Rolls-Royce is investigating further operational issues with Trent 1000 engines, after instances of surges involving certain powerplants – a situation which has triggered a de-pairing order from European regulators.

Trent 1000s, which are fitted to Boeing 787s, have already been the subject of several regulatory interventions, particularly as a result of problems with blade durability.

But the surge occurrences appear to be a separate issue. “Investigation into the cause [or causes] of these events is ongoing,” says the European Union Aviation Safety Agency.

EASA says the engine surges have particularly affected engines which have accumulated a high number of cycles and flight hours.

It says there is a risk of dual engine surge, possibly leading to a dual engine shutdown.

Rolls-Royce has drawn up a service bulletin giving instructions to de-pair certain engines in order to reduce the risk of a dual surge incident.

EASA is mandating this de-pairing scheme through an airworthiness directive which takes effect on 30 January.

It says Trent 1000s with over 24,000h or more than 8,000 cycles cannot be paired with a similar engine, but can be paired with engines which have fewer than 17,000h and 5,500 cycles.

But engines which have logged both 24,000h and 8,000 cycles can be paired with engines which have reached neither of these thresholds.

EASA has ordered any necessary de-pairing to be carried out within 30 days.