polzin,
Addtionally to your responce to 5y744
When Delta could not buy the ATA TriStar's they picked up 10 ex-Eastern L-1011's. The majority of these were in "rough" shape and Delta still thought that they were worth the extra maintenance costs. Remember, it was not until Delta had removed the TriStar's from service that they started to have revenue problems, that ultimately lead to their bankruptcy.
A couple of other airliners Air Transat and LTU have both publicly stated they owe their existance to the proffits they generated while operating the TriStar.