Ground proximity warning system
120.—(1)  An AOC holder must ensure that every relevant aircraft that corresponds to one of the following descriptions is equipped with a ground proximity warning system which has a forward looking terrain avoidance function:
(a)a turbine-powered aeroplane with an MCTOM exceeding 5,700 kg, or with an MAPSC exceeding 9;
(b)a turbine-powered aeroplane with an MCTOM not exceeding 5,700 kg and an MAPSC exceeding 5 but not exceeding 9;
(c)a piston-engined aeroplane with an MCTOM exceeding 5,700 kg, or with an MAPSC exceeding 9;
(d)a helicopter with an MCTOM exceeding 3,175 kg, or with an MAPSC exceeding 9, and which is to be operated in accordance with the Instrument Flight Rules.
(2)  The ground proximity warning system required to be installed in an aeroplane described in paragraph (1)(a) —
(a)must provide an automatic and distinctive warning to the flight crew when the aeroplane is in potentially hazardous proximity to the earth’s surface; and
(b)must provide warnings for all of the following circumstances:
(i)excessive descent rate;
(ii)excessive terrain closure rate;
(iii)excessive altitude loss after take‑off or go‑around;
(iv)unsafe terrain clearance while not in the landing configuration:
(A)gear not locked down;
(B)flaps not in a landing position;
(v)excessive descent below the instrument glide path.
(3)  The ground proximity warning system required to be installed in an aeroplane described in paragraph (1)(b) or (c) —
(a)must provide an automatic and distinctive warning to the flight crew when the aeroplane is in potentially hazardous proximity to the earth’s surface; and
(b)must provide warnings for all of the following circumstances:
(i)excessive descent rate;
(ii)excessive altitude loss after take‑off or go‑around;
(iii)unsafe terrain clearance.