# AD 73-20-03: Main Rotor Hub - Type: Airworthiness directive - Status: Current - Products: Hiller UH-12, UH-12A, UH-12B, UH-12C, UH-12D, UH-12E and UH-12E-L - Effective: October 30, 1973 - Superseded by: Nothing supersedes this AD - Product type: Aircraft, Rotorcraft - Amendment: 39-1724 - Registered aircraft: 222 may be affected, by airframe or engine model (OpenAirDocs) - FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/58FDAB5B350B2DFD86256A38005FF9A2.0001 - DRS record last changed: May 30, 2024 - Page: https://openairdocs.org/ad/73-20-03 ## The airworthiness directive 73-20-03 HILLER AVIATION: Amdt. 39-1724. Applies to Hiller Model UH-12, UH-12A, UH-12B, UH-12C, UH-12D, and UH-12E Helicopters certificated in all categories. Compliance required within the next 5 hours time in service after the effective date of this AD, unless already accomplished on receipt of the airmail AD dated September 6, 1973, and thereafter at intervals not to exceed 50 hours time in service from the last inspection. To detect cracks in the main rotor hub P/N's 51437, 51437-6, 51437-7, 51437-8, 51437- 9, 51437-11, 51437-901, and 51437-11-911, accomplish the following: Conduct dye penetrant inspection of the main rotor hubs P/N's 51437, 51437-6, 51437-7, 51437-8, 51437-9, 51437-11, 51437-901, 51437-11-911, inside the hub in the area opposite the control rotor trunnion attachments. If cracks are found, replace with a new part before further flight and continue the 50 hour interval dye penetrant inspections. Report cracks found, model and serial number, and total time in service on the main rotor hub, to Chief, Aircraft Engineering Division, Federal Aviation Administration, Western Region, P.O. Box 92007, Worldway Postal Center, Los Angeles, California 90009. (Reporting approved by the Bureau of the Budget under B.O.B. No. 04-R0174). This amendment is effective on October 30, 1973. ## Affected data sheets (4) (OpenAirDocs) The type certificate data sheets whose models the AD names. - [TCDS 4H11](https://openairdocs.org/tcds/4H11): Siam Hiller Holdings Inc.; names 2 of 2 models: UH-12E, UH-12E-L - [TCDS 6H1](https://openairdocs.org/tcds/6H1): Siam Hiller Holdings Inc.; names 2 of 2 models: UH-12, UH-12A - [TCDS 6H2](https://openairdocs.org/tcds/6H2): Siam Hiller Holdings Inc.; names 2 of 2 models: UH-12C, UH-12B - [TCDS 4H10](https://openairdocs.org/tcds/4H10): Siam Hiller Holdings Inc.; names 1 of 1 models: UH-12D ## 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: 222 (222 by airframe model, 0 by engine model) - Makers: Hiller 210, Hiller - World Helicopters 2, Hiller-Osborn 2, Hiller-Felt 1, Hiller-Heli-Cab 1, Hiller-Helicopter Rep SVC 1, Hiller-Rogerson Helicopter 1, Hiller-Stanley 1, Hiller-Tri-Plex Ind.Inc. 1, Hiller-Trident Helicopters 1 Models with the most aircraft: - [Hiller UH-12E](https://openairdocs.org/model/hiller-uh-12e): 103 aircraft (airframe model) - [Hiller UH-12B](https://openairdocs.org/model/hiller-uh-12b): 35 aircraft (airframe model) - [Hiller UH-12C](https://openairdocs.org/model/hiller-uh-12c): 31 aircraft (airframe model) - [Hiller UH-12D](https://openairdocs.org/model/hiller-uh-12d): 22 aircraft (airframe model) - [Hiller UH-12A](https://openairdocs.org/model/hiller-uh-12a): 16 aircraft (airframe model) - [Hiller UH-12](https://openairdocs.org/model/hiller-uh-12): 2 aircraft (airframe model) - [Hiller - World Helicopters UH-12C](https://openairdocs.org/model/hiller-world-helicopters-uh-12c): 2 aircraft (airframe model) - [Hiller-Osborn UH-12D](https://openairdocs.org/model/hiller-osborn-uh-12d): 2 aircraft (airframe model) - [Hiller-Yehnert UH-12](https://openairdocs.org/model/hiller-yehnert-uh-12): 1 aircraft (airframe model) - [Hiller-Stanley UH-12C](https://openairdocs.org/model/hiller-stanley-uh-12c): 1 aircraft (airframe model) - [Hiller-Felt UH-12C](https://openairdocs.org/model/hiller-felt-uh-12c): 1 aircraft (airframe model) - [Hiller UH-12E-L](https://openairdocs.org/model/hiller-uh-12e-l): 1 aircraft (airframe model) - [Hiller-Helicopter Rep SVC UH-12B](https://openairdocs.org/model/hiller-helicopter-rep-svc-uh-12b): 1 aircraft (airframe model) - [Hiller-Tri-Plex Ind.Inc. UH-12B](https://openairdocs.org/model/hiller-tri-plex-ind-inc-uh-12b): 1 aircraft (airframe model) - [Hiller-Trident Helicopters UH-12C](https://openairdocs.org/model/hiller-trident-helicopters-uh-12c): 1 aircraft (airframe model) - [Hiller-Heli-Cab UH-12B](https://openairdocs.org/model/hiller-heli-cab-uh-12b): 1 aircraft (airframe model) - [Hiller-Rogerson Helicopter UH12E](https://openairdocs.org/model/hiller-rogerson-helicopter-uh12e): 1 aircraft (airframe model) All 18 models: https://openairdocs.org/ad/73-20-03/models.md Every aircraft: https://openairdocs.org/ad/73-20-03/aircraft.md Its text cites no advisory circulars or STCs. ## NTSB investigations that cite this AD (2) From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. - [NTSB CEN22LA318](https://openairdocs.org/ntsb/CEN22LA318), Jul 6, 2022: Hiller UH12E (N64272), Becker, MN, substantial damage. Probable cause: The in-flight failure of the main rotor mast hub due to several undetected fatigue fractures. - [NTSB LAX95LA096](https://openairdocs.org/ntsb/LAX95LA096), Feb 3, 1995: Hiller UH-12E (N9293Z), Chowchilla, CA, destroyed. Probable cause: the in-flight failure and separation of the main rotor hub due to a fatigue crack. --- 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.