# AD 56-27-04: Engine Cooling Kit Removal

- Type: Airworthiness directive
- Status: Current
- Products: Sierra Hotel Aero Navion B
- Superseded by: Nothing supersedes this AD
- Product type: Aircraft, Small airplane
- Registered aircraft: 113 may be affected, by airframe or engine model (OpenAirDocs)
- FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/C6B6B3DA757F320B86256A56006FC857.0001
- DRS record last changed: May 30, 2024
- Page: https://openairdocs.org/ad/56-27-04

## The airworthiness directive

56-27-04 NAVION: Applies to B Type Aircraft Equipped with Reading Aviation Service Inc. or Hackenberk Sales and Service Downdraft Cooling Kit Installations.

Compliance required not later than July 1, 1957.

Engine cooling tests conducted subsequent to the installation of these kits reveal that cylinder head and oil temperature values can exceed established limits. To prevent serious damage to the engines in these aircraft due to overheating, one of the following alternate actions is necessary.

1. Remove Reading Aviation Service Inc. or Hackenberg Aviation Sales Service downdraft cooling kit and return aircraft to the original Ryan cooling configuration, or

2. Modify the Reading or Hackenberg engine cooling kit in accordance with Reading Aviation Service Inc. Service Bulletin No. 1 dated July 26, 1956.

## Affected data sheets (1) (OpenAirDocs)

The type certificate data sheets whose models the AD names.

- [TCDS A-782](https://openairdocs.org/tcds/A-782): Sierra Hotel Aero Inc.; names 1 of 8 models: Navion B

## 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: 113 (113 by airframe model, 0 by engine model)
- Makers: Ryan 68, Navion 42, North American 3

Models with the most aircraft:

- [Ryan NAVION B](https://openairdocs.org/model/ryan-navion-b): 68 aircraft (airframe model)
- [Navion NAVION B](https://openairdocs.org/model/navion-navion-b): 42 aircraft (airframe model)
- [North American NAVION B](https://openairdocs.org/model/north-american-navion-b): 3 aircraft (airframe model)

All 3 models: https://openairdocs.org/ad/56-27-04/models.md
Every aircraft: https://openairdocs.org/ad/56-27-04/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.