Learn how turboprop autothrottle controls power, differs from the condition lever and prop governor, and behaves at limits or in a simulator.
In a turboprop aircraft, autothrottle—or autopower—automatically changes commanded engine power to maintain a selected airspeed or power target. It works through the power levers or electronic engine controls, while the propeller governor controls blade pitch and RPM. The condition lever normally remains a separate, manually selected control.
In our Aviation & Real-World Flying coverage, the crucial caveat is that many turboprops have no autothrottle. FADEC, autofeather, constant-speed propeller governing and automatic take-off power control can automate parts of the powerplant without providing automatic airspeed control.
What does autothrottle control in a turboprop aircraft?
Autothrottle controls the requested engine power, rather than directly controlling every propeller and engine function.
- Establish a target: The pilot or flight-management system selects an airspeed, torque setting or scheduled take-off, climb or cruise power.
- Measure the result: The controller monitors airspeed and relevant engine data, which may include torque, temperature, gas-generator speed and propeller RPM.
- Calculate a correction: If the measured value differs from the target, the system commands more or less power.
- Move or signal the power control: A servo may move the physical power levers, or an electronic system may send a power request to the engine controls without moving them.
- Respect installed limits: Depending on the design, limit logic constrains the command or warns the pilot. Autothrottle must not be assumed to protect every engine limit.
The cockpit control is normally called a power lever on a turboprop because it does more than meter fuel. In forward flight it requests power; in the ground range it may also command propeller beta and reverse blade angles. Our explanation of how turboprop engines produce and control shaft power covers the underlying engine arrangement.
| Control or system | Normal function | What it does not necessarily control |
|---|---|---|
| Power lever | Commands engine power in flight and, where designed, beta or reverse on the ground | Selected propeller RPM or fuel cut-off |
| Propeller lever | Selects governed propeller RPM on aircraft with a separate prop control | Aircraft airspeed |
| Condition lever | Selects functions such as fuel on/off, idle speed, feather or propeller RPM detents | Normal moment-to-moment power changes |
| Autothrottle or autopower | Changes the power command to meet a speed or power target | Every propeller, engine and flight-path function |
Does autothrottle control beta or reverse?
Autothrottle normally operates only within the forward-flight power range; pilots select ground beta and reverse manually.
The system may include ground-range inhibits or aircraft-specific retard logic, but that does not make beta or reverse part of routine speed control. Never force a powered lever into the ground range merely because the aircraft is fast on approach.
What does the condition lever do in a turboprop?
The condition lever configures the engine and propeller for a phase of operation; it is not another name for the throttle or power lever.
Its exact duties vary considerably. Depending on the aircraft, condition-lever positions may control fuel shut-off, start and feather, low or high idle, propeller feathering, or fixed propeller-RPM selections. Some turboprops have separate power, propeller and condition levers, while others combine propeller and condition functions or use a single electronically integrated lever.
During normal flight, autothrottle generally leaves the condition lever where the pilot has placed it. A wrong condition-lever setting can still produce unexpected propeller RPM, noise, response or available power, and autothrottle cannot correct an inappropriate fuel-cut-off, feather or idle selection.
How can autothrottle change power without changing propeller RPM?
Autothrottle changes engine torque while the propeller governor varies blade angle to keep RPM close to its selected value.
When more power is commanded, the engine supplies greater shaft torque. Without governing, that would tend to accelerate the propeller. The governor instead moves the blades towards a coarser pitch so that they absorb the extra power and create more thrust without a corresponding rise in RPM.
When power is reduced, the governor generally moves towards a finer blade angle to maintain RPM until it reaches an operating boundary. The relationship between blade pitch, RPM, airspeed and thrust is explained in our guide to how a variable-pitch aircraft propeller converts shaft power into thrust.
This separation is why a steady propeller-RPM indication does not mean autothrottle is doing nothing. Torque, fuel flow, blade angle and airspeed may all be changing while RPM remains governed.
Does every turboprop aircraft have auto throttle?
No; many turboprop aircraft require the pilot to set and monitor power manually throughout the flight.
FADEC is not proof that autothrottle is installed. FADEC schedules fuel and engine operation, while a propeller governor holds RPM. Autofeather and automatic power-uptrim systems deal with qualifying engine failures. None of those functions necessarily maintains a selected airspeed.
Power detents can also be misleading. Placing a lever in a climb or take-off detent may call up a predetermined power schedule without creating closed-loop speed control. The aircraft documentation, system controls and flight-mode annunciations are the reliable tests.
