I was a passenger on AC549 several years ago when this happened. In our case, the oxygen masks were deployed because the cabin had actually lost pressure. From the standpoint of mechanical safety, I have no doubt that these planes are built to safely withstand these rates of descent, and likely a multiple of them. Having said that, I can also say that when the plane began its (sudden and unannounced, understandably) descent, you could feel your guts up in your throat much like when the roller coaster drops over the top of the first hill. From there on down it was calmer, but nonetheless harrowing. It's hard to describe how exactly, but it sure felt like we were coming down in a hell of a hurry.

Only once we had levelled off were the flight crew able to inform us what had happened. Those intervening 6 or 8 minutes, however, were decidedly Type 3 fun.

https://globalnews.ca/news/2487158/breaking-vancouver-bound-...