# AD 55-19-01: Tail Boom Rear Bulkhead

- Type: Airworthiness directive
- Status: Current
- Products: Hiller UH-12, UH-12A and UH-12B
- Superseded by: Nothing supersedes this AD
- Product type: Aircraft, Rotorcraft
- Registered aircraft: 57 may be affected, by airframe or engine model (OpenAirDocs)
- FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/26BD249CC471D39786256A38005F0C7E.0001
- DRS record last changed: May 30, 2024
- Page: https://openairdocs.org/ad/55-19-01

## The airworthiness directive

55-19-01 HILLER: Applies to All UH-12, UH-12A, and UH-12B Model Helicopters.

Compliance required as indicated.

There have been several instances of cracking and failure of the tail boom rear bulkhead casting adjacent to the gearbox attachment holes. Cause of the cracking is not definitely known, but may be caused by flight loads or by damage incurred when the bulkhead is riveted to the tail boom. The following inspections are required:

  (1) Prior to the next flight and every 25 hours operating time thereafter, remove the tail rotor gearbox in accordance with the pertinent Hiller Service Manual. Inspect the tail boom rear bulkhead P/N 62201 for evidence of cracking, using dye or fluorescent penetrant methods.

  (2) Daily inspect the visible portions of the tail boom rear bulkhead P/N 62201 for visible evidence of cracking or failure.

  (3) If cracks or other damage are found during the above inspections, the P/N 62201 (magnesium) bulkhead must be scrapped andreplaced with the P/N 62202 (aluminum) bulkhead in accordance with Hiller Service Bulletin No. 49, revised August 23, 1955, prior to further flight. If a P/N 62202 bulkhead is not available, a new P/N 62201 bulkhead may be installed provided the inspections called for in paragraphs (1) and (2) are continued.

## Affected data sheets (2) (OpenAirDocs)

The type certificate data sheets whose models the AD names.

- [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 1 of 2 models: UH-12B

## 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: 57 (57 by airframe model, 0 by engine model)
- Makers: Hiller 53, Hiller-Heli-Cab 1, Hiller-Helicopter Rep SVC 1, Hiller-Tri-Plex Ind.Inc. 1, Hiller-Yehnert 1

Models with the most aircraft:

- [Hiller UH-12B](https://openairdocs.org/model/hiller-uh-12b): 35 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-Yehnert UH-12](https://openairdocs.org/model/hiller-yehnert-uh-12): 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-Heli-Cab UH-12B](https://openairdocs.org/model/hiller-heli-cab-uh-12b): 1 aircraft (airframe model)

All 7 models: https://openairdocs.org/ad/55-19-01/models.md
Every aircraft: https://openairdocs.org/ad/55-19-01/aircraft.md

Its text cites no advisory circulars or STCs.

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