AD 56-17-03
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| engine | Hartzell Propeller, Inc. | HC-12X20-1 | HARTZELL Model HC-12X20 Reversing Propellers |
| engine | Hartzell Propeller, Inc. | HC-12X20-2 | HARTZELL Model HC-12X20 Reversing Propellers |
| engine | Hartzell Propeller, Inc. | HC-12X20-3 | HARTZELL Model HC-12X20 Reversing Propellers |
| engine | Hartzell Propeller, Inc. | HC-12X20-4 | HARTZELL Model HC-12X20 Reversing Propellers |
| engine | Hartzell Propeller, Inc. | HC-12X20-5 | HARTZELL Model HC-12X20 Reversing Propellers |
| engine | Hartzell Propeller, Inc. | HC-12X20-6 | HARTZELL Model HC-12X20 Reversing Propellers |
| engine | Hartzell Propeller, Inc. | HC-12X20-7 | HARTZELL Model HC-12X20 Reversing Propellers |
| engine | Hartzell Propeller, Inc. | HC-12X20-8 | HARTZELL Model HC-12X20 Reversing Propellers |
| engine | Hartzell Propeller, Inc. | HC-12X20-9 | HARTZELL Model HC-12X20 Reversing Propellers |
Unsafe Condition
Failure of the valve tube A-57 due to vibration and weakening effect of the valve porthole, which could allow the propeller to go into reverse under certain conditions, forcing the airplane to land.
AI-generated summary from the source AD text. Verify against the official source before acting.
Required Actions
Disassemble the valve assembly and inspect the A-57 valve tube around the valve port with a magnifying glass or magnetic inspection equipment. If no cracks are found, round the sharp edges at the sides of the porthole using a fine round file.
AI-generated summary from the source AD text. Verify against the official source before acting.
Compliance Time
as soon as possible but not later than next 25 hours of operation and each 100 hours flight time thereafter
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Affected Aircraft
Hartzell Propeller, Inc. Model HC-12X20 Reversing Propellers installed on Downer (Republic) RC-3 Aircraft with B-55 Valve Assembly
AI-generated summary from the source AD text. Verify against the official source before acting.
Source: Official FAA Source ↗
Retrieved: Apr 8, 2026
Rights: U.S. Government Public Domain
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