To clarify, I'm an aviation enthusiast, not a pilot. I have a question for ATR pilots (or anyone with knowledge of the ATR systems).
While travelling on an ATR-72, about 15 mins after takeoff (and presumably at cruising altitude) I felt a very rapid deceleration - to the point I felt pressure on the seatbelt. At the same moment, I felt a sudden change in the air pressure. Checking my altimeter-measuring watch, I saw a reading of 760mb - well bellow the normal ~1000. No masks dropped, however. Several people in the cabin became upset and worried. I was sitting on the second row and, although I can't be certain behind the closed door, I'm pretty sure I heard a 'whoop whoop' alert from the cockpit.
The journey continued without diversion or any emergency landing (frustratingly, no crew announcement either). I did notice that the air pressure remained bellow 800mb for the rest of the ~30min flight, beginning to rise only during descent.
I was wondering if anyone has a clue what might have happened. My best guess is some sort of engine trouble leading to bleed air problems, causing the plane to fly at a lower altitude (unpressurized) for the rest of the flight. But then again, is it normal procedure not to divert/return? I should mention that we had departed a large metropolitan airport headed for a regional one, so a return to the largest, better-equipped airport made more sense, I would think.