Rolls-Royce is developing software to address a “design issue” that puts certain Trent 1000-powered Boeing 787s at risk of fuel flow restrictions under certain conditions. 

In the meantime, operators are being told to follow revised refueling limitations that raise minimum temperatures. 

The FAA in a draft airworthiness directive (AD) issued April 14 outlined the issue and temporary risk-mitigation measures. 

Rolls “discovered and reported to Boeing that a design issue in the engine fuel feed system could result in fuel flow restrictions to both engines when ice that has accumulated in the airplane fuel feed system suddenly releases into the engines,” the draft directive said. “The sudden release of accumulated ice into the engine fuel feed system, in combination with low fuel temperatures, could cause freezing temperatures at the inlet of certain engine fuel feed system components.” 

Boeing informed the FAA about the issue, and the agency moved to mandate the temporary risk-mitigation measures, which, if finalized as proposed, would give operators 30 days to modify their procedures. Boeing and Rolls are “developing updated electronic engine control (EEC) software, which will change the engine oil temperature amber line indicated in the engine indication and crew alerting system (EICAS),” the FAA said. “This change will ensure that, before takeoff, the engine oil temperature would be warm enough to operate the engine with cold fuel,” the agency said in the AD. “The updated EEC software combined with the action required by this proposed AD will address the unsafe condition identified in this AD.” 

Rolls confirmed the software is “in development” and would be mandated “through subsequent ADs.” It declined to provide a time line. 

“As we work this through with Boeing and the relevant airworthiness authorities, we will be updating our customers on progress and availability,” the engine manufacturer said in response to an Aviation Week inquiry. 

Rolls said the issue has not led to any in-service events on the 787 fleet, nor is it related to any other issues of fuel feed ice blockage.  

Ice that formed from water in fuel, released, and blocked flow at the fuel oil heat exchanger was determined to be the cause of Rolls-powered British Airways Boeing 777 landing short of London Heathrow Airport Runway 27 Left in a January 2008 accident.  

“Certification requirements ... did not take account of this phenomenon as the risk was un-recognized at that time,” the UK Air Accidents Investigation Branch said in its 2010 final report. 

Among the recommendations that came from the probe: AAIB urged regulators to “consider the implications of the findings of this investigation on other certificated airframe/engine combinations.”