From my observation observations (since I've haven't had the opportunity to design a plane crash yet), a plane crash or other large scale impact is designed with a ton of carefully layered sounds/events. I've always liked this one. Which is less about the impact and more about the aftermath. Really nice use of metal, water in this sequence to elevate the danger.
Real world props.
I'd suggest finding a large metal dumpster or shipping container to start. They can sound huge if recorded in the right way.
It's not always necessary to pitch elements down to sound big if you record them with some proximity effect. Or the opposite, use acoustics to your advantage and record with some distance to capture some nice big reverb/slap. Contact mics are also your friend, especially with metal. And don't forget about the subwoofer, a key tool in designing these large scale events. A little 60kHz rumble can go a long way in selling size.
Have you looked at library recordings of trains (rumble, wheel screeches), or car crashes? Building demolition? Those could make for nice material as well.