Definition
An automated air traffic control radar function that alerts the controller when a tracked aircraft is observed, or predicted within a short look-ahead time, to be below or descending toward an altitude considered unsafe for terrain or obstructions in that area. When triggered, the controller issues a safety alert to the pilot.
Plain English
It is a computer warning inside ATC's radar system that flags up when an aircraft is getting too low for the terrain around it. The controller then calls the pilot to warn them.
Context Anchor
Seen in instrument flying and Tower En Route Control discussions, especially when ATC is providing radar-based services and monitoring aircraft altitude.
Why Pilots Care
Helps prevent controlled flight into terrain by giving controllers an early alert so they can advise the pilot.
Intuition Check
MSAW is not a cockpit warning generated by the aircraft. It is an ATC system alert that helps the controller notice a possible unsafe altitude.
Example Sentence 1
While descending into the valley, the pilot received a low altitude alert from the controller, triggered by the MSAW function.
Example Sentence 2
During the approach briefing the instructor explained how MSAW works as a backup safety net in instrument conditions.