The US Air Force has decided that it will retain the TF33 engines on its B-52H heavy bombers until they are retired in 2040. The aircraft and engines will be 80 years old at that point. The TF33 is extremely reliable and is used by the E-3A, E-8C, C-141B, and KC-135E. The Air Force has, several times, looked at the concept of buying new engines, based on the theory that newer engines might burn less fuel. The problem is that the relatively simple T33 is easy to maintain, while newer more efficient engines are expensive to buy and harder than the T33 to maintain.Stephen V Cole