European safety regulators have identified another suspected dual-engine icing event, involving a Rolls-Royce-powered Airbus A330, and ordered precautionary measures centred on the water scavenge system.
During take-off, the aircraft's right-hand Trent 700 engine suffered a temporary shortfall in engine thrust - prompting an 'engine stall' warning - before it recovered.
Investigation showed that fuel flow to the right-hand engine had been restricted. But it also determined that the left-hand engine had experienced a similar flow restriction shortly afterwards.
This thrust shortfall on the left-hand engine had been "insufficient to trigger any associated warning", says the European Aviation Safety Agency, adding that it was "only noted through analysis of the flight data".
After the initial 'engine stall' warning on the right-hand powerplant, the pilots responded with standard procedures, which included retarding the throttle to idle.
No action was required to restore thrust on the left-hand engine. Both engines recovered fully and the remainder of the flight was uneventful.
EASA has not disclosed the identity of the carrier or the location of the incident, describing it only as a "recent in-service event".
But it says: "Based on previous industry-wide experience, the investigation of the event has focused on the possibility for ice to temporarily restrict the fuel flow."
While no fuel system fault has been identified, EASA says the operation of the water-scavenge system, located at wing rib 3, "cannot be excluded" as a contributing factor.
EASA has issued an emergency airworthiness directive ordering the operators of Trent-powered A330s to deactivate the automatic standby fuel pump scavenge system which operates during taxiing and take-off. It is also prohibiting dispatch of aircraft with any main fuel pump inoperative.
"Testing and analysis are continuing to identify the root cause of the event," it adds.
Restriction of fuel to the engine, as a result of ice accumulation, has become a high-profile concern since the dual-engine accident involving a Trent 800-powered British Airways Boeing 777 at London Heathrow in January 2008.
Ice-related fuel restriction on Trents is also suspected in single-engine incidents involving a Delta Air Lines 777 in cruise and an Etihad Airways A330 during a go-around at Manchester.
EASA has already mandated a modification to the fuel-oil heat exchanger in Rolls-Royce Trent 800, 700 and 500 engines. It has not been confirmed whether or not the A330 involved in the incident had been modified.
Source: Air Transport Intelligence news