There have been three significant airliner engine failures in 72 hours. All aircraft survived. All are Boeing; 777 (Denver), 747 (Maastricht) and 737 (Makassar.)

That's a lot of engine failures. It's hard to find a common mode here, other than they're Boeing, which is next to meaningless; the engines and airframes are all very different.

Still, it's hard to overcome instinct. "Once is happenstance. Twice is coincidence. Three times is enemy action."

(It's a quote from Ian Fleming; I'm not suggesting any sort of 'attack,' only that some common mode phenomenon could be in play)

We get 4 or 5 and we're going to have to look at this really hard. If I had a gun to my head when asked what is going on I would speculate that perhaps these engines need more scrutiny before returning to service after a long COVID-19 hiatus. But then I don't actually know if that was even the case for any or all of the engines involved.

The engine lost its shrapnel barrier. It it had managed to ingest debris, the fans could have blown their way through the fuselage, killing anyone in the line of fire. Something is to blame for an event that is never supposed to happen.

You don't know that. The mechanic could have been following a P&W procedure that did not account for some wear in the engine. Is that mechanic even a United employee or P&W or a contractor? The mechanic could have installed the wrong part. It could have been a totally random part failure. I can go on. There's too many possibilities to speculate at this point. Reports say the engine was vibrating before the cowling came off. That could be caused by many factors. It could have been a bird strike. The plane in front could have lost an engine or tire and this one sucked up FOD. We just do not know yet. The plane landed, the engine will be inspected.

Bird strikes generally do not cause engines to explode. The 777 engines in particular were specifically designed to be survive ingestion of frozen turkeys.