Definition
The height of the straight-line descent path of an instrument approach (such as an ILS glideslope or a published vertical guidance path) above the runway threshold, expressed in feet. It is the point at which a properly flown approach path crosses directly over the beginning of the usable runway surface.
Plain English
How high above the start of the runway you'll be if you fly the approach exactly as designed. For most ILS approaches, this is around 50 feet.
Context Anchor
Seen on instrument approach information and runway landing data, especially where a published descent path leads the aircraft toward the runway.
Derivation
Threshold refers to the marked entrance of the usable runway surface; crossing height is the altitude at which the aircraft passes over that entrance point.
Why Pilots Care
It confirms proper obstacle clearance and a safe touchdown point on instrument approaches.
Grounding Statement
Picture the airplane descending toward the runway and crossing the runway’s starting edge at about the published height.
Intuition Check
Do not read “threshold” as a general limit or decision point here. In TCH, the threshold is the marked beginning of the usable runway for landing.
Example Sentence 1
The approach plate showed a TCH of 55 feet, so we knew the glideslope would put us just above the threshold before flare.
Example Sentence 2
Staying on glide slope keeps the aircraft at the published TCH when crossing the threshold.