[MBCook]

Oh I agree. The idea of forgetting to secure a tire, even without knowing the aviation specific bits, is clearly a HUGE mistake.

But I just don’t see any other way this could happen unless the tire was secured and just that part of the axle broke off which seems incredible unlikely in general, let alone compared to human fallibility.

[Zigurd]

Axles have failed on landing gear, but the wheels on both sides would be affected. The images I have seen of examples are all due to hard landings.