Definition
A category of autopilot system that controls the aircraft by sensing and responding to rates of change — primarily turn rate, roll rate, and pitch rate — rather than to fixed attitude references. Rate-based autopilots typically use turn coordinator or rate gyro inputs to keep the aircraft wings-level or to hold a commanded turn rate, and they make corrections proportional to how fast the aircraft is departing from the desired flight path.
Plain English
An autopilot that flies the aircraft by measuring how quickly it is turning, rolling, or pitching, and then correcting based on those rates of movement.
Context Anchor
Seen in discussions of autopilot design, especially when comparing simpler autopilots with systems that use a full attitude reference.
Derivation
‘Rate’ here means rate of change — how fast something is moving or changing per second. The system is ‘based’ on those rates as its primary reference, as opposed to attitude-based systems that reference pitch and bank angles directly.
Why Pilots Care
Rate-based autopilots respond more slowly than attitude-based systems and can struggle in turbulence, because they only react after movement has already begun. Knowing your autopilot is rate-based helps you set realistic expectations for how tightly it will hold heading and wings-level, especially in bumpy air.
Intuition Check
Do not read rate based as meaning based on airspeed or engine power. Here, rate means how quickly the airplane is turning, rolling, or otherwise changing its motion.
Example Sentence 1
Because the aircraft had a rate-based autopilot, the pilot noticed it took a moment to correct heading deviations in light turbulence.
Example Sentence 2
Older trainers often used rate based autopilots that responded only to how fast the nose was pitching up or down.