Some aircraft need efficiency at moderate speeds, not raw jet thrust. The turboprop combines a jet engine core with a propeller. The turbine drives a gearbox, the gearbox turns the propeller, and the propeller produces most of the thrust.

Regional airliners, military transports, and agricultural aircraft use turboprops because they burn less fuel than jets at lower altitudes and speeds. They also perform better on short runways.

Advantages and limits

• Efficient at speeds below about 700 km per hour
• Strong takeoff performance on short fields
• Propeller tips limit maximum speed
• Noisy compared to turbofans

The gearbox is a critical component. It reduces the turbine's high RPM to a speed the propeller can handle without the tips going supersonic. Gearbox failures are rare but serious when they occur.