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Federal Register / Vol. 86, No. 154 / Friday, August 13, 2021 / Proposed Rules searching for and locating Docket No.
FAA20210660; 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 9464135; email:
james.galstad@faa.gov or Wichita-COS@
faa.gov; or Thomas Teplik, Aviation Safety Engineer, Wichita ACO Branch, FAA, 1801 S Airport Road, Wichita, KS
67209; phone: 316 9464196; email:
thomas.teplik@faa.gov or Wichita-COS@
faa.gov.
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.
FAA20210660; Project Identifier AD
202100398T 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.

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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

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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.
FAAs 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
7301, Revision 1, Bombardier Learjet 45 SB 45732, Revision 1, Bombardier Learjet 70 SB 707301, Revision 1, and Bombardier Learjet 75 SB 757301, Revision 2, all dated January 9, 2017.
This service information specifies
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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 45732, Revision 1, dated January 9, 2017, begins with serial number 45005. This proposed AD
would also apply to airplane serial numbers 45002 through 45004
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:

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