Planes are mostly filled with empty space. The fuel is in two tanks in the fat parts of the wings. In a catastrophic plane crash, at top speed say, maximum destruction, the majority of that fuel burns off in the fireball resulting from crash impact. Fires are then prolonged by whatever other "fuel" is present at the location of the crash which was set alight by it - for example the wreckage of the plane itself and the matter it crashed into. The flammability of that material, and access to oxygen, would be the determining factors as to how long that fire would last.
Planes are mostly filled with empty space. The fuel is in two tanks in the fat parts of the wings. In a catastrophic plane crash, at top speed say, maximum destruction, the majority of that fuel burns off in the fireball resulting from crash impact. Fires are then prolonged by whatever other "fuel" is present at the location of the crash which was set alight by it - for example the wreckage of the plane itself and the matter it crashed into. The flammability of that material, and access to oxygen, would be the determining factors as to how long that fire would last.