Mike is correct, they do use retreads. Not sure if all tires on a commercial jet can be, or if some must be new. But having known several commercial
jet mechanics in my life ( usually drinking buddies ), I have seen a lot of accident reports where damage to the undercarriage was caused by an
exploding tire. The official accident report (French version) on the Concord was that it ran over a metal strip dropped from the plane that had left
just before it. The tire shredded, but also picked up the metal piece which was most likely the piece that punctured the fuel cell. The fire was blamed
mostly on the tank wall being too thin, as well as the rubber lining too thin to seal the puncture. Our NTSB report said the real damage was from the
tire and steel bead.
I have a cousin, my Dad's nephew, who was in the Navy at the end of Viet Nam. He was stationed on the Nimitz, and has lots of stories of fighters coming
in to land. One I found especially funny was a jet jockey slammed in blowing both tires on the main gear. He missed the wires and bolted. Someone made
the decision that the jet would do less damage to the flight deck if it bellied in instead of coming in gear down. Of course, the arresting gear won't work that
way, but they were hoping it might snag a wire, or at least grind to a halt on it's own. It didn't. It spun 180 degrees and slid off the deck *** first. They saved
the pilot, but didn't bother salvaging the jet.