A flaw with the engine is typically in the hands of the engine manufacturer. If your (if you are General Electric or Rolls Royce) engine breaks that's a big pro

A flaw with the engine is typically in the hands of the engine manufacturer. If your (if you are General Electric or Rolls Royce) engine breaks that's a big problem and you want to figure out why, because it could ground entire fleets. Similar things happened when there were problems with the A380 and the Dreamliner - one airline has an issue, and other airlines ground their planes until Boeing/Airbus come up with fixes. A reasonably common model is that the airline effectively leases the engine, or at least contracts out maintenance to the manufacturer who also receives telemetry during flights. Saying it's an airlines fault doesn't mean much, assuming they've kept to the prescribed maintenance schedule (which may well be mandated by the manufacturer). Southwest was fined in 2008 for poor maintenance practice, but that was a decade ago now.