[Federal Register Volume 86, Number 154 (Friday, August 13, 2021)]
[Proposed Rules]
[Pages 44660-44663]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2021-17044]


-----------------------------------------------------------------------

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2021-0660; Project Identifier AD-2021-00398-T]
RIN 2120-AA64


Airworthiness Directives; Learjet Inc. Airplanes

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 Learjet Inc. Model 45 airplanes. This proposed AD was 
prompted by a report of a fuel leak due to a cracked fuel line between 
the engine fuel control and the engine fuel flow meter. This proposed 
AD would require replacing the existing fuel flow meter bracket 
assembly with a redesigned bracket assembly and reporting information 
to the FAA. 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 September 
27, 2021.

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 https://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, KS 67209; phone: (316) 946-2000; email: 
[email protected]; website: https://businessaircraft.bombardier.com/en/aircraft/Learjet.html. You may view 
this 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

[[Page 44661]]

searching for and locating Docket No. FAA-2021-0660; 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: James Galstad, Aviation Safety 
Engineer, Wichita ACO Branch, FAA, 1801 S Airport Road, Wichita, KS 
67209; phone: (316) 946-4135; email: [email protected] or [email protected]; or Thomas Teplik, Aviation Safety Engineer, Wichita ACO 
Branch, FAA, 1801 S Airport Road, Wichita, KS 67209; phone: (316) 946-
4196; email: [email protected] or [email protected].

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 ADDRESSES. Include ``Docket No. FAA-2021-0660; Project Identifier 
AD-2021-00398-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 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 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 James 
Galstad, Aviation Safety Engineer, or Thomas Teplik, Aviation Safety 
Engineer, Wichita ACO Branch, FAA, 1801 S Airport Road, Wichita, KS 
67209. 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 of a fuel leak due to a cracked fuel line 
between the engine fuel control and the engine fuel flow meter on a 
Learjet Model 45 (Learjet 45) airplane. There are four different Model 
45 configurations: Model 45 (Learjet 40), Model 45 (Learjet 45), Model 
45 (Learjet 70), and Model 45 (Learjet 75). They all are susceptible to 
cracked fuel lines with possible fuel leakage because the fuel flow 
meter bracket and fuel line is common to each model. Further analysis 
of the fleet of all the 45 models revealed similar failures in this 
area including the following: 16 fuel line failures, 2 instances of 
multiple inlet attaching bolts breaking, 9 leaking fuel controls, a 
broken gearbox strut, 4 cracked No. 6 bearing oil supply lines, and 7 
cracked engine oil tanks. The FAA evaluated the flammable fluid leaks 
and broken parts and determined that they may have resulted from 
vibration.
    Following the above report and analysis, Learjet designed a new 
engine fuel flow meter bracket and incorporated it during production. 
The unsafe condition, if not addressed, could result in an engine 
installation fire, which could progress to an uncontrolled fire and 
consequent loss of control of the airplane.

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.

Related Service Information Under 1 CFR Part 51

    The FAA reviewed Bombardier Learjet 40 Service Bulletin (SB) SB 40-
73-01, Revision 1, Bombardier Learjet 45 SB 45-73-2, Revision 1, 
Bombardier Learjet 70 SB 70-73-01, Revision 1, and Bombardier Learjet 
75 SB 75-73-01, Revision 2, all dated January 9, 2017. This service 
information specifies procedures for replacing the existing fuel flow 
meter bracket assembly with a redesigned bracket assembly with pad fuel 
flow meter that has an increased material thickness. These documents 
are distinct since they apply to different airplane models. 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 ADDRESSES.

Proposed AD Requirements in This NPRM

    This proposed AD would require accomplishing the actions specified 
in the service information already described, except as discussed under 
``Differences Between this Proposed AD and the Service Information.''

