In a final airworthiness directive (AD) to be published Friday, the FAA has rebuffed efforts by both the Air Line Pilots Association International (ALPA) and the US National Transportation Safety Board (NTSB) to acclerate a mandated hardware fix with a 2011 deadline for Boeing 777 operators with Rolls-Royce Trent 800 turbofan engines.

The action stems from the crash of a Rolls-Royce-powered Boeing 777 at Heathrow Airport last year in which accumulated ice in the engine's fuel-oil heat-exchanger (FOHE) is suspected of blocking fuel flow to both engines. The same phenomena likely caused a similar in-flight incident with one engine of a Delta Air Lines 777 in November of 2008.

An interim AD issued in March of this year called on operators to follow certain operational guidelines designed to prevent ice from forming, including in-flight and ground measures.

European regulators in July mandated that airlines close out the interim AD by equipping aircraft with a redesigned Rolls-Royce FOHE, a device that is supposed to cool the engine oil while at the same time pre-heating the incoming fuel to prevent any water present from freezing. EASA gives operators 6,000 flight hours from July or until 1 January 2011 to make the fix, whichever occurs first.

The FAA final AD to be issued Friday gives operators the same lead time, with the clock starting in early January.

However, ALPA and NTSB have expressed concerns over potential safety issues during the compliance period.

In comments to the proposed rulemaking, issued in July, ALPA requested that the compliance time be set as soon as six months after the January effective date for the AD as interim procedures call for "an immediate idle descent to melt the blockage" in the case of an engine rollback.

Union concerns include the potential for traffic conflicts during such descents in remote areas with no radar separation.

"This engine rollback is very insidious to the crew and creates the potential for a pilot to be faced with an immediate descent without adequate time to compensate for traffic, weather, or terrain," ALPA states.

Fearing similar incidents, NTSB had called on the FAA to mandate that at least one engine on each affected aircraft be modified with the redesigned FOHE by the end of December this year.

"The NTSB believes that the January 1, 2011 compliance date for installation of the new FOHE is not consistent with the risk associated with the original FOHE design."

The FAA rebuffed both requests however, telling the organizations that the interim operational procedures would "assure continued safe operation until hardware modifications become available".

Source: Air Transport Intelligence news