# The Air Navigation Order 2016, Paragraph 5


In this Part—
“Airborne collision avoidance system” means an aeroplane system which—
(a)conforms to requirements prescribed for the purpose;
(b)is based on secondary surveillance radar equipment transponder signals;
(c)operates independently of ground based equipment; and
(d)is designed to provide advice and appropriate avoidance manoeuvres to the pilot in relation to other aeroplanes which are equipped with secondary surveillance radar and are in undue proximity;
“Automatic direction finding equipment” means radio navigation equipment which automatically indicates the bearing of any radio station transmitting the signals received by such equipment;
“Distance measuring equipment” means radio equipment capable of providing a continuous indication of the aircraft's distance from the appropriate aeronautical radio stations;
“Mode A” means replying to an interrogation from secondary surveillance radar units on the surface to elicit transponder replies for identity and surveillance with identity provided in the form of a four digit identity code;
“Mode C” means replying to an interrogation from secondary surveillance radar units on the surface to elicit transponder replies for automatic pressure-altitude transmission and surveillance;
“Secondary surveillance radar equipment” means such type of radio equipment as may be notified as being capable of—
(a)replying to an interrogation from secondary surveillance radar units on the surface; and
(b)being operated in accordance with such instructions as may be given to the aircraft by the appropriate air traffic control unit;
“VHF omni-range equipment” means radio navigation equipment capable of giving visual indications of bearings of the aircraft by means of signals received from very high frequency omni-directional radio ranges.

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Source: https://www.legislation.gov.uk/uksi/2016/765/schedule/6/part/2/paragraph/5 (the official version)
Page: https://openlegislation.uk/air-navigation-order-2016/schedule-6/part-2/paragraph-5
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.