Definition
An airport surface sign that has a yellow background with a black inscription depicting the runway holding-position marking. It is located on the runway side of the holding-position marking and is used by a pilot exiting the runway to identify when the aircraft has fully crossed the marking and is clear of the runway.
Plain English
A yellow sign next to the painted hold line on a taxiway. When you can see this sign behind you after exiting a runway, your whole airplane is off the runway.
Context Anchor
Seen while exiting a runway after landing, usually near the pavement marking with two solid lines and two dashed lines.
Derivation
Boundary comes from bound, meaning a limit or edge. That helps here because the sign marks the limit of the runway area, not the physical end of the pavement.
Why Pilots Care
Clearly marks pavement limits to prevent runway incursions and maintain safe separation from active surfaces.
Intuition Check
Do not read “boundary” as the end of the runway pavement. Here it means the protected edge of the runway area that aircraft must clear after landing or crossing.
Example Sentence 1
After landing and turning off at taxiway B, the captain continued forward until the runway boundary sign was behind the aircraft before reporting clear of the runway.
Example Sentence 2
During night operations, runway boundary signs helped the crew maintain awareness of where the runway ended.