Definition
A radio advisory issued by an air traffic controller when an aircraft's observed altitude, as shown on the controller's radar display, is below or is predicted to descend below a published or assigned safe altitude. The phrase alerts the pilot that immediate verification of altitude is required, and, where applicable, the controller will state the minimum safe altitude (MSA) for the area.
Plain English
A controller is telling you that your aircraft looks too low on their radar and that you need to check your altimeter and climb if necessary. It is a safety warning, not a routine call.
Context Anchor
Heard as an urgent radio call from air traffic control, often while receiving radar service during arrival, departure, approach, or flight near terrain or obstacles.
Derivation
“Altitude” comes from a Latin word meaning “height.” In this phrase, it means the aircraft’s height in relation to a safe reference, not just a number on an instrument.
Why Pilots Care
The alert prevents controlled flight into terrain by prompting immediate corrective climb before the situation becomes critical.
Intuition Check
Do not treat this as a routine altitude reminder. It is an urgent safety warning that the aircraft may be too low for its location.
Example Sentence 1
Approach called, 'Cessna Three-Four-Alpha, low altitude alert, check your altitude immediately, the MSA in your area is four thousand five hundred,' and the pilot promptly initiated a climb.
Example Sentence 2
After receiving 'Low Altitude Alert, Check Your Altitude Immediately,' the crew confirmed their climb and reported reaching the assigned altitude.