Originally Posted by
krismiler
For specialist roles such as engine test platforms and fire bombing, where utilisation is very low, an obsolete aircraft such as a B747SP or DC10 costing a few hundred thousand dollars is ideal as the higher fuel burn over the few hours it spends airborne is insignificant compared to the millions that would be tied up in a new model.
These can be real residual operations where you cannot get hull insurance either - fire bombing, operation into unlicensed strips in remote areas, etc. This is why old piston-engined large aircraft lasted so long on such missions, notwithstanding Avgas cost, although they are pretty much all gone now. MEA at Beirut carried on with 707 operations long after everyone else for the same reason.