·First the cost would be too much.
·Second the airplane wouldn't fly, it would be too heavy to get off the ground.
·Third the Black Boxes aren't black, they are orange, and they aren't indestructible, the NTSB has to salvage them often. They aren't even water tight, but since they use a steel tape it will survive immersion.
You reach the point of dimensioning returns, with the stronger you build a plane, the more weight you put on it, which requires larger engines, which will require more fuel, which will require more storage space, which will require a stronger airplane…
A plane has to be built as light as possible for it to fly. Aluminum has come into use in the aircraft industry because for the weight it is a very strong material that is also why it is popular in the automobile industry. My dad worked for Boeing and said that the girder design had to have lightening holes in it. Of course anyone who heard that would think of a lightning strike. The holes are required to make it lighter, and because of a quirk in statics and dynamics of the girder the strength of that girder is NOT reduced by the holes in it.
I watched the movie The Guardian tonight and they stated that a fall from as little as 50' is like hitting concrete when you hit the water. So how do you design something that can fall from 20,000 feet at 200 mph, so it won’t break up on impact? If you built it out of solid iron or even one solid diamond then the passengers would still die because of the shock of impact.
Airplanes are designed to be as safe as possible and they are the safest way to travel. Most airline accidents only happen on takeoff and landing, but still you are flying a multi-ton vehicle with a heavy live load (the people) that is coming in at a high rate of speed. If that craft has an accident then people will die. That is unavoidable.
Airplanes have a glide path of less than 9 degrees when they come in to land. The space shuttle has a glide path of 45 degrees; another words it flies like a brick. Still they have to come in with empty onboard fuel tanks and the solid quartz windows had to be shaved to save weight. If you want it to fly then there is only so much structure it can carry. The same is true with cars, trains, motorcycles etc. They can all be made safer, but past a certain point they won’t work anymore because the weight of the structure is too great.
What you are proposing would be like trying to build cars with a foot of solid granite rock on each side. The car would move, but not more than 5 miles per hour. You certainly couldn't put it on the highway, and a plane designed like that wouldn't ever fly (Okay, the iron plane would be a little lighter, but it still wouldn’t fly.)