Should the power levers move by themselves?
Visible power-lever movement depends on whether the installation uses a mechanical servo or electronic power commands.
A servo-driven system back-drives the cockpit levers, making its changes obvious. An electronically integrated installation may alter commanded power without moving the levers. Lack of movement alone therefore proves neither engagement nor failure.
Does autothrottle or the autopilot control airspeed?
Either power or pitch may control airspeed, depending on the active vertical and autothrottle modes.
| Active mode or situation | Typical power function | Typical pitch function |
|---|---|---|
| Altitude or flight-path hold with speed mode | Autothrottle varies power to hold selected speed | Autopilot maintains altitude or flight path |
| Climb with scheduled climb power | Power system maintains a climb-power target | Autopilot varies pitch to hold speed |
| Torque or power mode | Autothrottle maintains selected torque or power | Airspeed depends on pitch, drag and available power |
| Manual pitch with speed mode | Autothrottle attempts to hold speed | Pilot controls the flight path |
These are common divisions rather than universal rules. The active flight-mode annunciation is more useful than watching lever movement. Our detailed explanation of how autopilot pitch and autothrottle divide airspeed control helps when a climb or descent appears to use the wrong control.
What happens when autothrottle reaches an engine or power limit?
Autothrottle cannot hold an impossible target after reaching maximum permitted power, minimum flight power or another system limit.
During a steep climb, airspeed can decay with maximum power already commanded. In a steep descent, speed can increase even at flight idle. Depending on the engine and installation, the limiting parameter may be torque, turbine temperature, gas-generator speed, propeller RPM or a manufacturer-defined power schedule.
The correct response is to change the flight path, vertical rate or selected target rather than waiting for more power that is unavailable. Underspeed and overspeed protection, where fitted, may command pitch, alter modes or disconnect automation, but their presence and authority vary by aircraft.
An engine failure adds another aircraft-specific case. Autofeather or automatic power uptrim may act on the failed and operating engines, but those protections are not ordinary autothrottle functions and do not guarantee that the selected speed will be maintained.
Why does turboprop autothrottle misbehave in a simulator?
Most apparent simulator autothrottle faults come from an incorrect mode, a conflicting hardware axis, a power limit or an aircraft that does not model the feature.
- Confirm that autothrottle exists: Check the simulated aircraft's documentation and cockpit controls. Do not infer it from FADEC, a power-management panel or a speed selector.
- Read the mode annunciation: Verify that speed or power control is active, not merely armed. In climb-power mode, pitch may be controlling speed while power remains fixed.
- Check all three control types: Make sure the power, propeller and condition controls are in the required ranges. Treating the propeller or condition axis as a second throttle is a mistake we see constantly.
- Remove axis conflicts: Look for duplicate throttle assignments, noisy potentiometers and separate controllers mapped to the same power axis. A continuously updating physical axis can override a virtual lever or repeatedly disconnect the automation.
- Check for a reached limit: If power is already at its permitted maximum or minimum, reduce the climb or descent demand rather than repeatedly reselecting autothrottle.
- Allow for engine response: Gas-generator acceleration, power-turbine response and propeller-governor movement introduce lag. Small corrections are normal; persistent hunting suggests turbulence, an unstable axis or simplified aircraft-system modelling.
Generic simulator bindings do not always correspond cleanly to a complex add-on's custom power and condition controls. This also explains why lever position is an unreliable substitute for engine indications: throttle position does not map directly to thrust in a flight simulator, especially when governors, detents and response lag are involved.
How should you disconnect and take over from autothrottle?
Use the designated disconnect control, confirm the disengagement indication and then set manual power while watching airspeed and engine limits.
- Synchronise simulator hardware where possible: Match the physical throttle quadrant to the commanded lever position before disconnecting, otherwise power may jump to the hardware-axis position.
- Use the proper disconnect: Do not force a cockpit lever against an active servo or rely on moving an unrelated propeller or condition control.
- Confirm the annunciation: Check that autothrottle is disengaged rather than armed for automatic re-engagement, and acknowledge any associated warning as specified for that aircraft.
- Set manual power: Monitor torque, temperature, propeller RPM and airspeed instead of copying the last lever angle.
Autothrottle and autopilot are separate systems, so disconnecting one does not necessarily disconnect the other. In real-world operation, the approved aircraft flight manual, operating handbook and abnormal checklist take precedence because disconnect warnings, lever synchronisation and re-engagement logic differ between installations.