Originally Posted by
Intruder
Nobody knows exactly what the blade hit on its way out, and what else in the cowling was cut off in what direction. It is entirely possible that a piece of something from/in the cowl ricocheted and hit the window.
This!
It seems strange to me that so many people here seem focused on generating
magic bullet theories about how the departed fan blade struck a cabin window well aft of the event when most of the damage to the cowling was due to engine imbalance.
Is it so hard to believe that the massive forces shaking the cowling apart could to throw debris into the air-stream with sufficient force to dislodge a cabin window?
Given the delay between the initial blade failure and the window failure, I think the evidence available supports the hypothesis that pieces of the cowl, or other secondary debris struck the window as the unbalanced engine wound down.
I've seen enough footage of imbalanced rotating objects destroying things to know you should never underestimate the devastating effects such phenomena can have on their surroundings.
Note that in the first two videos below, the engines are mounted in test stands which are far more rigid than an airplane's engine pylon. In flight, I would expect a lot more movement of the engine during wind-down:
These videos are of helicopters, but illustrate how quickly things can go wrong when rotating parts are no longer balanced: