Operators of 697 General Electric CF6-80C2B turbofan engines will be required to change out engine control units within six months to six years from April due to electronic noise problems that have caused some in-flight shutdowns or on-ground flameouts.
The US Federal Aviation Administration estimates that the final rule, to be published on 24 February, will cost operators of widebody aircraft using the engines $3.4 million to implement, with each engine electronic control unit (ECU) swap taking about 4 hours of maintenance time to accomplish.
First proposed in November 2011, the AD was prompted by reports of eight in-flight shutdowns and four on-ground flameouts of the turbofan engines despite a series of earlier ECU software fixes. Those changes, prompted initially by a 2007 AD, had been designed to boost flameout margins in the presence of ice or ice crystal ingestion.
The latest problem is linked to ignition system induced noise that can cause dual-channel faults in the ECU computer, said the FAA. The new AD, which supersedes the 2007 AD, will give operators between six months (or 450 engine flight cycles) and 60 months (or 4,500 engine flight cycles) to change out the ECUs, depending on part number.
In its comments to the proposed rule before it was finalised, GE had requested that the FAA reconsider its assessment that the issues represented an unsafe condition.
"Commenter GE stated that in all events of flameout the engines relit and in all dual-channel CPU fault in-flight shutdowns the engines were capable of restarting," the FAA said. "GE stated that these events should not be considered unsafe conditions."
"We do not agree," the FAA concluded. "Although a flameout with a consecutive relight or an in-flight shutdown with a consecutive restart during cruise flight is not in itself an unsafe condition, these types of loss of thrust can be unsafe conditions during takeoff or during approach and landing."