Prop NPRM Affects Bonanzas, Navions

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About 2350 Beech Bonanzas, T-34s and Navions with certain prop and engine combinations will fall under a proposed Airworthiness Directive that will require immediate replacement of the prop on about 500 of the affected aircraft and RPM limits on the others. Based on test data supplied by McCauley, the FAA issued a Notice of Proposed Rulemakingcovering 3A32C406/82NDB–X and D3A32C409/82NDB–X propellers, installed on Continental IO–520, TSIO–520 or IO–550 engines, saying McCauley's testing "identified stress conditions that affect the fatigue life and damage tolerance" of the props. AOPA is challenging the NPRM, saying there's no accident data to back up the proposed AD. The NPRM sets the service life of the affected props at 10,000 hours and requires that any props for which the accumulated hours to date are unknown also be replaced. The others will be under an operating restriction that prohibits continued operation between 2,350 and 2,450 RPM with a manifold pressure of more than 24 inches. The props will also undergo inspections for cracks every 100 hours and blades must be replaced ($10,500 per blade plus labor) or repaired as required.