I am very interested in these recent reliability events in terms of terms of ETOPS certification process. I'm wondering if a crack (pun not intended) has been found in the certification methodology that has been implemented.
To obtain ETOPS certification, a new model aircraft must conduct a mandated number of hours of operation of the engine type without shutdown required, during the certification period. However, no consideration is given or mandated based on engine wear (number of hours of operation) vs probability of failure.
To maintain a specific ETOPS certification, i.e. ETOPS 75-370, requires that the service history of aircraft using the engine type demonstrate an IFSD (in flight shut down) rate due of less than the specific rate: e.g. 0.01% per 1000 hours for ETOPS 180.
Herein lies the problem. The IFSD rate is averaged across all engines of the certified type, regardless of operational hours. It does not take in the scenario where newer engines are extremely reliable and older engines have a dramatic drop in the reliability rate.
If separate samples were taken by say every 1000 hours of engine life, with the ETOPS rating concurrent with the average IFSD within each 1000 hour period, then I would feel comfortable, but this isn't the methodology used. The high reliability of newer engines (higher at the moment for the B787 as a newer model) can mask the effective unreliability of high operational hour engines.