Definition
A ground-based visual glide path aid, installed beside the runway, that uses a single light source whose color and pulsing behavior tell the pilot whether the aircraft is on, above, or below the correct approach slope. A steady white light indicates on glide path; a steady red light indicates slightly below; a pulsing red light indicates well below; and a pulsing white light indicates above the glide path.
Plain English
A single light next to the runway that changes color and flashes to show if you are flying down to the runway at the right angle, too high, or too low.
Context Anchor
Seen on airport information, approach chart airport sketches, and during the visual part of an approach to a runway equipped with this lighting system.
Derivation
‘Pulsating’ comes from the Latin ‘pulsare,’ meaning to beat or throb — describing the flashing behavior of the light. It helps because the pulsing itself carries meaning: a steady light means you are on or near the correct path, while a pulsing light is the system telling you something is off.
Why Pilots Care
Provides immediate visual guidance to maintain a safe descent angle and avoid landing short or floating long.
Grounding Statement
As you fly toward the runway, the PVASI indication changes as your height changes relative to the intended path.
Intuition Check
Do not read PVASI as lateral guidance. It helps with vertical path to the runway, not left-right alignment.
Example Sentence 1
On short final, the PVASI showed a steady white light, confirming the aircraft was on the correct glide path to the runway.
Example Sentence 2
On the RNAV approach chart, the PVASI symbol indicated the system was available for the visual portion of the arrival.