# AD 2000-08-53: Main Rotor System - Type: Airworthiness directive - Status: Historical - Products: AST UH-1F, HH-1K, TH-1F, TH-1L, UH-1B, UH-1E, UH-1F, UH-1H, UH-1L, UH-1P, UH-1B, UH-1B and 23 more - Issued: April 26, 2000 - Supersedes: [AD 89-17-03](https://openairdocs.org/ad/89-17-03) - Superseded by: [AD 2000-22-51](https://openairdocs.org/ad/2000-22-51) - Product type: Aircraft, Rotorcraft - Docket: 2000-SW-08-AD - Registered aircraft: 39 may be affected, by airframe or engine model (OpenAirDocs) - FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/EF8A1AB797C8C26986256CCB0077561F.0001 - DRS record last changed: August 7, 2025 - Page: https://openairdocs.org/ad/2000-08-53 ## The airworthiness directive 2000-08-53 FIREFLY AVIATION HELICOPTER SERVICES (PREVIOUSLY ERICKSON AIR CRANE CO.); GARLICK HELICOPTERS, INC.; HAWKINS AND POWERS AVIATION, INC.; INTERNATIONAL HELICOPTERS, INC.; TAMARACK HELICOPTERS, INC. (PREVIOUSLY RANGER HELICOPTER SERVICES, INC.); ROBINSON AIR CRANE, INC.; WILLIAMS HELICOPTER CORPORATION (PREVIOUSLY SCOTT PAPER CO.); SMITH HELICOPTERS; SOUTHERN HELICOPTER, INC.; SOUTHWEST FLORIDA AVIATION; UTAH STATE UNIVERSITY; WESTERN INTERNATIONAL AVIATION, INC.; and U.S. HELICOPTER, INC: Docket No. 2000-SW-08-AD. Supersedes AD 89-17-03, Amendment 39-6251, Docket No. 88-ASW-33. Applicability: Bell Helicopter Textron Inc.-manufactured Model HH-1K, TH-1F, TH-1L, UH-1A, UH-1B, UH-1E, UH-1F, UH-1H, UH-1L, and UH-1P; and Southwest Florida Aviation SW204, SW204HP, SW205, and SW205A-1 helicopters, certificated in any category. NOTE 1: This AD applies to each helicopter identified in the preceding applicability provision, regardless of whether it has been otherwise modified, altered, or repaired in the area subject to the requirements of this AD. For helicopters that have been modified, altered, or repaired so that the performance of the requirements of this AD is affected, the owner/operator must request approval for an alternative method of compliance in accordance with paragraph (d) of this AD. The request should include an assessment of the effect of the modification, alteration, or repair on the unsafe condition addressed by this AD; and if the unsafe condition has not been eliminated, the request should include specific proposed actions to address it. Compliance: Required as indicated, unless previously accomplished. To prevent fatigue failure of the main rotor mast assembly (mast) or main rotor trunnion assembly (trunnion), separation of the main rotor system, and subsequent loss of control of the helicopter, accomplish the following: (a) For the main rotor mast assembly, part number (P/N) 204-011-450-001, -005, -007, -105,or -109: NOTE 2: The next higher assembly level for the affected P/N's are the 204-040-366 mast assemblies. Check the aircraft records for the appropriate P/N and assembly level. (1) Create a component history card or equivalent record for the mast within 10 hours time-in-service (TIS). (2) Determine and record the revised hours TIS to-date as follows: (i) Review the component history card or equivalent record for the mast and determine the hours TIS for each of the usage type categories (1) through (6) specified in Figure 1. Figure 1 (ii) Multiply the hours TIS for each of the different usage type categories by the flight hour factors specified in Figure 2. Add the factored flight hours in column B to determine the total factored flight hours to-date. (iii) Record the total factored flight hours on the component history card or equivalent record and use as the revised hours TIS for the mast. (3) Determine and record the accumulated retirement index number (RIN) to-date as follows: (i) Multiply the revised hours TIS determined in accordance with paragraph (a)(2) of this AD by the RIN conversion factor specified in Figure 2 to establish the baseline accumulated RIN for the mast. Figure 2 (ii) Record the RIN on the component history card or equivalent record and use as the accumulated RIN for the mast. (4) Before further flight, remove from service any mast, P/N 204-011-450-001 or -005, that has 6,000 or more revised hours TIS or 265,000 or more RIN. (5) Before further fight, remove from service any mast, P/N 204-011-450-007, -105, or -109, that has 15,000 or more revised hours TIS or 265,000 or more RIN. (6) Inspect the upper and lower snap ring grooves in the damper clamp splined area