Definition
The cockpit indicator that shows the aircraft's vertical position relative to the published glide slope of an instrument landing system (ILS) or similar precision approach. The needle moves up when the aircraft is below the glide slope and down when above it, signaling the pilot to climb or descend to recapture the correct descent path.
Plain English
A pointer in the cockpit that tells the pilot whether the aircraft is too high, too low, or right on the correct downward path to the runway. If the needle is above center, fly up; if below center, fly down.
Context Anchor
Seen on an approach display during instrument approaches that give vertical guidance, including helicopter approaches to an airport or heliport.
Derivation
From 'glide slope' (the angled descent path to the runway) and 'needle' (a thin pointer on an instrument). The term reflects how the indicator was originally a literal mechanical needle that swung up or down to show vertical deviation.
Why Pilots Care
It allows the pilot to make small corrections and stay on the proper path for a safe landing in low visibility.
Intuition Check
Do not read “needle” as a physical needle in the aircraft. Here it means the displayed pointer that tells you where the aircraft is compared with the desired descent path.
Example Sentence 1
As the aircraft intercepted the final approach course, the glide slope needle began to center, confirming the start of the descent.
Example Sentence 2
When the glide slope needle drifted high, the pilot reduced power slightly to recapture the path.