Crash reports suggest that the pilots are usually too busy trying to save the plane (or don’t realize how bad the problem is) to get on the line and tell people something bad is going to happen.
Most passengers can work out something isn’t right, though.
Yes because some may survive and they need to be able to have time to prepare
Not really, but watch the flight attendants’ faces for the real story regarding what’s about to happen.
If you really hate yourself, watch air disasters. Also, the cause of a crash can be anything from ‘dumb pilot’ to ‘wing fell off’ so it really depends
When possible they will, so you & the cabin crew can prepare for a bad landing. Sometimes there is no warning, (over running runway, loss of engine, wing etc, collision) as the pilots don’t know what is about to happen or they are too busy trying to avoid situation. If they know you are about to crash, fight checks require either an announcement to “brace” or lighting/illuminated signs to be flashed rapidly to warn.