of mast, P/N 204-011-450-001, -005, -007, -105, or -109, for a minimum radius of 0.020 inches around the entire circumference (See Figures 3 and 4), using a 100x or higher magnification, according to the following schedule: NOTE 3: The mast serial number (S/N) may include the prefix NFS or N9. (i) S/N 23002 and prior, with less than 100,000 RIN, before 100,000 RIN. (ii) S/N 23002 and prior, with 100,000 or more RIN, within 10 hours TIS or 500 RIN, whichever occurs first. (iii) S/N 23003 through 36752, with less than 170,000 RIN, before 170,000 RIN. (iv) S/N 23003 through 36752, with 170,000 or more RIN, within 10 hours TIS or 500 RIN, whichever occurs first. (7) If any snap ring groove radius is less than 0.020 inches, replace the mast with an airworthy mast before accumulating 100,000 RIN or before further flight if the RIN equals or exceeds 100,000. (8) Inspect the upper and lower snap ring grooves of the mast, P/N 204-011-450-001, -005, -007, -105 or -109, for a burr (See Figures 3 through 5), using a 200x or higher magnification, according to the following schedule: (i) S/N 23002 and prior, with less than 100,000 RIN, before 100,000RIN. (ii) S/N 23002 and prior, with 100,000 or more RIN, within 10 hours TIS or 500 RIN, whichever occurs first. (iii) S/N 23003 through 36752, with less than 170,000 RIN, before 170,000 RIN. (iv) S/N 23003 through 36752, with 170,000 or more RIN, within 10 hours TIS or 500 RIN, whichever occurs first. (9) If a burr is found in any snap ring groove radius, replace the mast with an airworthy mast before accumulating 170,000 RIN or before further flight if the RIN equals or exceeds 170,000. Figure 3 Main Rotor Mast Figure 4 Snap Ring Groove/Spline Intersection Cutaway View Looking Down From Inside Snap Ring Groove Typical Burrs at Snap Ring Groove / Spline Intersection Burrs to be Inspected at 200x Minimum Magnification Figure 5 Typical Burr at Snap Ring Groove (10) Thereafter, calculate the accumulated RIN for the mast, P/N 204-011-450-001, -005, -007, -105, or -109, for all future torque events. Increasethe accumulated RIN count on the component history card or equivalent record using the RIN values specified in Figure 2 for each takeoff and external load lift. (11) After accomplishing the requirements of paragraphs (a)(1) and (a)(2) continue to count mast hours TIS. Count 10 hours TIS for each hour TIS that the helicopter is operated with a hub spring installed. (12) For the mast, P/N 204-011-450-001 or -005, this AD establishes a retirement life of 6,000 hours TIS or 265,000 RIN, whichever occurs first. (13) For the mast, P/N 204-011-450-007, -105, or -109, this AD establishes a retirement life of 15,000 hours TIS or 265,000 RIN, whichever occurs first. (b) Within 10 days after completing the inspections required by this AD, complete the AD compliance inspection report form, Appendix 1, with the requested information, and send it to the attention of the Manager, Rotorcraft Certification Office, Federal Aviation Administration, Fort Worth, Texas, 76193-0170,USA. Reporting requirements have been approved by the Office of Management and Budget and assigned OMB control number 2120-0056. (c) For the main rotor trunnion assembly, P/N 204-011-105-001: (1) Remove any trunnion with 14,900 or more hours TIS from service within the next 100 hours TIS. If the TIS cannot be determined, enter 900 hours for each year from the date the trunnion was installed. (2) Remove any trunnion with less than 14,900 hours TIS from service at or before 15,000 hours TIS. If the TIS cannot be determined, enter 900 hours for each year from the date the trunnion was installed. NOTE 4: The intent of paragraph (c) is to continue the requirements of AD 89-17-03 for the trunnion. (d) An alternative method of compliance or adjustment of the compliance time that provides an acceptable level of safety may be used if approved by the Manager, Rotorcraft Certification Office, Rotorcraft Directorate, FAA. Operators shall submit their requests through an FAA Principal Maintenance Inspector, who may concur or comment and then send it to the Manager, Rotorcraft Certification Office. NOTE 5: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Rotorcraft Certification Office. (e) Special flight permits may be issued in accordance with sections 21.197 and 21.199 of the Federal Aviation Regulations (14 CFR 21.197 and 21.199) to operate