Learn how turboprop autothrottle controls airspeed and torque, how it differs from prop governing, and why many turboprops do not have it.
In turboprop aircraft, autothrottle automatically adjusts engine power to hold a selected airspeed or power target. It commands the power levers—or an electronic engine-control equivalent—while the propeller governor manages blade angle and propeller RPM. The autopilot still controls pitch, and the exact division of duties varies by aircraft.
In our Aviation & Real-World Flying coverage, the essential caveat is that many turboprops have no autothrottle at all. FADEC, constant-speed governing, autofeather and automatic take-off power control can all automate part of the powerplant without providing automatic speed control.
What does turboprop autothrottle actually control?
A turboprop autothrottle controls commanded engine power, not necessarily every lever on the throttle quadrant.
With conventional controls, the power lever requests engine output, the propeller lever selects governed RPM, and the condition lever handles functions such as fuel cut-off and idle selection. Integrated single-lever installations may coordinate fuel flow, propeller RPM and blade angle electronically.
- Select a target: The pilot or flight-management system selects an airspeed, torque value or take-off/climb power schedule.
- Measure the result: The system monitors airspeed and relevant engine data, which may include torque, temperature, gas-generator speed and propeller RPM.
- Command power: A servo moves the physical power lever, or a full-authority digital engine control receives an electronic power request.
- Apply limits: The controller restricts its command according to the aircraft's operating logic and announces its active, armed or disconnected state.
Automatic operation normally stays within the forward-flight power range. Ground beta and reverse are generally selected manually, although retard and inhibit logic differ between aircraft.
Autothrottle, prop governing and FADEC are not the same
Each system controls a different part of turboprop operation, even when several are integrated behind one power lever.
| System | Main job | What it does not guarantee |
|---|---|---|
| Autothrottle or autopower | Changes commanded power to maintain airspeed or a selected power schedule | Maintaining the target after an engine or flight-envelope limit is reached |
| Propeller governor | Changes blade angle to hold selected propeller RPM | Controlling aircraft airspeed |
| FADEC or electronic engine control | Meters fuel, schedules engine operation and applies designed protections | Autothrottle capability unless that function is specifically installed |
| Autofeather or ATPCS | On equipped aircraft, responds to a qualifying engine failure with propeller feathering and/or power uptrim | Routine airspeed control |
How does it hold airspeed without changing propeller RPM?
In speed mode, the system raises or lowers shaft power while the propeller governor keeps RPM near its selected value.
Adding fuel increases gas-generator output and turbine torque. The governor then coarsens the propeller blades so they absorb the additional power without a matching increase in RPM. This separation between engine output and propeller speed is central to understanding how turbine engines deliver shaft power.
- IAS or speed mode: Autothrottle changes power to hold the selected speed while the autopilot controls altitude or flight path with pitch.
- Torque or power mode: Autothrottle maintains a commanded power setting; it does not necessarily hold airspeed.
- Flight-level-change or climb mode: The system may hold scheduled climb power while the autopilot uses pitch to control speed.
The flight-mode annunciator therefore matters more than visible lever movement. The control-loop principle resembles autothrottle operation in jet airliners, but the turboprop also has a propeller governor, shaft-torque limits and slower interacting engine and propeller responses.
Does every turboprop have autothrottle?
No; many transport, utility and older turboprop aircraft require the pilot to set power manually throughout the flight.
Do not assume that FADEC, a torque limiter or an autofeather system provides autothrottle. If the aircraft documentation describes only power management or engine-failure uptrim, it may still lack any system capable of holding a selected airspeed.
Lever movement is not a reliable test either. Servo-driven systems may move the cockpit lever, while electronically integrated systems may change commanded power without back-driving it. The aircraft manual and flight-mode annunciations are the deciding references.
What happens when autothrottle reaches an engine limit?
Autothrottle cannot maintain an impossible target once it reaches maximum permitted power or flight idle.
In a climb, airspeed may decay if the requested speed and climb rate demand more power than is available. During a steep descent, speed may rise even with the power at idle. Depending on the aircraft and conditions, the active ceiling may be torque, inter-turbine or turbine-gas temperature, gas-generator speed, propeller RPM or another manufacturer-defined limit.
The pilot must recognise the limit and change the flight path, vertical rate or selected mode. Autothrottle reduces workload; it does not remove responsibility for monitoring airspeed and engine indications.
Why does turboprop autothrottle misbehave in a simulator?
In a simulator, most apparent autothrottle faults come from mode misunderstandings, hardware-axis conflicts or an aircraft that does not model the feature.
- Verify the capability: Check the simulated aircraft's documentation rather than assuming every turboprop has autothrottle.
- Read the annunciation: Confirm that the mode is active rather than merely armed, and distinguish speed mode from torque or power mode.
- Remove axis conflicts: A mistake we see constantly is treating the propeller axis as a second throttle. Remove duplicate bindings, calibrate noisy controls and review the separate power, propeller and condition-lever functions. An absolute hardware axis can repeatedly override a virtual lever moved by autothrottle.
- Allow for turboprop response: Gas-generator acceleration and propeller-governor movement introduce genuine lag. Our explanation of turboprop lag and high-RPM indications in X-Plane 12 covers the interaction in more detail. Persistent hunting, however, can indicate noisy hardware input, turbulence or incomplete aircraft-system modelling.
Before disconnecting in a simulator, match the physical throttle to the commanded or virtual position where the implementation permits. Otherwise, the simulator may snap to the hardware-axis position and produce an abrupt torque change.
How should you take over from autothrottle?
Disconnect autothrottle with the aircraft's designated control, confirm that it is disengaged, and set power manually while monitoring airspeed, torque and temperature.
- Use the proper disconnect control rather than forcing the power lever against a powered servo.
- Check the annunciation and warning so an armed or re-engaged mode is not mistaken for manual control.
- Set and monitor manual power using the aircraft's normal torque and temperature limits.
Autothrottle and autopilot are separate systems, so disconnecting one does not necessarily disconnect the other. In a real aircraft, the approved flight manual, operating handbook and abnormal checklist take precedence because alert cancellation, lever synchronisation and re-engagement logic vary by installation.