Differences Between This Proposed AD and the Service Information

    This proposed AD would require reporting certain maintenance 
information to the FAA, where the service information does not. The 
information provided in the reports would be related to contributing 
factors that the FAA found showed a correlation between the reported 
engine fan vibration levels and the cracking fuel line between engine 
fuel control and the engine fuel flow meter and a correlation between 
the cracking fuel line and a certain batch of fan disks. In addition, 
the FAA found that a contributing factor could be the susceptibility of 
the fuel flow meter bracket assembly and the susceptibility of the 
bracket assembly with pad fuel flow meter to the vibration induced. The 
requested reporting information would allow the FAA to determine 
whether further rulemaking action would be necessary to mitigate the 
unsafe condition.
    Also, the effectivity of Bombardier Learjet 45 SB 45-73-2, Revision 
1, dated January 9, 2017, begins with serial number 45-005. This 
proposed AD would also apply to airplane serial numbers 45-002 through 
45-004 because, although these three airplanes are not currently in 
service, they are subject to the unsafe condition. Thus, it is 
necessary to include them in the event they are returned to service.

Costs of Compliance

    The FAA estimates that this AD, if adopted as proposed, would 
affect 443 airplanes of U.S. registry.
    The FAA estimates the following costs to comply with this proposed 
AD:

[[Page 44662]]



                                                 Estimated Costs
----------------------------------------------------------------------------------------------------------------
                                                                                     Cost per      Cost on U.S.
             Action                    Labor cost              Parts cost             product        operators
----------------------------------------------------------------------------------------------------------------
Replacing the bracket assembly..  4.5 work-hours x     $3,895...................       $4,277.50   $1,894,932.50
                                   $85 per hour =
                                   $382.50.
Reporting and reviewing logbooks  9 work-hours x $85   Not Applicable...........             765         338,895
                                   per hour = $765.
----------------------------------------------------------------------------------------------------------------

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 current 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 9 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

    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 
tween 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:

Learjet Inc.: Docket No. FAA-2021-0660; Project Identifier AD-2021-
00398-T.

(a) Comments Due Date

    The FAA must receive comments on this airworthiness directive 
(AD) by September 27, 2021.

(b) Affected ADs

    None.

(c) Applicability

    This AD applies to Learjet Inc. Model 45 (Learjet 40), Model 45 
(Learjet 45), Model 45 (Learjet 70), and Model 45 (Learjet 75) 
airplanes, serial numbers 45-002 through 45-556 and 45-2001 through 
45-2146, certificated in any category.

(d) Subject

    Joint Aircraft System Component (JASC) Code 7100, Powerplant 
System.

(e) Unsafe Condition

    This AD was prompted by a report of a fuel leak due to a cracked 
fuel line between the engine fuel control and the engine fuel flow 
meter. The FAA is issuing this AD to prevent cracking and failures. 
The unsafe condition, if not addressed, could result in an engine 
installation fire, which could progress to an uncontrolled fire and 
consequent loss of control of the airplane.

(f) Compliance

    Comply with this AD within the compliance times specified, 
unless already done.

(g) Reporting Requirement

    Within 60 days after the effective date of this AD, report the 
following information, where available, to the Wichita ACO Branch 
via email at [email protected], [email protected], and 
[email protected]; or by mail to Wichita ACO Branch, Attn: James 
Galstad/Thomas Teplik, 1801 S Airport Road, Room 100, Wichita, KS 
67209.
    (1) Name of the owner; the address of the owner; name of the 
organization doing the actions required by this AD; the date the 
actions were completed; the name of the person submitting the 
report; the address, telephone number, and email of the person 
submitting the report.
    (2) The fan vibration levels that have been recorded in the 
airplane and engine maintenance records since November 1, 2019. 
Include the airplane and engine serial numbers.
    (3) The date of each vibration level recorded and the associated 
hours time-in-service for the airplane and each engine.
    (4) For each fan vibration level reported, include:
    (i) Whether molybdenum coating for the fan was applied per 
Temporary Revision 72-494, dated August 15, 2017 (or as subsequently 
incorporated into the engine's Inspection/Repair Manual TFE731 (ATA 
Number 72-IR-02).
    (ii) If molybdenum coating was applied using a different process 
than Temporary Revision 72-494, dated August 15, 2017 (or as 
subsequently incorporated into the engine's Inspection/Repair Manual 
TFE731 (ATA Number 72-IR-02), report the process by which the 
molybdenum coating was applied and the revision level of the 
document defining the application process for the molybdenum 
coating.