the helicopter to a location where the requirements of this AD can be accomplished. (f) Emergency AD 2000-08-53, issued April 26, 2000, becomes effective upon receipt. APPENDIX 1 AD COMPLIANCE INSPECTION REPORT FORM P/N 204-011-450-001/-005/-007/-105/-109 MAIN ROTOR MAST Complete the following information and mail or fax this form to: Manager, Rotorcraft Certification Office Federal Aviation Administration Fort Worth, Texas, 76193-0170, USA Fax: 817-222-5783 Operator Name:Aircraft Registration No.: Helicopter Model: Helicopter S/N: Mast P/N: Mast S/N: Mast RIN: Mast Total TIS: Inspection Results: 1. Were any radii during inspection of this mast determined to be less than 0.020 inches? If yes, what was the dimension measured? 2. Was a burr found in the inspected snap ring grooves? 3. Who performed this inspection? 4. Provide any other comments: ## Rule preamble ### Supplementary information This superseding Emergency Airworthiness Directive (AD) is prompted by an accident involving a BHTI Model 212 helicopter following in-flight separation of the main rotor system. The post-accident investigation revealed that the cause of the separation of the main rotor system was fatigue failure in the damper clamp splined area of the main rotor mast (mast), part number (P/N) 204-011-450-007. Also, operators have reported at least five other failures in the damper clamp splined area of masts, P/N 204-011-450-001, -007 and -105, in either the upper or lower snap ring grooves. The same main rotor system masts, or similar type designs, are used in some former military H-1 series helicopters. Metallurgical examination of the four most recently failed masts revealed that they all had snap ring groove radii smaller than the 0.020-inch minimum allowable dimension specified in the helicopter manufacturer's design drawing and some had burrs in the radius of the snap ring grooves. This condition, if not corrected, could result in fatigue failure of a mast, separation of the main rotor system, and subsequent loss of control of the helicopter. The FAA issued Final Rule AD 89-17-03 on June 14, 1989 (54 FR 31935, August 3, 1989), which established a mandatory fatigue retirement life on certain masts and trunnions. That action was prompted by results of the manufacturer's fatigue stress tests and fatigue analysis of the mast and trunnion under ground-air-ground and repeated heavy lift loading conditions. The FAA concluded from the tests and analysis that these components could no longer be operated with an unlimited service life and must be removed after a specified time in service. Since the issuance of that AD, several more fatigue failures have occurred. An accident involving a Model 205A-1 helicopter, in which a mast failure caused separation of the main rotor from the helicopter, prompted action which required converting accumulated factored flight hours toa baseline accumulated Retirement Index Number (RIN) count, establishing a system for tracking increases to the accumulated RIN, and establishing a maximum allowable RIN for certain masts. Analysis and fatigue testing conducted by the manufacturer confirmed that the remaining lives of the masts are more accurately assessed by monitoring the number of torque events (takeoffs or external load lifts) and flight hours incurred by the helicopter rather than monitoring only flight hours. Since an unsafe condition exists with similar masts as installed on former military helicopters of similar type designs, the FAA has determined that similar procedures and limitations need to be imposed on the restricted category helicopters. A one-time inspection is also mandated with a reduction in the maximum allowable RIN count for those masts with any burr or inadequate radius in the snap ring groove area that can cause a premature fatigue failure. Flight hour adjustments are also incorporated intothis emergency AD to account for the ten-fold reduction in life for any hours operated with a hub spring installed. The requirements of AD 89-17-03, pertaining to the trunnion, P/N 204-011-105-001, are continued and unchanged in this emergency AD. This emergency AD is being issued to correct an unsafe condition that is likely to exist or develop on BHTI-manufactured military Model HH-1K, TH-1F, TH-1L, UH-1A, UH-1B, UH-1E, UH-1F, UH-1H, UH-1L, and UH-1P; and Southwest Florida Aviation SW204, SW204HP, SW205, and SW205A-1 