AD 99-04-04
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| aircraft | Lycoming Engines | IO-540-K1A5 | Airworthiness Directives; Textron Lycoming Reciprocating Engines IO-540 and O-540 Engines Equipped With Slick Aircraft Products Magnetos |
| aircraft | Lycoming Engines | IO-540-K1B5 | Airworthiness Directives; Textron Lycoming Reciprocating Engines IO-540 and O-540 Engines Equipped With Slick Aircraft Products Magnetos |
| aircraft | Lycoming Engines | IO-540-K1G5 | Airworthiness Directives; Textron Lycoming Reciprocating Engines IO-540 and O-540 Engines Equipped With Slick Aircraft Products Magnetos |
| aircraft | Lycoming Engines | O-540-B2B5 | Airworthiness Directives; Textron Lycoming Reciprocating Engines IO-540 and O-540 Engines Equipped With Slick Aircraft Products Magnetos |
| aircraft | Lycoming Engines | O-540-B2C5 | Airworthiness Directives; Textron Lycoming Reciprocating Engines IO-540 and O-540 Engines Equipped With Slick Aircraft Products Magnetos |
| aircraft | Lycoming Engines | O-540-E4B5 | Airworthiness Directives; Textron Lycoming Reciprocating Engines IO-540 and O-540 Engines Equipped With Slick Aircraft Products Magnetos |
| aircraft | Lycoming Engines | O-540-E4C5 | Airworthiness Directives; Textron Lycoming Reciprocating Engines IO-540 and O-540 Engines Equipped With Slick Aircraft Products Magnetos |
| aircraft | Lycoming Engines | O-540-G1A5 | Airworthiness Directives; Textron Lycoming Reciprocating Engines IO-540 and O-540 Engines Equipped With Slick Aircraft Products Magnetos |
| aircraft | Lycoming Engines | O-540-G2A5 | Airworthiness Directives; Textron Lycoming Reciprocating Engines IO-540 and O-540 Engines Equipped With Slick Aircraft Products Magnetos |
Unsafe Condition
Failure of the magneto impulse coupling pawl due to excessive wear caused by vibratory forces, leading to engine seizure.
AI-generated summary from the source AD text. Verify against the official source before acting.
Required Actions
Inspect the magneto impulse coupling pawls for wear and proper operation in accordance with Textron Lycoming SB No. 537. Replace the impulse coupling assembly if wear or damage is found. Perform initial inspection within 10 hours time-in-service (TIS) from the AD's effective date or by 250 hours TIS since new/overhauled, whichever is later, then repetitive inspections every 250 hours TIS from the last inspection or overhaul.
AI-generated summary from the source AD text. Verify against the official source before acting.
Compliance Time
Initial inspection within 10 hours time-in-service (TIS) from the effective date of this AD if the magneto has been in service for more than 250 hours TIS since new or overhauled, or within 10 hours TIS from the effective date or by 250 hours TIS since new or overhauled whichever is later if the magneto has been in service for less than 250 hours TIS since new or overhauled; then repetitive inspections every 250 hours TIS from the last inspection or overhaul.
AI-generated summary from the source AD text. Verify against the official source before acting.
Affected Aircraft
Textron Lycoming O-540-B2B5, B2C5, E4B5, E4C5, G1A5, G2A5, IO-540-K1A5, K1B5, and K1G5 engines equipped with Slick Aircraft Products magnetos model numbers 6251, 6252, 6255, 6351, and 6355.
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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