Definition
A turboprop engine in which the gas-producing turbine and the propeller are mechanically connected through a single, common shaft (with a reduction gearbox between them). Because the turbine and propeller are linked, changing engine power directly changes propeller rpm, and the propeller cannot turn independently of the engine's gas generator section.
Plain English
A turboprop where the spinning core of the engine and the propeller are tied together on the same shaft, so they always turn in step with each other. Speed up the engine and the propeller speeds up too — they cannot move separately.
Context Anchor
You may see this term when comparing turboprop engine designs, especially fixed-shaft engines versus free-turbine engines.
Derivation
"Fixed-shaft" describes the mechanical arrangement: the shaft is fixed (permanently linked) between the turbine and the propeller, as opposed to a free-turbine design where a separate turbine drives the propeller through its own independent shaft.
Why Pilots Care
The direct connection affects engine response to power changes, starting procedures, and propeller control during emergencies or feathering.
Intuition Check
“Fixed-shaft” does not mean the propeller blades are fixed in one angle, and it does not mean the engine has only one possible speed. It means the propeller drive is mechanically tied to the engine’s main rotating shaft.
Example Sentence 1
Because the trainer had a fixed-shaft turboprop engine, advancing the power lever increased both engine and propeller rpm at the same time.
Example Sentence 2
In training, the instructor explained how a fixed-shaft turboprop engine behaves differently during a simulated engine failure compared with a free-turbine model.