You're mixing up a number of different, overlapping, complex issues, wnafly. The long-standing provision that approximates what you're probably after is section 30 of the Civil Aviation Act:
30 Weather etc. to be a defence
(1) In any proceedings for an offence against this Act or the regulations, it is a defence if the act or omission charged is established to have been due to extreme weather conditions or other unavoidable cause.
(2) Any defence established under subsection (1) need only be established on the balance of probabilities.
(And a hint to reduce the probabilities of you incurring the wrath of the moderators: If you start a thread that is effectively a question - the telltale clue is usually a question mark at the end of a sentence - it should probably be in the forum with 'Questions' in the name.)