# AD 2021-24-15: Tail Rotor Drive Shaft - Type: Airworthiness directive - Status: Current - Products: Bell Textron Canada 206L-1, 206L-3 and 206L-4 with STC SH2750NM - Effective: January 18, 2022 - Published: December 14, 2021, 86 FR 70966–70969 - Issued: November 19, 2021 - Issued as: Final rule - Superseded by: Nothing supersedes this AD - Product type: Aircraft, Rotorcraft - Amendment: 39-21836 - Docket: FAA-2021-0830 (https://www.regulations.gov/docket/FAA-2021-0830) - Project: AD-2020-00257-R - Registered aircraft: 537 may be affected, by airframe or engine model (OpenAirDocs) - Official PDF: https://openairdocs.org/files/sha256/71/e5/71e5f94d9d6eaf1652966a91fab206b1dba0e68f16d2b1ac641a1f86329a84c4 (from https://www.govinfo.gov/content/pkg/FR-2021-12-14/pdf/2021-27012.pdf) - Federal Register: https://www.federalregister.gov/documents/2021/12/14/2021-27012/airworthiness-directives-bell-textron-canada-limited-helicopters - FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/FR-ADFRAWD-2021-27012-0000000000.0001 - DRS record last changed: November 21, 2025 - Page: https://openairdocs.org/ad/2021-24-15 ## Summary The FAA is adopting a new airworthiness directive (AD) for Bell Textron Canada Limited Model 206L-1, 206L-3, and 206L-4 helicopters with certain Air Comm Corporation air conditioning systems installed. This AD was prompted by reports of damage to the drive ring spline teeth and the mating spline teeth. This AD requires visually inspecting the drive ring spline teeth and the mating area spline teeth on the oil cooler blower shaft for signs of deformation and fretting and depending on the results of the inspection, removing certain parts from service. This AD also requires reinstalling certain parts, applying torque, and aligning certain bolt holes. The FAA is issuing this AD to address the unsafe condition on these products. ## The airworthiness directive 1. The authority citation for part 39 continues to read as follows: 2. The FAA amends § 39.13 by adding the following new airworthiness directive: 2021-24-15 Bell Textron Canada Limited: Amendment 39-21836; Docket No. FAA-2021-0830; Project Identifier AD-2020-00257-R. ### (a) Effective Date This airworthiness directive (AD) is effective January 18, 2022. ### (b) Affected ADs None. ### (c) Applicability This AD applies to the Bell Textron Canada Limited helicopters identified in paragraphs (c)(1) and (2) of this AD: (1) Model 206L-1 and Model 206L-3 helicopters, certificated in any category, with Bell Model 206L1/L3 Service Instruction for Increased Gross Weight Upgrade Kit BHT-206-SI-2052, Revision 1, dated October 14, 2010, installed and that are equipped with one of the following Air Comm Corporation Supplemental Type Certificate (STC) SH2750NM air conditioning systems part number (P/N) 206EC-204-1, 206EC-204-2, 206EC-208-1, 206EC-208-2, 206EC-210-1, 206EC-210-2, 206EC-210-3, 206EC-212-3, or 206EC-212-4; and Note 1 to paragraph (c)(1) of this AD: Helicopters with a 206L-1+ designation are Model 206L-1 helicopters and helicopters with a 206L-3+ designation are Model 206L-3 helicopters. (2) Model 206 L-4 helicopters, certificated in any category, and that are equipped with one of the following Air Comm Corporation STC SH2750NM air conditioning systems P/N 206EC-204-1, 206EC-204-2, 206EC-208-1, 206EC-208-2, 206EC-210-1, 206EC-210-2, 206EC-210-3, 206EC-212-3, or 206EC-212-4. ### (d) Subject Joint Aircraft Service Component (JASC) Code: 6510, Tail Rotor Drive Shaft. ### (e) Unsafe Condition This AD was prompted by reports of deformation or fretting of the spline teeth on the air conditioning system drive ring and on the oil cooler blower shaft. The FAA is issuing this AD to detect deformation and fretting. The unsafe condition, if not addressed, could result in a failure of the oil cooler blower shaft, which could lead to loss of tail rotor authority and subsequent loss of helicopter control. ### (f) Compliance Comply with this AD within the compliance times specified, unless already done. ### (g) Required Actions Within 300 hours time-in-service (TIS) after the effective date of this AD, and thereafter at intervals not to exceed 300 hours TIS: (1) Gain access to the drive ring spline teeth and the mating area spline teeth on the oil cooler blower shaft by removing the tail rotor drive system's forward short shaft and spline adaptor, and the air conditioner system's drive ring. Refer to Figure 1 of ACC Air Comm Corporation Service Bulletin SB 206EC-091119, Rev B, dated May 26, 2021 for a depiction of each component's location. (2) Visually inspect the drive ring spline teeth and the mating area spline teeth on the oil cooler blower shaft for deformation and fretting. (i) If there is deformation or fretting on the drive ring spline teeth, before further flight, remove the drive ring from service and replace it with an airworthy part. (ii) If there is deformation or fretting on the mating area spline teeth of the oil cooler blower shaft, before further flight, remove the oil cooler blower assembly from service and replace with an airworthy part. (3) Reinstall the drive ring, spline adapter, and the forward short shaft. If the compressor drive pulley was removed, torque the drive pulley to 200-300 in-lbs, increasing torque in