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IO-520s.

The following information is derived from the FAA's Service Difficulty Reports and Aviation Maintenance Alerts.

BEECHCRAFT MODEL F33A BONANZA/IO-520

Cracked Magneto Impulse Coupling

During a 500-hour magneto inspection, the impulse coupling was discovered to have cracks in its flyweight base plate. The cracks were detected using magnetic particle inspection and appear to have originated from the sharp-cornered feature of the base plate that forms the full advance stop. Slick p/n M3050.

Part total time: 565.0 hours

BEECHCRAFT MODEL A36 BONANZA/IO-520

Cracked Magneto Impulse Coupling

Impulse coupling found cracked at advance stop notches of base plate. Defect was discovered using magnetic of part during performance of manufacturer's recommended 500-hour inspection. Both magnetos (Slick p/n M3050) on this engine show same defect.

Part total time: 1000.0 hours

BEECHCRAFT MODEL 58 BARON/IO-520

Cracked Cylinder Heads

On descent to destination, the left engine started backfiring when power was reduced. Examination found #1 and #3 cylinder heads cracked. Aircraft returned to service after cylinders were replaced. Part total time: 767.0 hours

CESSNA A185F/IO-520

Crankshaft Failure

The engine sustained a catastrophic failure. Examination revealed crankcase fretting on #2 and #3 intermediate bearing saddle thru-bolt pads. After the main bearings became loose, the bearing tangs wore and the main bearing in the #2 position started to come apart, allowing the other half of the bearing to move and ride up into the crankshaft radius, creating a stress riser. The crankshaft broke at the #2 main journal.

Part total time: Unknown

CESSNA 207/IO-520

Failed Starter Drive Adapter

The pilot reported the starter was slipping. Examination revealed the starter drive adapter spring was broken and had damaged the crankshaft gear retaining bolts and safety wire. The safety wire was broken, possibly resulting in oil system contamination. The engine will need to be replaced due to the oil contamination caused by the starter drive adapter failure. Part total time: 471.0 hours

CESSNA 207A/IO-520

Broken Magneto Distributor Gear

The left (Bendix) magneto failed in flight. Examination revealed the magneto's distributor gear was broken. Further inspection revealed the right magneto had a 200-rpm drop, which is out of specification. A thorough inspection of the engine revealed the #4 cylinder showed signs of detonation. The engine will be replaced.

Part total time: 1400.0 hours

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Title Annotation:SQUAWX BOX
Publication:Aviation Safety
Date:Nov 1, 2017
Words:384
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