By David Learmount in London

General aviation aircraft of all kinds could be affected if a UK Civil Aviation Authority plan to mandate the carriage of Mode S elementary surveillance transponders within all UK airspace from 31 March 2008 is adopted. The CAA says its primary motivation for proposing the transponders is that more than half of all air-proximity events in UK airspace involve GA aircraft that cannot be detected by another aircraft’s airborne collision avoidance systems unless they have a transponder.

The CAA says: “Successful [Mode S] introduction will improve safety and will be an essential step towards managing the future increase in air traffic movements in the UK.” Unless something is done, the authority says, the rapidly increasing use of regional airports by airline traffic – which often requires commercial aircraft operating on instrument flight rules (IFR) flight plans to pass through uncontrolled airspace – the risk of collision would increase.

The CAA says it does not want to adopt the alternative of increasing the spread of controlled airspace, thus excluding GA or military aircraft operating under visual flight rules from larger areas of the UK’s skies. Mode S transponders also make GA aircraft visible to air traffic controllers using secondary radar (SSR), but they provide more information than just the location, identification and height presently available from Mode C.

The authority says: “Mode S enhanced surveillance [EHS] has been mandatory for all aircraft flying under IFR within notified Mode S airspace since 31 March 2005, with a two-year transition period until 31 March 2007.” If, after this consultation, the CAA were to decide to proceed, by the end of the transition period for the new rule – 31 March 2010 – all GA aircraft including gliders would be required to carry a Mode S transponder. The CAA says it is working with the aviation industry to develop a light-aviation SSR transponder and low-power SSR transponder that will meet the needs of specific sectors within GA, such as the gliding community.

Devices can be hand-held and battery-powered. The agency says it anticipates the cost of transponders will be between £500 ($940) and £1,000.

Source: Flight International