Biscuit74
Tucumseh will doubtless explain it much better than me but I think you may have misunderstood his point slightly. His point is not that the aircraft was not functioning correctly. It is more about the fact that it should not have been flying from a legal standpoint.
Think of it like driving without an MOT. Your car will function perfectly well without the certificate but if you were to crash, your insurance is completely invalid.
BV