Definition
A turboprop engine design in which the propeller, the reduction gearbox, and the engine's gas-producing turbine are all connected to a single, common shaft, so that they all rotate together as one mechanical unit. Engine power output is changed by altering the fuel flow and the propeller blade angle, which together change the load on the shaft and therefore the engine's RPM and torque.
Plain English
A turboprop layout where the propeller and the spinning parts inside the engine are all linked on one shaft, so they always turn together. When the engine spins faster, the propeller spins faster too — they can't move independently.
Context Anchor
Seen in turboprop engine discussions, especially when comparing fixed-shaft engines with free-turbine turboprop engines.
Derivation
Fixed' here means rigidly connected, not 'unable to move.' The shaft is 'fixed' in the sense that the propeller and turbine are locked together on it, so neither can spin independently of the other.
Why Pilots Care
The pilot must coordinate power and propeller controls as a single system; any change in engine speed immediately changes propeller speed and thrust.
Intuition Check
Do not read fixed as motionless. In fixed-shaft, the shaft still rotates; fixed means the engine and propeller drive are mechanically linked instead of free to spin separately.
Example Sentence 1
In a fixed-shaft turboprop, advancing the power lever increases fuel flow and the entire shaft — turbine and propeller together — speeds up.
Example Sentence 2
During the preflight, the instructor explained that feathering the propeller on this fixed-shaft engine also stops the power turbine from turning.