23 November 2005
About 2350 Beech Bonanzas, T-34s and Navions with certain propeller and engine combinations are likely to be affected by a FAA proposal to adopt a new airworthiness directive for McCauley C406 and C409 props installed on Teledyne Continental IO-520, TSIO-520, or IO-550 engines. It will require immediate replacement of the prop on about 500 of the affected aircraft and RPM limits on the others.
McCauley’s testing identified stress conditions that affect the fatigue life and damage tolerance of the props. The proposed AD will set the service life of the affected props at 10,000 hours and requires that any for which the accumulated hours to date are unknown also be replaced. The remainder will be under an operating restriction prohibiting continued operation between 2,350 and 2,450 RPM with a manifold pressure of more than 24 inches. Inspections for cracks will be required every 100 hours and blades must be replaced or repaired as required. AOPA is challenging the proposed AD suggesting there is no accident data to warrant it.
