THE US FEDERAL Aviation Administration has ordered repetitive ultrasonic and electro-magnetic testing of General Electric CF6 engine high-pressure compressor (HPC) spools (Flight International 25-31 October).

The Airworthiness Directive (AD) guards against fatigue cracking caused by hard-alpha inclusions (titanium-alloy impurities caused during manufacture) and dwell-time fatigue, a type of fatigue-cracking which occurs when the peak cyclic load is sustained at a relatively low temperature. The AD covers the 3-9 spool of the high-pressure compressor in GE CF6-45, -50, -80A and 80C2 turbofan engines.

About 5,000 CF6 engines are in operation worldwide, including 825 in service on US-registered aircraft. The turbofan powers numerous commercial airliners, including the Airbus A300 and A310, the Boeing 747 and 767, and the McDonnell Douglas DC-10 and MD-11.

In August, the US National Transportation Safety Board urged the aviation agency to issue an AD requiring inspection of the CF6 spools for cracks. General Electric issued a service bulletin recommending improved fluorescent penetrant inspections. In September, the FAA made the GE-recommended inspections mandatory.

The directive was implemented as a result of engine failures on a CF6-50C2-powered A300B4 operated by Egyptair and a Thai International CF6-50C2B-powered DC-10.

Source: Flight International