The European Aviation Safety Agency (EASA) has issued an emergency airworthiness directive (AD) instructing the operators of a small group of Rolls-Royce Trent 1000 engines to ensure that no twin-engined airliner has both engines from the affected batch.

It says that any airline that operates an aircraft with two of the engines should “de-pair” them to reduce the risk of a double inflight shutdown (IFSD).

The Trent 1000 is installed primarily on the Boeing 787 and the AD applies to 15 specific engines.

Earlier this month, Air New Zealand grounded several of its 11 Boeing 787-9s after two incidents involving Trent 1000s. The carrier said the incidents were related to problems with intermediate pressure turbine blades on the early version of the engine.

The EASA directive, issued Dec. 21 and effective Dec. 22, EASA said that, following an incident where the crew of an unnamed airline shut down a Trent 1000 because of inflight vibrations and returned to the departure airport, a post-flight borescope engine inspection revealed an intermediate pressure turbine blade missing at the shank, with analysis showing this was due to corrosion.

That incident was the subject of an earlier directive mandating the removal from service of certain engines for workshop repairs.

“Since that AD was issued, prompted by further occurrences and analyses, it has been decided that, to reduce the risk of dual IFSD, a new cyclic life limit must be applied to certain engines, which determines when an engine can no longer be installed on an [airplane] in combination with certain other engines. For the reason described above, this AD requires the de-pairing of the affected engines. This AD is considered an interim action and further AD action may follow.”

In a statement, Rolls-Royce said, “This directive mandates action we are taking as part of the continual development of our pro-active engine management program.”

ATW understands that some operators of the affected engines have already de-paired them, so there are fewer than 15 still in service. Airlines that have one of the affected engines on the wing will have to ensure they do not inadvertently pair it with another from the same batch.

Alan Dron