US regulators are directing General Electric-powered Boeing 747 and 767 operators to adopt a procedural change aimed at reducing the potential risk of engine flame-out during descent in icing conditions.
The Federal Aviation Administration said the directive had been prompted by reports of "several" in-flight engine flame-outs, among them "multiple" dual-engine flame-outs.
One event in November 2007, it added, involved three multi-engine flame-outs and, at one point, a three-engine flame-out.
The FAA's advisory is centred on activation of wing and nacelle anti-ice prior to descent on 747s and 767s with CF6-80C2 or -80A engines.
But the change drew objections from GE which disagreed with the FAA's opinion that an unsafe condition was likely to exist, pointing out that there had never been an instance in which a CF6-80C2 engine had failed to relight rapidly.
GE also argued that, with 1,064 aircraft in the global fleet affected, the proposed procedures would create an "environmental burden", said the FAA, through additional fuel burn.
"GE believes the extremely improbable rate of dual-engine flame-outs coupled with the adverse environmental impact outweigh the benefits of the proposed [aircraft flight manual] procedure," it stated, adding that GE requested withdrawal of the proposal.
But the FAA said it did not agree with GE, claiming that evaluation had found "sufficient data" to demonstrate that under certain conditions a flame-out could also cause engine damage which would potentially prevent a relight.
Delta Air Lines and Japan Airlines requested that the procedural change should apply only in the vicinity of convective weather, but the FAA rejected this argument as well.
"Service experience has demonstrated that flight crews are not always able to differentiate between ice-crystal icing that causes engine flame-out and other types of visible moisture that typically do not lead to engine flame-outs," it said.
"Therefore, relying on flight crews to recognise the necessary weather conditions might not provide an adequate level of safety."