AD 78-12-09
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| engine | Lycoming Engines | O-320-H1AD | AVCO LYCOMING Model O-320-H Series Engines |
| engine | Lycoming Engines | O-320-H1BD | AVCO LYCOMING Model O-320-H Series Engines |
| engine | Lycoming Engines | O-320-H2AD | AVCO LYCOMING Model O-320-H Series Engines |
| engine | Lycoming Engines | O-320-H2BD | AVCO LYCOMING Model O-320-H Series Engines |
| engine | Lycoming Engines | O-320-H3AD | AVCO LYCOMING Model O-320-H Series Engines |
| engine | Lycoming Engines | O-320-H3BD | AVCO LYCOMING Model O-320-H Series Engines |
Unsafe Condition
Crankshaft gear assembly failure due to insufficient hardness of the crankshaft gear teeth.
AI-generated summary from the source AD text. Verify against the official source before acting.
Required Actions
Remove and replace the crankshaft assembly with crankshaft assembly part number LW-15917 per AVCO Lycoming Service Bulletin No. 422 or FAA-approved equivalent. Equivalent methods require approval from the FAA Eastern Region's Engineering and Manufacturing Branch.
AI-generated summary from the source AD text. Verify against the official source before acting.
Compliance Time
before further flight except that the aircraft may be flown in accordance with FAR 21.197 to a location where this AD may be accomplished
AI-generated summary from the source AD text. Verify against the official source before acting.
Affected Aircraft
AVCO Lycoming Model O-320-H1AD, O-320-H1BD, O-320-H2AD, O-320-H2BD, O-320-H3AD, O-320-H3BD engines with specific serial numbers listed in the AD, including ranges like L-1122-76 through L-1129-76 and others as enumerated.
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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