Uncle Ian – (U.K only.) You will find in the Flight Manual Supplement the category in which the mount has been certified. For example the Wescam film system on the AS 355/350 is certified for Aerial Work. If you fit a Tyler Major mount to an AS 355 it is certified under Transport Category. (Passenger.) Therefore if the Tyler was fitted the aircraft remains in the Transport category. (No problem, nothing to do) If you have fitted the Wescam the aircraft has been downgraded to Aerial work. You then have to go a bit deeper into the A.N.O. and see that exemptions from Articles 8(1) and 9(2) are required. (How sad I am I for knowing this?) The wording in the exemption issued by the CAA (once you have asked for it) will bring the aircraft back up to Public Transport category with the mount fitted. This then covers you to operate with passengers, ie. Director, producer and all the others who want to get in the way of you carrying some extra fuel before the sun disappears behind the clouds.