A PROPOSED airworthiness directive (AD) requiring replacement of the crankshafts in some 10,000 Teledyne Continental 360-and 520-series piston engines has resurfaced, with the US Federal Aviation Administration citing an abnormally high failure rate.

The original July 1993 notice of proposed rulemaking (NPRM) was strenuously opposed by the US Aircraft Owners and Pilots Association (AOPA) and National Air Transportation Association (NATA), which disputed FAA data showing that an improved crankshaft developed by Teledyne Continental had a lower failure rate. Replacement would cost around $7,000.

The FAA said then that crankshafts produced using the original "airmelt" process were more prone to sub-surface fatigue cracks than those produced using an improved "vacuum-arc remelt" process. The AOPA and NATA had cited a study by the Aeronautical Repair Station Association, which had found that both crankshaft types can develop cracks at about the same rate.

The FAA now says that it has new data showing an abnormally high failure rate for the airmelt crankshaft, compared with almost no failures for the improved component. As a result, a supplemental NPRM was issued in April calling for crankshaft replacement at the next engine overhaul. The AOPA and NATA say that the FAA has refused to release the data on which it has based its revised NPRM.

In January, the FAA scaled back a proposed AD requiring repetitive inspection of the crankshafts of certain Textron Lycoming engines. This meant that only 9,800 O-320 and O-360 Lycomings rated at 255kW (160hp) or more, instead of 46,000, were affected.

To a storm of protest from operators and the International Council of Aircraft Owner and Pilot Associations (IAOPA), the UK Civil Aviation Authority issued in 1994 an AD covering crankshaft-corrosion on a range of piston-engines built by Teledyne Continental and Textron Lycoming (Flight International, 19-26 October,1994).

Source: Flight International