What does it mean when an aircraft engine is de-paired? e.g. the PW1000g engines being de-paired because of issues in the LPT or the Rolls Royce Trent 1000 engines due to excessive corrosion on some of the turbine blades?
De-pairing means literally braking up pairs. In the case in question, it means that if an aircraft is equipped with engines of a certain specific type, one of the engines has to be replaced with a version that has been upgraded.
The reason for the de-pairing is to mitigate the risk of a dual engine failure: Having two engines that are both affected by the same issue considerably increases the risk of both engines failing on the same flight. At least RR Trent 1000 and P&W 1100G have been issued a de-pairing AD by EASA.