Reports of eight in-flight and four on-ground unintended shutdowns of General Electric CF6-80C2B wide-body turbofan engines have prompted the US Federal Aviation Administration (FAA) to mandate a change out of the engine's electronic control unit (ECU).
A proposed airworthiness directive, to be published on 14 November, will affect 697 CF6 engines flying on US-registered widebody aircraft. The directive supersedes a 2007 AD requiring a software upgrade (8.2.Q1) on the same ECU to increase the engine's margin to flameout after several incidents where engines had flamed out due to exposure to ice crystals and ice shedding into the engine.
With the new software in place, problems continued. FAA said it received two reports of "ice crystal condition flameouts", which prompted GE to develop another software upgrade (8.2.R) for the ECU. The new software included "improved inclement weather capability, and enhanced fuel metering valve fault handling logic to reduce the risk of [in-flight shut down] caused by intermittent fuel metering valve feedback signals", said the FAA.
Since that time however, there have been 12 additional engine shutdowns, eight in flight and four on the ground, with engines using upgraded ECU software and other upgrades. The problem was found to be caused by ignition system induced noise that created dual-channel faults in the ECU computer.
In response, the proposed AD mandates replacing the ECUs with a new unit developed by GE to "eliminate the potential for dual-channel [computer] faults due to ignition system noise".
If finalised as written, the 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 ECU part number.