helicopters. For the mast, this emergency AD requires the following: * Creating a component history card or equivalent record; * Determining the accumulated factored hours TIS; * Establishing a baseline accumulated RIN count; * Establishing a RIN counting system for tracking increases to the accumulated RIN; * Accomplishing a one-time special inspection for burrs and inadequate radii in the snap ring groove areas; and * Establishing the hours TIS andRIN retirement lives for the masts. For the trunnion, this emergency AD continues the requirements of AD 89-17-03. This rule is issued under 49 U.S.C. Section 44701 pursuant to the authority delegated to me by the Administrator and is effective immediately upon receipt of this emergency AD. ## Affected data sheets (5) (OpenAirDocs) The type certificate data sheets whose models the AD names. - [TCDS H6SO](https://openairdocs.org/tcds/H6SO): Southwest Florida Aviation International; names 4 of 4 models: SW204HP (UH-1B), SW205 (UH-1H), SW204 (UH-1B), SW205A-1 - [TCDS H7SO](https://openairdocs.org/tcds/H7SO): Overseas Aircraft Support Inc.; names 3 of 5 models: TH-1L, UH-1L, UH-1E - [TCDS R00008AT](https://openairdocs.org/tcds/R00008AT): Robinson Air Crane Inc.; names 2 of 3 models: TH-1F, UH-1P - [TCDS H3SO](https://openairdocs.org/tcds/H3SO): Richards Heavylift Helo Inc.; names 1 of 4 models: UH-1A - [TCDS H5NM](https://openairdocs.org/tcds/H5NM): Midwest Aerospace TC LLC; names 1 of 4 models: HH-1K ## 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: 39 (39 by airframe model, 0 by engine model) - Makers: Southwest Florida 11, Williams Helicopter 7, Northwest Rotorcraft 6, Arrow Falcon Exporters 2, Garlick Helicopters 2, Hawkins & Powers 2, Richards Heavylift Helo 2, Rotorcraft Development 2, Western International Avia 2, Bell-Sw Florida Avn 1 Models with the most aircraft: - [Northwest Rotorcraft UH-1H](https://openairdocs.org/model/northwest-rotorcraft-uh-1h): 6 aircraft (airframe model) - [Williams Helicopter UH-1H](https://openairdocs.org/model/williams-helicopter-uh-1h): 6 aircraft (airframe model) - [Southwest Florida SW205](https://openairdocs.org/model/southwest-florida-sw205): 5 aircraft (airframe model) - [Southwest Florida UH-1H](https://openairdocs.org/model/southwest-florida-uh-1h): 3 aircraft (airframe model) - [Southwest Florida SW204](https://openairdocs.org/model/southwest-florida-sw204): 2 aircraft (airframe model) - [Richards Heavylift Helo UH-1H](https://openairdocs.org/model/richards-heavylift-helo-uh-1h): 2 aircraft (airframe model) - [Hawkins & Powers UH-1B](https://openairdocs.org/model/hawkins-powers-uh-1b): 2 aircraft (airframe model) - [Arrow Falcon Exporters UH-1H](https://openairdocs.org/model/arrow-falcon-exporters-uh-1h): 2 aircraft (airframe model) - [Garlick Helicopters HH-1K](https://openairdocs.org/model/garlick-helicopters-hh-1k): 2 aircraft (airframe model) - [Rotorcraft Development UH-1H](https://openairdocs.org/model/rotorcraft-development-uh-1h): 2 aircraft (airframe model) - [Western International Avia UH-1H](https://openairdocs.org/model/western-international-avia-uh-1h): 2 aircraft (airframe model) - [Bell-Sw Florida Avn UH-1B](https://openairdocs.org/model/bell-sw-florida-avn-uh-1b): 1 aircraft (airframe model) - [Southwest Florida SW204HP](https://openairdocs.org/model/southwest-florida-sw204hp): 1 aircraft (airframe model) - [Precision Helicopters UH-1H](https://openairdocs.org/model/precision-helicopters-uh-1h): 1 aircraft (airframe model) - [Williams Helicopter UH-1B](https://openairdocs.org/model/williams-helicopter-uh-1b): 1 aircraft (airframe model) - [Williams Helicopter Corp/Oas UH-1E](https://openairdocs.org/model/williams-helicopter-corp-oas-uh-1e): 1 aircraft (airframe model) All 16 models: https://openairdocs.org/ad/2000-08-53/models.md Every aircraft: https://openairdocs.org/ad/2000-08-53/aircraft.md ## Related documents - [AD 89-17-03](https://openairdocs.org/ad/89-17-03) (historical): Main Rotor Masts · California Department of Forestry UH-1F, TH-1L, UH-1B and 18 more. Effective Sep 5, 1989. Replaced by this AD - [AD 2000-22-51](https://openairdocs.org/ad/2000-22-51) (historical): Main Rotor Mast or Trunnion · Arrow Falcon Exporters UH-1H, UH-1F, HH-1K and 33 more. Effective Dec 26, 2000. Supersedes this AD Its text cites no advisory circulars or STCs. --- 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.