AD 66-20-04
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| engine | Lycoming Engines | IO-320-A1A | LYCOMING Model O-320, IO-320, O-340, O-360, IO-360, O-540, and IO-540 Series Engines |
| engine | Lycoming Engines | IO-320-A2A | LYCOMING Model O-320, IO-320, O-340, O-360, IO-360, O-540, and IO-540 Series Engines |
| engine | Lycoming Engines | IO-320-B1A | LYCOMING Model O-320, IO-320, O-340, O-360, IO-360, O-540, and IO-540 Series Engines |
| engine | Lycoming Engines | IO-320-B1B | LYCOMING Model O-320, IO-320, O-340, O-360, IO-360, O-540, and IO-540 Series Engines |
| engine | Lycoming Engines | IO-320-B1C | LYCOMING Model O-320, IO-320, O-340, O-360, IO-360, O-540, and IO-540 Series Engines |
| engine | Lycoming Engines | IO-320-B1D | LYCOMING Model O-320, IO-320, O-340, O-360, IO-360, O-540, and IO-540 Series Engines |
| engine | Lycoming Engines | IO-320-B2A | LYCOMING Model O-320, IO-320, O-340, O-360, IO-360, O-540, and IO-540 Series Engines |
| engine | Lycoming Engines | IO-320-C1A | LYCOMING Model O-320, IO-320, O-340, O-360, IO-360, O-540, and IO-540 Series Engines |
| engine | Lycoming Engines | IO-320-E2A | LYCOMING Model O-320, IO-320, O-340, O-360, IO-360, O-540, and IO-540 Series Engines |
| engine | Lycoming Engines | IO-360-A1A | LYCOMING Model O-320, IO-320, O-340, O-360, IO-360, O-540, and IO-540 Series Engines |
Unsafe Condition
Failure of oil filter adapter gasket, part number 74904.
AI-generated summary from the source AD text. Verify against the official source before acting.
Required Actions
Replace gasket P/N 74904 with P/N 76691. Inspect studs, cap screws, and tapped holes in the accessory housing mounting pad for proper length or depth per Lycoming Service Bulletin No. 307 or later FAA-approved revision. Replace studs, cap screws, and retap holes as necessary per the bulletin.
AI-generated summary from the source AD text. Verify against the official source before acting.
Compliance Time
within the next 50 hours' time in service after the effective date of this AD
AI-generated summary from the source AD text. Verify against the official source before acting.
Affected Aircraft
Lycoming Engines models O-320, IO-320, O-340, O-360, IO-360, O-540, and IO-540 Series Engines equipped with AC oil filters, excluding specific serial ranges as listed in the AD.
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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