# AD 64-21-05: Hartzell Propeller Governor

- Type: Airworthiness directive
- Status: Current
- Products: Piper PA-23-250 (Navy UO-1) and PA-30
- Effective: September 16, 1964
- Published: September 15, 1964
- Issued: September 1, 1964
- Superseded by: Nothing supersedes this AD
- Product type: Aircraft, Small airplane
- Registered aircraft: 1,777 may be affected, by airframe or engine model (OpenAirDocs)
- FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/5D02414C2E4DD0DA862569970057FEFD.0001
- DRS record last changed: November 21, 2025
- Page: https://openairdocs.org/ad/64-21-05

## The airworthiness directive

64-21-05 PIPER: Amdt. 809 Part 507 Federal Register September 15, 1964. Applies to Model PA-30 Aircraft Equipped With the Hartzell HC-E2YL-2B/7663-4 Propeller and Model PA-23-250 Aircraft Equipped With the Hartzell HC-E2YK-2RB/8465-7R Propeller.

Compliance required as indicated.

There have been several instances of propeller failure on the Piper PA-30 aircraft. The replacement of governor relief valve springs in accordance with Hartzell Service Bulletin No. 88 dated July 2, 1964, as amended July 8, 1964, has not eliminated these failures. The propeller installation on Piper Model PA-23-250 is similar in design and operation to that used on the Model PA-30. Accordingly, this AD is being made applicable to both Models PA-30 and PA-23-250. To preclude further failures, comply with the following:

  (a) For aircraft having propellers previously serviced in accordance with Hartzell Service Bulletin No. 88 dated July 2, 1964, as amended July 8, 1964, service the propeller governors in accordance with Hartzell Service Bulletin No. 88A dated August 4, 1964, within 10 hours' time in service after the effective date of this AD.

  (b) For aircraft having propellers which have not been previously serviced in accordance with Hartzell Service Bulletin No. 88A dated July 2, 1964, as amended July 8, 1964, service the propellers in accordance with these service bulletins and, in addition, in accordance with Hartzell Service Bulletin No. 88A dated August 4, 1964, within 10 hours' time in service after the effective date of this AD.

This supersedes AD 64-16-08.

This directive effective September 16, 1964.

## Affected data sheets (2) (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-23-250 (Navy UO-1)
- [TCDS A1EA](https://openairdocs.org/tcds/A1EA): Piper Aircraft Inc.; names 1 of 3 models: PA-30

## 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: 1,777 (1,777 by airframe model, 0 by engine model)
- Makers: Piper 1,777

Models with the most aircraft:

- [Piper PA-23-250](https://openairdocs.org/model/piper-pa-23-250): 894 aircraft (airframe model)
- [Piper PA-30](https://openairdocs.org/model/piper-pa-30): 878 aircraft (airframe model)
- [Piper PA-23-250 (6PCLM)](https://openairdocs.org/model/piper-pa-23-250-6pclm): 5 aircraft (airframe model)

All 3 models: https://openairdocs.org/ad/64-21-05/models.md
Every aircraft: https://openairdocs.org/ad/64-21-05/aircraft.md

Its text cites no advisory circulars or STCs.

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