this range to align the four threaded holes with the through holes in the drive ring. Do not back-off torque to align the bolt holes. ### (h) Special Flight Permits Special flight permits are prohibited. ### (i) Alternative Methods of Compliance (AMOCs) (1) The Manager, Denver ACO, 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 Denver ACO, send it to the attention of the person identified in paragraph (j)(1) of this AD. Information may be emailed to: 9-Denver-Aircraft-Cert@faa.gov. (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. ### (j) Related Information (1) For more information about this AD, contact Matthew Bryant, Aerospace Engineer, Denver ACO Branch, FAA, 26805 East 68th Avenue, Denver, CO 80249; telephone (303) 342-1092; email 9-Denver-Aircraft-Cert@faa.gov. (2) Service information identified in this AD, is available at the contact information specified in paragraphs (k)(3) and (4) of this AD. ### (k) Material Incorporated by Reference (1) The Director of the Federal Register approved the incorporation by reference of the service information listed in this paragraph under 5 U.S.C. 552(a) and 1 CFR part 51. (2) You must use this service information as applicable to do the actions required by this AD, unless the AD specifies otherwise. (i) ACC Air Comm Corporation Service Bulletin SB 206EC-091119, Rev B, dated May 26, 2021. (ii) [Reserved] (3) For service information identified in this AD, contact Air Comm Corporation, 1575 W 124th Ave. #210, Westminster, CO 80234; telephone: (303) 440-4075; email service@aircommcorp.com. (4) You may view this service information at the FAA, Office of the Regional Counsel, Southwest Region, 10101 Hillwood Pkwy., Room 6N-321, Fort Worth, TX 76177. For information on the availability of this material at the FAA, call (817) 222-5110. (5) You may view this service information that is incorporated by reference at the National Archives and Records Administration (NARA). For information on the availability of this material at NARA, email: fr.inspection@nara.gov, or go to: https://www.archives.gov/federal-register/cfr/ibr-locations.html. ## Rule preamble ### Dates This AD is effective January 18, 2022. The Director of the Federal Register approved the incorporation by reference of a certain document listed in this AD as of January 18, 2022. ### Addresses For service information identified in this final rule, contact Air Comm Corporation, 1575 Westminster, CO 80234; telephone (303) 440-4075; or at https://www.aircommcorp.com. You may view the referenced service information at the FAA, Office of the Regional Counsel, Southwest Region, 10101 Hillwood Pkwy., Room 6N-321, Fort Worth, TX 76177. For information on the availability of this material at the FAA, call (817) 222-5110. It is also available at https://www.regulations.gov by searching for and locating Docket No. FAA-2021-0830. ### For further information contact Matthew Bryant, Aerospace Engineer, Denver ACO Branch, FAA, 26805 East 68th Avenue, Denver, CO 80249; telephone (303) 342-1080; email 9-Denver-Aircraft-Cert@faa.gov. ### Background The FAA issued a notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 by adding an AD that would apply to Bell Textron Canada Limited Model 206L-1, Model 206L-3, and Model 206L-4 helicopters with certain Air Comm Corporation air conditioning systems installed. The NPRM published in the Federal Register on September 24, 2021 (86 FR 53015). In the NPRM, the FAA proposed to require within 300 hours time-in-service (TIS), and thereafter at intervals not to exceed 300 hours TIS, gaining access to the drive ring spline teeth and the mating area spline teeth on the oil cooler blower shaft, repetitively inspecting the drive ring spline teeth and the mating spline teeth on the tail rotor drive's oil cooler blower shaft for deformation and fretting, and depending on the results of each inspection, removing certain parts from service before further flight. The NPRM also proposed to require reinstalling certain parts, and if required, reinstalling the drive pulley by torqueing and aligning the drive pulley bolt holes. The FAA issued Special Airworthiness Information Bulletin SW-19-05 on April 4, 2019 (SAIB SW-19-05), to alert owners and operators of Bell Textron Canada Limited Model 206L-1, 206L-3, and 206L-4 helicopters with Air Comm Corporation's Supplemental Type Certificate (STC) SH2750NM installed. SAIB SW-19-05 was prompted by reports of the air conditioner pulley's locking system, which is installed on the oil cooler drive shaft's splined quill, causing excessive spline tooth wear to the drive ring spline teeth and the mating spline teeth on the oil cooler blower shaft. SAIB SW-19-05 recommends following the inspection instructions of certain Air Comm Corporation service information and routinely inspecting the air conditioner pulley lock ring. At the time SAIB SW-19-05 was issued, the airworthiness concern was not determined to be an unsafe condition that would warrant AD action under 14 CFR part 39. However, subsequent investigations were not able to determine whether the limited damaged observed on several oil cooler blower shafts would remain localized or progress to a point where the shaft is no longer safe for continued use. The FAA also later