Learjet 70 Service Bulletin 70-57-02, Revision
1, dated October, 26, 2020; and
Bombardier Learjet 75 Service Bulletin 75-57-01, Revision
2, dated April 19, 2021.
As applicable to the model configuration specified, each service
bulletin contains procedures for inspecting for corrosion and
deterioration of protective treatments of the center wing area from the
front spar to the rear spar between wing stations 33.00L to 33.00R,
treating deteriorated areas, and removing any corrosion. Bombardier
Learjet 75 Service Bulletin 75-57-01, Revision 2, dated April 19, 2021,
does not apply to newly- manufactured airplanes, since Learjet added
this inspection to the Airworthiness Limitation Section, which will be
delivered with new airplanes starting at S/N 45-597.
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.

Costs of Compliance

The FAA estimates that this AD affects 450 airplanes of U.S.
registry.
The FAA estimates the following costs to comply with this AD:

Estimated costs

The extent of corrosion and deterioration of protective treatments
may vary significantly from airplane to airplane. The FAA has no way of
determining how much damage may be found on each airplane, the cost to
remove the corrosion or treat deteriorated areas (or replacing the
part, if needed), or the number of airplanes that may require repair.
If corrosion is found and removed, the FAA estimates that it would
take 2 work-hours per airplane to provide data to Learjet. With an
average labor rate of $85 per work-hour, the FAA estimates a cost of
$170 per airplane.

Paperwork Reduction Act

A federal agency may not conduct or sponsor, and a person is not
required to respond to, nor shall a person be subject to a penalty for
failure to comply with a collection of information subject to the
requirements of the Paperwork Reduction Act unless that collection of
information displays a currently valid OMB Control Number. The OMB
Control Number for this information collection is 2120-0056. Public
reporting for this collection of information is estimated to take
approximately 3 hours per response, including the time for reviewing
instructions, searching existing data sources, gathering and
maintaining the data needed, and completing and reviewing the
collection of information. All responses to this collection of
information are mandatory. Send comments regarding this burden estimate
or any other aspect of this collection of information, including
suggestions for reducing this burden to: Information Collection
Clearance Officer, Federal Aviation Administration, 10101 Hillwood
Parkway, Fort Worth, TX 76177-1524.

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: