Definition
An autopilot mode that automatically maintains the aircraft at the pressure altitude existing at the moment the mode is engaged. The autopilot commands pitch inputs as needed to keep that altitude steady, regardless of small changes in airspeed, power, or configuration.
Plain English
A button or mode on the autopilot that tells the airplane, 'Stay at the height you're at right now.' Once you press it, the autopilot flies the pitch for you to keep the airplane level at that altitude.
Context Anchor
Seen on an autopilot control panel or flight display when managing altitude during instrument flight.
Why Pilots Care
It reduces workload and prevents altitude deviations during prolonged level flight.
Intuition Check
ALT HOLD does not mean the airplane will automatically go to any altitude you have in mind. It means the autopilot is trying to keep the airplane at the altitude it has been told to hold.
Example Sentence 1
Level at 6,000 feet, the pilot engaged ALT HOLD and began setting up the approach briefing.
Example Sentence 2
With ALT HOLD engaged the aircraft stayed at 8000 feet while the pilot reviewed the arrival procedure.