    Note 1 to paragraph (g)(4): Temporary Revision 72-494, dated 
August 15, 2017, specifies applying a dry film lubricant on the 
mating surfaces of the fan hub and the fan blades. The lubricating 
solid for this dry film lubricant is molybdenum disulfide, which is 
referred to in this AD as molybdenum coating.


[[Page 44663]]


    (5) For each fan vibration level reported, the fan hub serial 
number and hours time-in-service for this fan hub.
    (6) Installation date and service bulletin (SB) revision level 
for the installation of the bracket assembly with pad fuel flow 
meter and hose if installed before the effective date of this AD.
    (7) Any failures of the bracket assembly with pad fuel flow 
meter and hose installed in accordance with any SB listed in 
paragraph (h) or any prior revision of these SBs.
    (8) Installation date and SB revision level used for 
installation of the fuel control screws within the engine fuel 
control in accordance with Honeywell SB TFE731-73-5146
    (9) Any failures of fuel control screws after compliance with 
Honeywell SB TFE731-73-5146.

(h) Replacement

    Within 12 months after the effective date of this AD or 750 
hours time-in-service after the effective date of this AD, whichever 
occurs first, replace the engine fuel flow meter bracket in 
accordance with the Accomplishment Instructions, paragraphs 3.A 
through 3.C, of the following Bombardier SB applicable to your 
airplane model.
    (1) Bombardier Learjet 40 SB 40-73-01, Revision 1, dated January 
9, 2017.
    (2) Bombardier Learjet 45 SB 45-73-2 Revision 1, dated January 
9, 2017.
    (3) Bombardier Learjet 70 SB 70-73-01 Revision 1, dated January 
9, 2017.
    (4) Bombardier Learjet 75 SB 75-73-01, Revision 2, dated January 
9, 2017.

 (i) Credit for Previous Actions

    (1) This paragraph provides credit for the actions required by 
paragraph (h) of this AD, if those actions were performed before the 
effective date of this AD using Bombardier Learjet 40 SB 40-73-01, 
Basic Issue, Bombardier Learjet 45 Service Bulletin SB 45-73-2, 
Basic Issue, Bombardier Learjet 70 SB 70-73-01, Basic Issue, or 
Bombardier Learjet 75 SB 75-73-01, Basic Issue, all dated October 3, 
2016, or Bombardier Learjet 75 SB 75-73-01, Revision 1, dated 
October 10, 2016.
    (2) To take credit for any previous action, you must comply with 
paragraph (g) of this AD within 60 days after the effective date of 
this AD.

(j) Alternative Methods of Compliance (AMOCs)

    (1) The Manager, Wichita ACO 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 certification office, send it to the attention of the 
person identified in Related Information.
    (2) 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.

(k) Related Information

    (1) For more information about this AD, contact James Galstad, 
Aviation Safety Engineer, Wichita ACO Branch, FAA, 1801 S Airport 
Road, Wichita, KS 67209; phone: (316) 946-4135; email: 
[email protected] or [email protected]; or Thomas Teplik, 
Aviation Safety Engineer, Wichita ACO Branch, FAA, 1801 S Airport 
Road, Wichita, KS 67209; phone: (316) 946-4196; email: 
[email protected].
    (2) For service information identified in this AD, contact 
Learjet Inc., One Learjet Way, Wichita, KS, 67209; phone: (316) 946-
2000; email: [email protected]; 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.

    Issued on August 5, 2021.
Lance T. Gant,
Director, Compliance & Airworthiness Division, Aircraft Certification 
Service.
[FR Doc. 2021-17044 Filed 8-12-21; 8:45 am]
BILLING CODE 4910-13-P