DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2018-0327; Product Identifier 2018-CE-001-AD]
RIN 2120-AA64

Airworthiness Directives; Learjet, Inc. Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: We propose to adopt a new airworthiness directive (AD) for
certain Learjet, Inc. Models 28, 29, 31, 31A, 35, 35A, 36, 36A, 55,
55B, 55C, and 60 airplanes. This proposed AD was prompted by fatigue
cracks initiating in the flap support structure due to repetitive flap
loads, which has caused flap nose roller support bracket failure. This
proposed AD would require replacement of the flap nose roller fitting,
nose roller support bracket, and adjacent rib support structure with
more robust components. We are proposing this AD to address the unsafe
condition on these products.

DATES: We must receive comments on this proposed AD by June 22, 2018.

ADDRESSES: You may send comments, using the procedures found in 14 CFR
11.43 and 11.45, by any of the following methods:
Federal eRulemaking Portal: Go to http://www.regulations.gov. Follow the
instructions for submitting comments.
Fax: 202-493-2251.
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 Learjet,
Inc., One Learjet Way, Wichita, Kansas 67209; telephone: 316-946-2000;
email: ac.ict@aero.bombardier.com; internet: https://www.bombardier.com. You
may view this service information at the FAA,
Policy and Innovation Division, 901 Locust, Kansas City, Missouri
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 on the internet at http://www.regulations.gov
by searching for and locating Docket No. FAA-2018-
0327; 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, the regulatory evaluation, any comments received, and other
information. The street address for Docket Operations (phone: 800-647-
5527) is listed above. Comments will be available in the AD docket
shortly after receipt.

FOR FURTHER INFORMATION CONTACT: Tara Shawn, Aerospace Engineer,
Wichita ACO Branch, 1801 Airport Road, Room 100, Wichita, Kansas 67209;
telephone: (316) 946-4141; fax: (316) 946-4107; email:
tara.shawn@faa.gov or Wichita-COS@faa.gov.

SUPPLEMENTARY INFORMATION:

Comments Invited

We invite 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-2018-0327;
Product Identifier 2018-CE-001-AD'' at the beginning of your comments.
We specifically invite comments on the overall regulatory, economic,
environmental, and energy aspects of this NPRM. We will consider all
comments received by the closing date and may amend this NPRM because
of those comments.

We will post all comments we receive, without change, to
http://www.regulations.gov, including any personal information you provide. We
will also post a report summarizing each substantive verbal contact we
receive about this NPRM.

Discussion

We received a report of skewed flap and aileron binding due to
fatigue cracks in the flap support structure caused by repetitive flap
loads on a Learjet, Inc. Model 31A. As of June 2017, cracks in the flap
support structure were reported (due to Alert Service Bulletins
published in March 2017) on Models 31, 31A, 35A, 55, and 60 airplanes.
Repetitive flap loads occur on all models identified by this proposed
AD. Failure of the flap nose roller support bracket allows skewed flap
and aileron binding, which can cause loss of roll control on approach.
This condition, if not addressed, could result in loss of control.

Although there have been no reports of cracks on the Models 28, 29,
35, 36, 36A, 55B, and 55C airplanes, these airplanes do incorporate the
same design flap support structure.

Related Service Information Under 1 CFR Part 51

We reviewed Bombardier Learjet 28/29 Service Bulletin (SB) 28/29-
27-31 Recommended, dated September 11, 2017; Bombardier Learjet 31 SB
31-27-35 Recommended, dated September 11, 2017; Bombardier Learjet 35/
36 SB 35/36 -27-50 Recommended, dated September 11, 2017; Bombardier
Learjet 55 SB 55-27-41 Recommended, dated September 11, 2017; and
Bombardier Learjet 60 SB 60-27-39 Recommended, Revision 1, dated
January 15, 2018. For the applicable models, the service information
describes procedures for replacement of the flap nose roller fitting,
nose roller support bracket, and adjacent rib support structure with
improved components. The service information also contains instructions
to ensure correct flap alignment. 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.

FAA's Determination

We are proposing this AD because we evaluated all the relevant
information and determined the unsafe condition described previously is
likely to exist or develop in other products of the same type design.

Proposed AD Requirements

This proposed AD would require accomplishing the actions specified
in the service information described previously.

Differences Between This Proposed AD and the Service Information

The published service information does not list Models 31A, 35A,
36A, 55B, or 55C as affected models. However, the serial numbers in the
service information does reflect these models. The serial numbers in
the service information (except for Models 28/29) does not start with
-001, but the effectivity in this AD starts with -001 for all models.
The service information for all models also specifies to submit a
compliance response form to the manufacturer; however, this AD does not
require that action.

Costs of Compliance

We estimate that this proposed AD affects 706 airplanes of U.S.
registry.

We estimate the following costs to comply with this proposed AD:

Estimated Costs

* Parts cost is an average of the composite costs for replacement of all of the kits per airplane. Not all airplanes will need all kits, as credit is allowed for some previous installations.

Individual Parts Cost *

* Parts required for replacement may vary for different models and
different airplanes.

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.

We are 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.

This AD is issued in accordance with authority delegated by the
Executive Director, Aircraft Certification Service, as authorized by
FAA Order 8000.51C. In accordance with that order, issuance of ADs is
normally a function of the Compliance and Airworthiness Division, but
during this transition period, the Executive Director has delegated the
authority to issue ADs applicable to small airplanes, gliders,
balloons, airships, domestic business jet transport airplanes, and
associated appliances to the Director of the Policy and Innovation
Division.

Regulatory Findings

We 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) Is not a "significant rule'' under the DOT Regulatory Policies
and Procedures (44 FR 11034, February 26, 1979),

(3) Will not affect intrastate aviation in Alaska, and

(4) 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 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 adding the following new airworthiness
directive (AD):