17.—(1) Where required by the notified airspace being flown, aircraft must be equipped with a secondary surveillance radar transponder.
(2) In sub-paragraph (1), “secondary surveillance radar transponder” 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.