> I forgot why there are no parachutes on planes ? weight ?
There are parachutes on planes, as in whole airframe parachutes. Just not airliners. See Cirrus aircraft.
However, even in a Cirrus, you can only open the parachute within very specific parameters (altitude, airspeed and so on). Exceed these, and your parachute is worthless.
For obvious reasons, a whole frame parachute in a 737 is a crazy proposition. It is ridiculously heavy. Also, the plane flies much higher and much faster, so even if you COULD fit one made of some form of unobtanium, it would likely be useful only under very specific scenarios.
The other option would be to provide individual parachutes. Much like life vests.
Ok great. Let's assume they are small and can be stowed under the seat. How long would it take for a non-trained individual to put one of these on properly? Do they even have enough space to do it? How would they exit the plane? Most airliners don't have cargo-bay style doors. Exiting through the side doors is a bad idea. Who would inspect and repack hundreds of parachutes per plane?
The plane would have to be under controlled flight and slow enough for this to even have a chance to save any passengers. If you are in a slow and controlled flight, what use is this? Just land somewhere.
For ethiopian and lion air, it all happened so fast after takeoff that it is unlikely the pilots even had time to run their checklists. And we want to don parachutes on 100+ people and have them jump from an out of control plane?
> For obvious reasons, a whole frame parachute in a 737 is a crazy proposition. It is ridiculously heavy[...]
It's still crazy and impractical, but for what it's worth I think that's nobody's suggestion of how something like the Cirrus Airframe Parachute System would work on the scale of an airliner.
The mockups I could find of such proposed systems (e.g. [1] and [2]) all involve just the tube that forms the passenger cabin somehow ejecting as a whole and then parachuting to earth with some system similar to what was used for the Space Shuttle's solid rocket boosters[3], maybe with added retro-rockets for the landing.
You could also imagine a system where each passenger is sitting in an ejection seat taken from a B-2 or F-35. The cost would be insane, but it could be done.
I'd pay a premium to have my own emergency wingsuit..