Pressure-altitude reporting transponder
109.—(1)  An AOC holder must ensure that every small aeroplane is equipped with a pressure‑altitude reporting transponder —
(a)which operates in accordance with the provisions of Volume IV of Annex 10 to the Chicago Convention;
(b)which is capable of operating in Mode S;
(c)which has a data source that provides pressure‑altitude information with a resolution of 7.62 m (25 ft) or better; and
(d)which is provided with an airborne or on‑the‑ground status of the aeroplane when that aeroplane is equipped with an automatic means of detecting such status.
(2)  An AOC holder must ensure that every helicopter is equipped with a pressure‑altitude reporting transponder which operates in accordance with the provisions of Volume IV of Annex 10 to the Chicago Convention.