The most reliable bombers in the U.S. Air force are 94 40 year old B-52. The air force expects to keep 62 of them in service until 2044. The biggest maintenance problem with the B-52s are in its avionics. These are constantly being upgraded. The structural components are carefully and frequently inspected, with spare parts being obtained from B-52s previously taken out of service. No other combat aircraft has been kept in service so long, and its uncharted territory when it comes to do maintenance for such ancient airframes. But the B-52 is indispensable, as it can carry an enormous quantity of bombs and missiles to any place on the planet.