# AD 75-10-01: Rotor Drive System

- Type: Airworthiness directive
- Status: Current
- Products: Hiller UH-12D, UH-12L, UH-12L4, UH-12E and UH-12E-L
- Effective: May 8, 1975
- Superseded by: Nothing supersedes this AD
- Product type: Aircraft, Rotorcraft
- Amendment: 39-2193
- Registered aircraft: 132 may be affected, by airframe or engine model (OpenAirDocs)
- FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/6E2B9ECC423B154B86256A3800601220.0001
- DRS record last changed: May 30, 2024
- Page: https://openairdocs.org/ad/75-10-01

## The airworthiness directive

75-10-01 HILLER: Amendment 39-2193. Applies to all UH-12D (Mil. H-23D, OH- 23D), UH-12E (Mil. H-23F, OH-23F, OH-23G), UH-12E-L, UH-12L and UH-12L4 helicopters certificated in all categories except those helicopters modified to incorporate Allison 250 series engines in accordance with Supplemental Type Certificate No. SH177WE or SH178WE.

Compliance required within 50 hours' time in service after the effective date of this AD unless already accomplished.

In order to prevent power loss due to slippage of the mercury clutch in the rotor drive system:

  (a) Remove the existing placard reading "No further flight if clutch engagement time exceeds 25 seconds."

  (b) Install decal placard, part number 81426-7, on the instrument panel in accordance with Hiller Service Letter 21-4 dated April 3, 1975. The placard is to read, "No further flight if clutch engagement time exceeds 20 seconds."

  (c) Incorporate the Hiller Rotorcraft Flight Manual Revision dated April 15, 1975in the applicable rotorcraft flight manual.

Equivalent modifications may be approved by the Chief, Aircraft Engineering Division, FAA Western Region.

This supersedes Amendment 39-1462 (37 F.R. 11857), AD 72-13-4.

This amendment becomes effective May 8, 1975.

## Affected data sheets (3) (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 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: 132 (132 by airframe model, 0 by engine model)
- Makers: Hiller 129, Hiller-Osborn 2, Hiller-Rogerson Helicopter 1

Models with the most aircraft:

- [Hiller UH-12E](https://openairdocs.org/model/hiller-uh-12e): 103 aircraft (airframe model)
- [Hiller UH-12D](https://openairdocs.org/model/hiller-uh-12d): 22 aircraft (airframe model)
- [Hiller UH-12L4](https://openairdocs.org/model/hiller-uh-12l4): 3 aircraft (airframe model)
- [Hiller-Osborn UH-12D](https://openairdocs.org/model/hiller-osborn-uh-12d): 2 aircraft (airframe model)
- [Hiller UH-12E-L](https://openairdocs.org/model/hiller-uh-12e-l): 1 aircraft (airframe model)
- [Hiller-Rogerson Helicopter UH12E](https://openairdocs.org/model/hiller-rogerson-helicopter-uh12e): 1 aircraft (airframe model)

All 7 models: https://openairdocs.org/ad/75-10-01/models.md
Every aircraft: https://openairdocs.org/ad/75-10-01/aircraft.md

## Related documents

- [STC SH177WE](https://openairdocs.org/stc/SH177WE): Installation of Allison 250-C20/250-C20B engine and related changes.. Siam Hiller Holdings Inc, Named in the applicability
- [STC SH178WE](https://openairdocs.org/stc/SH178WE): Installation of Allison 250-C20/250-C20B engine and related changes. (UH-12E-L (4 place)). Siam Hiller Holdings Inc, Named in the applicability

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