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Federal Register / Vol. 86, No. 154 / Friday, August 13, 2021 / Proposed Rules Monday through Friday, except Federal holidays.
For service information identified in this NPRM, contact MD Helicopters, Inc., Attn: Customer Support Division, 4555 E McDowell Rd., Mail Stop M615, Mesa, AZ 852159734; telephone 800
3883378; fax 480 3466813; or at https www.mdhelicopters.com. You may view this service information at the FAA, Office of the Regional Counsel, Southwest Region, 10101 Hillwood Pkwy., Room 6N321, Fort Worth, TX
76177. For information on the availability of this material at the FAA, call 817 2225110.

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Examining the AD Docket You may examine the AD docket at https www.regulations.gov by searching for and locating Docket No.
FAA20210653; 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:
Payman Soltani, Aerospace Engineer, Airframe Section, Los Angeles ACO
Branch, Compliance & Airworthiness Division, FAA, 3960 Paramount Blvd., Lakewood, CA 90712; telephone 562
6275313; email payman.soltani@
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.
FAA20210653; Project Identifier AD
202100170R 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
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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 Payman Soltani, Aerospace Engineer, Airframe Section, Los Angeles ACO Branch, Compliance &
Airworthiness Division, FAA, 3960
Paramount Blvd., Lakewood, CA 90712;
telephone 562 6275313; email payman.soltani@faa.gov. 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 proposes to adopt a new AD
for MDHI Model 369D, 369E, 369F, 369FF, 369H, 369HE, 369HM, 369HS, 500N, and 600N helicopters. This proposed AD would require a one-time visual and recurring borescope inspections of the torque tube and depending on the results, removing the torque tube from service. This proposed AD was prompted by a report of a spiral crack in the torque tube that appears to have originated from a hole where the tail rotor torque tube control fitting attaches to the torque tube on a Model 369FF helicopter. This crack resulted in increased left pedal movement and subsequent reduced directional control pedal authority. Other model helicopters are affected due to design similarity. This condition, if not addressed, could result in failure of the torque tube, loss of tail rotor control, and subsequent loss of control of the helicopter.
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 these same type designs.
Related Service Information Under 1
CFR Part 51
The FAA reviewed MD Helicopters Service Bulletin SB369D229R2 for Model 369D helicopters, SB369E129R2
for Model 369E helicopters, SB369F

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119R2 for Model 369F and 369FF
helicopters, SB369H263R2 for Model 369H, 369HE, 369HM, and 369HS
helicopters, SB500N066R2 for Model 500N helicopters, and SB600N080R2
for Model 600N helicopters, each dated March 24, 2021 Revision 2. These service bulletins are co-published as one document. Revision 2 of this service information specifies procedures for a one-time visual inspection and recurring borescope inspections, completing a Service Operation Report, and returning a removed torque tube to an authorized service center or MDHI.
Other Related Service Information The FAA also reviewed MD
Helicopters Service Bulletin SB369H
263, SB369D229, SB369E129, SB369F119, SB500N066, and SB600N080, each dated January 30, 2020 initial issuance, and MD
Helicopters Service Bulletin SB369H
263R1, SB369D229R1, SB369E129R1, SB369F119R1, SB500N066R1, and SB600N080R1, each dated May, 15
2020 Revision 1. The initial issuance and Revision 1 of this service information specify the same procedures as Revision 2 of this service information, except Revision 1 clarified the torque value to apply to the nut and Revision 2 deletes Method 2 of the Accomplishment Instructions and adds a recurring 300-hour borescope inspection of the torque tube.
Proposed AD Requirements in This NPRM
This proposed AD would initially require visually inspecting the torque tube exterior using a flashlight and mirror and borescope inspecting the interface of the torque tube and bushing segments for a crack, elongation, and other damage, which may be indicated by any corrosion, pitting, crazing, dents, dings, displacement of material at the bolt hole edge, or fretting of the hole.
Thereafter, this proposed AD would require repeating the borescope inspection. If there is a crack, elongation, or other damage, this proposed AD would require removing the torque tube from service.
Differences Between This Proposed AD
and the Service Information For helicopters that have accumulated 600 or less total hours time-in-service TIS, Revision 2 of the service information specifies an initial compliance time of during the next 100hour inspection, whereas this proposed AD would require initial actions within 100 hours TIS after the effective date of this AD instead. For helicopters that have accumulated more than 600 total
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