determined that operators may have difficulty aligning the air conditioning system's drive ring holes with the air conditioning condenser drive pulley without leaving the condenser drive pulley under-torqued. This condition, if not addressed, could result in a failure of the oil cooler blower shaft, which could lead to loss of tail rotor authority and subsequent loss of helicopter control. Accordingly, the FAA is issuing this AD for Bell Textron Canada Limited Model 206L-1 and 206L-3 helicopters with Bell Model 206L1/L3 Service Instruction for Increased Gross Weight Upgrade Kit BHT-206-SI-2052, Revision 1, dated October 14, 2010, installed and Bell Model 206L-4 helicopters equipped with one of the following Air Comm Corporation STC SH2750NM air conditioning systems part number; 206EC-204-1, 206EC-204-2, 206EC-208-1, 206EC-208-2, 206EC-210-1, 206EC-210-2, 206EC-210-3, 206EC-212-3 or 206EC-212-4. Helicopters with a 206L-1+ designation are Model 206L-1 helicopters and helicopters with a 206L-3+ designation are Model 206L-3 helicopters. ### Comments The FAA received no comments on the NPRM or on the determination of the costs. ### Conclusion The FAA reviewed the relevant data and determined that air safety requires adopting this AD as proposed except for minor editorial changes. Accordingly, the FAA is issuing this AD to address the unsafe condition on these helicopters. ### Related Service Information Under 1 CFR Part 51 The FAA reviewed ACC Air Comm Corporation Service Bulletin SB 206EC-091119, Rev B, dated May 26, 2021 (SB 206EC-091119 Rev B), which specifies procedures for visually inspecting the drive ring spline teeth and the mating spline teeth on the tail rotor drive's oil cooler blower shaft for deformation or fretting. 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. ### Differences Between This AD and the Service Bulletin SB 206EC-091119 Rev B requires inspecting the air conditioning compressor drive belt tension and the general condition of the drive belt, drive pulley, and surrounding components, whereas this AD does not. SB 206EC-091119 Rev B requires reporting any deformation or fretting to Air Comm Corporation Service Department, whereas this AD does not. SB 206EC-091119 Rev B provides an option to deactivate the air conditioning system if deformation or fretting is found on the drive ring or the oil cooler blower shaft assembly, whereas this AD requires removing these parts from service instead. ### Costs of Compliance The FAA estimates that this AD affects up to 100 helicopters of U.S. Registry. Labor rates are estimated at $85 per work-hour. Based on these numbers, the FAA estimates the following costs to comply with this AD. Removing the tail rotor drive system's forward short shaft, spline adaptor, and drive ring and visually inspecting the drive ring spline teeth and the mating area spline teeth take about 1 work-hour for an estimated cost of $85 per helicopter and $8,500 for the U.S. fleet per inspection cycle. Replacing the drive ring takes about 3 work-hours and parts cost about $300 for an estimated cost of $555 per replacement. Replacing the oil cooler blower assembly takes about 3 work-hours and parts cost about $2,720 for an estimated cost of $2,975 per replacement. Aligning each bolt hole and re-torqueing the drive pulley take about 0.5 work-hours for an estimated cost of $43 per helicopter. ### 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. ### The Amendment Accordingly, under the authority delegated to me by the Administrator, the FAA amends 14 CFR part 39 as follows: ## Affected data sheets (1) (OpenAirDocs) The type certificate data sheets whose models the AD names. - [TCDS H2SW](https://openairdocs.org/tcds/H2SW): Bell Textron Canada Limited; names 3 of 12 models: 206L-1, 206L-4, 206L-3 ## Registered aircraft it may apply to (OpenAirDocs) Matched by airframe and engine model; the AD's applicability may narrow it by serial number, part number or equipment. - Aircraft: 537 (537 by airframe model, 0 by engine model) - Makers: Bell 281, Bell Helicopter Textron 149, Bell Helicopter Textron Canada 107 Models with the most aircraft: - [Bell 206L-3](https://openairdocs.org/model/bell-206l-3): 159 aircraft (airframe model) - [Bell Helicopter Textron 206L-1](https://openairdocs.org/model/bell-helicopter-textron-206l-1): 149 aircraft (airframe model) - [Bell 206-L4](https://openairdocs.org/model/bell-206-l4): 122 aircraft (airframe model) - [Bell Helicopter Textron Canada 206L-4](https://openairdocs.org/model/bell-helicopter-textron-canada-206l-4): 103 aircraft (airframe model) - [Bell Helicopter Textron Canada 206L-3](https://openairdocs.org/model/bell-helicopter-textron-canada-206l-3): 4 aircraft (airframe model) All 5 models: https://openairdocs.org/ad/2021-24-15/models.md Every aircraft: https://openairdocs.org/ad/2021-24-15/aircraft.md ## Related documents - [Proposed rule FAA-2021-0830](https://openairdocs.org/proposed/FAA-2021-0830): Notice of proposed rulemaking (NPRM), published Sep 24, 2021 - [STC SH2750NM](https://openairdocs.org/stc/SH2750NM): Installation of a Freon type cabin air conditioning system with engine-driven compressor. Air Comm Corporation, Named in the applicability --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.