All powered international flights using UK airspace will have to carry and operate Mode S transponders under new proposals to expand Mode S usage.

Britain's Civil Aviation Authority says it does not plan to require all aircraft to fit Mode S in all UK airspace, but changes agreed following consultation would come into force on 31 March next year.

The CAA argues that all aircraft in controlled airspace must be visible to air traffic control and to the airborne collision avoidance systems of other aircraft, which entails mandating Mode S carriage in controlled airspace.

This "phase two" proposal would take the transponder policy one step beyond the existing "phase one" rule - effective from 31 March this year - when only Mode S transponders will be acceptable in any of the UK airspace where transponders are mandatory, although aircraft already fitted with traditional Mode A/C equipment will be given until 31 March 2012 to upgrade.

The CAA says it is keen "to meet the concerns of the general aviation community about the cost and technical challenges of the wider use of Mode S", so it proposes a phased introduction of phase two.

Apart from mandating the carriage of Mode S in all UK-controlled airspace, the proposals include: implementing a process to consider applications for "transponder mandatory zones" (TMZs) outside controlled airspace including gliders in the SSR transponder carriage regulations and mandating the carriage and operation of Mode S transponders on all powered aircraft conducting international flights, to comply with international standards.

GA aircraft that cannot equip with Mode S transponders by 31 March 2009 will not be grounded, the CAA insists, but it warns: "Aircraft that are not equipped with transponders may find it difficult to get ATC clearance to enter certain airspace."

The consultation closes on 31 May 2008.

BLOB: A Deutsche Lufthansa Boeing 737 flying between Frankfurt and Munich on 18 January became the first-ever aircraft to be identified by having its Mode S transponder-transmitted flight identity automatically correlated with flight plan data held by air traffic control, according to Eurocontrol.

John Law, Eurocontrol Mode S programme manager, says the success of this first flight paves the way for expanded city-pair flights based on Mode S flight identity, to be inaugurated by the Deutshe Flugsicherung, the German air navigation service provider, this year.