Definition
The height of the straight-line descent path of an instrument approach, or the visual glide path on a precision approach, above the runway threshold. On an ILS or visual glide path system such as VASI or PAPI, the TCH is published or designed so that an aircraft on the correct glide path will cross the runway threshold at that specified height above the ground.
Plain English
How high the aircraft will be above the start of the runway if it stays exactly on the published glide path during landing.
Context Anchor
Seen on instrument approach information and glide path guidance for landing.
Derivation
Threshold here means the beginning of the usable landing surface of the runway, not a generic 'starting point.' Crossing Height simply means the height at which the aircraft passes over that point. Together: how high above the runway threshold the aircraft is when it crosses it.
Why Pilots Care
It confirms the aircraft is on the correct glide path to clear obstacles and touch down at the proper point on the runway.
Intuition Check
Threshold Crossing Height is not the height where the airplane touches down. It is the height over the runway threshold while still descending toward the landing area.
Example Sentence 1
The approach chart showed a TCH of 50 feet, so the pilot expected to cross the runway threshold 50 feet above the ground if she stayed on the glide path.
Example Sentence 2
If you stay on the glide slope, you will cross the threshold at the published height and land in the touchdown zone.