Definition
A visual illusion on approach in which a runway that is narrower than the pilot is accustomed to creates the impression that the aircraft is higher than it actually is, and a runway that is wider than usual creates the impression that the aircraft is lower than it actually is. Acting on the narrower-runway illusion typically leads the pilot to fly a lower-than-normal approach, with a risk of striking obstacles or landing short. Acting on the wider-runway illusion typically leads to a higher-than-normal approach, a late or hard landing, or overshooting the runway.
Plain English
Your eyes use the width of the runway to judge how high you are. A narrow runway looks far away, so you feel too high and tend to descend too low. A wide runway looks close, so you feel too low and tend to stay too high. Both feelings are wrong.
Context Anchor
Encountered during visual approaches and landings, especially at an unfamiliar airport or any runway that looks noticeably wider or narrower than the runways a pilot normally uses.
Derivation
“Illusion” comes from a Latin word meaning “to mock” or “to deceive.” That helps here because the runway itself has not changed your height; the picture your eyes are giving you is deceptive.
Why Pilots Care
Failure to recognize the illusion can result in a low approach, landing short of the runway, or an unstabilized approach.
Grounding Statement
The runway picture in the windshield can make your height feel wrong even when the aircraft is actually on the correct path.
Intuition Check
Do not assume the runway’s width only affects side-to-side spacing. In this context, runway width can change how high or low you think you are during the landing approach.
Example Sentence 1
Briefing the approach into the unfamiliar field, the captain reminded the first officer that the runway was noticeably narrower than their home base, so they should expect a runway width illusion making them feel higher than they really were.
Example Sentence 2
On the wide runway the pilot recognized the opposite width illusion and maintained altitude until the proper visual reference was reached.