Definition
A radar altimeter test or sensitivity selector switch with three settings — HIGH, LOW, and OFF — used during preflight and approach checks. In the context of certain radar altimeter installations, selecting the wrong position (or leaving it OFF when it should be active) is a recognized operational error that can cause the radar altimeter to display incorrect height information or fail to provide a decision height alert during a precision approach.
Plain English
A switch with three positions on some radar altimeters. If the pilot leaves it in the wrong position, the altimeter may give a wrong reading or fail to warn the pilot at decision height.
Context Anchor
Seen on some aircraft audio panels or marker beacon controls during instrument approach setup, especially before flying an ILS approach.
Why Pilots Care
The wrong setting can produce missed marker signals or false indications that disrupt an approach.
Intuition Check
HIGH does not mean “better,” and LOW does not mean “worse.” Here they are sensitivity choices; OFF means the receiver will not provide its marker beacon indication.
Example Sentence 1
During the approach briefing, the pilot confirmed the HIGH/LOW/OFF three-position switch was set correctly so the radar altimeter would alert at decision height.
Example Sentence 2
Before starting the approach she placed the HIGH/LOW/OFF switch in HIGH for better reception at distance.