Ask @dna_977:

Why is there a life jacket under the seat on an airplane, but not a parachute?

Opening the door of the plane is not a good idea; because of the pressure difference people will pull out to the air, and if you only had parachute what would you do if you landed on the ocean? also if you dont have oxygen mask you will balckout in minutes, your probability to stay alive with life jacket maybe more than your life probability with parachute; also most of the people hadn't tried how use the parachute.

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