# AD 55-11-02: Thermal Relief Valves

- Type: Airworthiness directive
- Status: Current
- Products: Piper PA-23
- Published: December 4, 1956
- Issued: December 4, 1956
- Superseded by: Nothing supersedes this AD
- Product type: Aircraft, Small airplane
- Registered aircraft: 155 may be affected, by airframe or engine model (OpenAirDocs)
- FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/1043E1913F347D0E8625698B00764851.0001
- DRS record last changed: November 21, 2025
- Page: https://openairdocs.org/ad/55-11-02

## The airworthiness directive

55-11-02 PIPER: Applies to Model PA-23 Serial Numbers 23-1 to 23-142 Inclusive, 23- 144 to 23-162 Inclusive, 23-164 to 23-173 Inclusive, 23-175 to 23-177 Inclusive, 23-179 to 23- 183 Inclusive, and 23-186.

Compliance required by August 1, 1955.

In order to eliminate excessive pressures in the hydraulic system due to thermal expansion which can result in failure of the hydraulic actuating cylinders, it will be necessary to install thermal relief valves in the landing gear retraction line, landing gear extension line and the flap retraction line. These relief valves are to be installed in accordance with the sketch and instructions contained in Piper Thermal Relief Valve Kit 754 095.

(Piper Service Bulletin No. 136 dated April 26, 1955, covers this same subject.)

## Affected data sheets (1) (OpenAirDocs)

The type certificate data sheets whose models the AD names.

- [TCDS 1A10](https://openairdocs.org/tcds/1A10): Piper Aircraft Inc.; names 1 of 6 models: PA-23

## 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: 155 (155 by airframe model, 0 by engine model)
- Makers: Piper 155

Models with the most aircraft:

- [Piper PA-23](https://openairdocs.org/model/piper-pa-23): 155 aircraft (airframe model)

All 1 models: https://openairdocs.org/ad/55-11-02/models.md
Every aircraft: https://openairdocs.org/ad/55-11-02/aircraft.md

Its text cites no advisory circulars or STCs.

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