. The portion of a runway, beyond the threshold, where it is intended landing aircraft first contact the runway [ICAO]. As it relates to fixed-wing aircraft, it is the first 3000 ft (900 m) of the runway beginning at the threshold. It is the area where the fixed-wing aircraft are expected to touch down. The area is used for determining the touchdown zone elevation in the development of straight-in landing minimums for instrument approaches. A touchdown zone marking consists of pairs of rectangular markings symmetrically disposed about the centerline. The number of pairs is dependent on the length of the runway. It is one pair for runway lengths less than 3000 ft (900 m), two when the length is 3000 up to 4000 ft (900 up to 1200 m), three pairs when the length is 4000 up to 5000 ft (1200 up to 1500 m), four when it is 5000 up to 7000 ft (1500 up to 2100 m), and six if the length is 7000 ft (2100 m) or more. The system of lighting in the touchdown zone area consists of two rows of transverse light bars located symmetrically about the runway centerline. The basic system commences at 100 ft from the landing threshold and extends to 3000 ft from the threshold or the midpoint of the runway, whichever is the lesser.ii
. For rotary wings and vectored thrust aircraft, the touchdown zone is that portion of the helicopter landing area or runway used for landing.