Pressure-altitude reporting transponder
109.  An AOC holder must ensure that every large aeroplane is equipped with a pressure‑altitude reporting transponder —
(a)which operates in accordance with the provisions of Volume IV of Annex 10 of 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 airborne or on‑the‑ground status of the aeroplane when that aeroplane is equipped with an automatic means of detecting such status.