I was in the cockpit on the ground stuck in a snow lock down back in the late 1970's It was an AA
727 and a certificate in the cockpit said this plane was leased by AA
from the Schroader Bank. (Spelling wrong) anyway the Capt. said the payments came out of the sales of the tix, and the bank got paid on a direct payment plan. After an allocated amount of time passed the A/L could simply hand the plane back and get a new one, or make a final payment and own it out right. The Idea was to have the plane in the service of the A/L for as little out lay as possible on a monthly basis, then fly the hell out of it and reap as much rev. as they can. Just like leasing a new Mercedes, taking all the tax breaks, then paying the risidule and keeping it and pumping more service out of it, or getting a shiney new one.