# AD 81-18-02: Tail Rotor Skin Cracks - Type: Airworthiness directive - Status: Current - Products: Hiller UH-12, UH-12A, UH-12B, UH-12C, UH-12D, UH-12L, UH-12L4, UH-12E and UH-12E-L - Effective: September 10, 1981 - Superseded by: Nothing supersedes this AD - Product type: Aircraft, Rotorcraft - Amendment: 39-4203 - Registered aircraft: 225 may be affected, by airframe or engine model (OpenAirDocs) - FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/D3121348AAB8C00986256A4E0043B8AC.0001 - DRS record last changed: May 30, 2024 - Page: https://openairdocs.org/ad/81-18-02 ## The airworthiness directive 81-18-02 HILLER AVIATION: Amendment 39-4203. Applies to Hiller Model UH-12 series helicopters including military models H-23F and OH-23G, certificated in all categories. Compliance required as indicated, unless already accomplished. To prevent tail rotor skin cracks, accomplish the following: (a) Prior to further flight after the effective date of this AD; 1) Visually inspect the tail rotor blades for skin cracks or loose rivets. If cracks or loose rivets are found, replace with like serviceable part prior to return to service. 2) Inspect the four vent holes in the tail rotor blades for obstruction as indicated in Part 2 of Hiller Aviation Service Bulletin UH-12-55-1 dated August 11, 1981. If either of the vent holes at the root end are found to be obstructed, remove the blade from service and replace with like serviceable part. If the root vent holes are found to be unobstructed, inspect the tip vent holes and clear of any obstruction prior to returnto service. (b) Prior to each flight after the inspections required by paragraph (a) of this AD, conduct a visual check to determine that the four vent holes are clear of obstruction. If obstructions are found, perform the appropriate corrective actions of paragraph (a) of this AD prior to further flight. NOTE: The checks required by paragraph (b) of this AD may be performed by the pilot. NOTE: For the requirements regarding recording compliance and method of compliance with this AD in the aircraft's permanent maintenance records, see FAR 91.173. (c) Special flight permits may be issued in accordance with FAR 21.197 and 21.199 to operate airplanes or helicopters to a base for the accomplishment of inspections or modifications required by this AD. (d) Alternative inspections, modifications or other actions which provide an equivalent level of safety may be used when approved by the Chief, Engineering and Manufacturing Branch, FAA Western Region. The manufacturer's specifications and procedures identified and described in this directive are incorporated herein and made a part hereof pursuant to 5 U.S.C. 552(a)(1). All persons affected by this directive, who have not already received these documents from the manufacturer, may obtain copies upon request to Hiller Aviation, 2075 W. Scranton Avenue, Porterville, California 93257, telephone (209) 781-8000. These documents may also be examined at FAA Western Region Office, 15000 Aviation Boulevard, Hawthorne, California 90261 and at FAA Headquarters, 800 Independence Avenue, S.W., Washington, D.C. 20591. A historical file on this AD, which includes the incorporated material in full is maintained by the FAA at its headquarters in Washington, D.C. and at FAA Western Region Office. This amendment becomes effective September 10, 1981. ## Affected data sheets (5) (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 H1WE](https://openairdocs.org/tcds/H1WE): Siam Hiller Holdings Inc.; names 2 of 2 models: UH-12L4, UH-12L - [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: 225 (225 by airframe model, 0 by engine model) - Makers: Hiller 213, 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-12L4](https://openairdocs.org/model/hiller-uh-12l4): 3 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 19 models: https://openairdocs.org/ad/81-18-02/models.md Every aircraft: https://openairdocs.org/ad/81-18-02/aircraft.md 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.