Parabellum - the Mags will accept a guilty plea and decide whether their powers are sufficient to sentence. If not it'll be committed to crown court for sentencing only. If it's a not guilty plea, it may be deemed not suitable for summary trial and sent to crown.
Basil - not sure if the below is relevant to your earlier point:
Activities Ancillary to Aviation Functions
94(3) For the purposes of sections 92 to 102 of this Act, a reference to an activity which is ancillary to an aviation function is a reference to anything which falls to be treated as such by virtue of subsections (4) to (6) below.
94(4) An activity shall be treated as ancillary to an aviation function if it is undertaken-
(a) by a person who has reported for a period of duty in respect of the function, and
(b) as a requirement of, for the purpose of or in connection with the performance of the function during that period of duty.
94(5) A person who in accordance with the terms of an employment or undertaking holds himself ready to perform an aviation function if called upon shall be treated as carrying out an activity ancillary to the function.
94(6) Where a person sets out to perform an aviation function, anything which he does by way of preparing to perform the function shall be treated as an activity ancillary to it.
94(7) For the purposes of this sections it is immaterial whether a person performs a function or carries out an activity in the course of an employment or trade or otherwise.
94(5) and 94(6) cover pre-flight stuff etc I believe - sorry if this was totally irrelevant as I've simply skimmed over the replies.