Air passenger duty (APD) is calculated on the number of passengers on board a flight on its take off from a UK airport. No tax is due on flights without passengers.
Exemptions apply for certain categories of passengers, including cabin crew and children under two who are not allocated their own seat. Flights that depart from an airport in the Scottish Highlands and Islands are also exempt.
Aircraft certified as having an authorised take off weight of less than 10 tonnes, or that are equipped to carry fewer than 20 passengers, are outside the scope of the tax, and consequently not liable to air passenger duty. We cannot say how many aircraft are outside the scope of APD; however, the Civil Aviation Authority publishes details of UK registered aircraft at:
http://www.caa.co.uk/default.aspx?catid=56&pagetype=90&pageid=107
We do not have information on how many aircraft are privately-owned.