Definition
A turboprop engine design in which the gas-generator section and the propeller-driving turbine are mounted on separate, mechanically independent shafts. The gas generator (compressor and its driving turbine) operates as one rotating assembly, while a second turbine — the power turbine — is driven only by the exhaust gas flow and turns the propeller through a reduction gearbox. There is no mechanical connection between the two shafts.
Plain English
A turboprop built with two separate spinning sections that are not physically connected. One section runs the engine and produces hot gas. That hot gas then spins a second, independent section that turns the propeller. Because they are not linked by a shaft, each can spin at its own speed.
Context Anchor
Seen when studying turboprop engine types, especially under split-shaft or free turbine engine descriptions.
Derivation
Split simply means divided into separate parts, and shaft refers to the rotating rod that transmits power inside an engine. The name describes the design directly: the engine's rotating power path is split into two independent shafts rather than one continuous shaft.
Why Pilots Care
In a split-shaft design the propeller is not mechanically tied to the gas generator, so the propeller can be feathered or stopped on the ground while the engine keeps running. It also means the gas generator and propeller can run at their own most efficient speeds, which affects how power is set and how the engine responds to throttle inputs.
Intuition Check
Do not read “split-shaft” as a broken or cracked shaft. It means the engine is designed with separate rotating shafts that are not mechanically locked together.
Example Sentence 1
Because the airplane has a split-shaft engine, the pilot could feather the propeller during the emergency drill while the gas generator continued to run.
Example Sentence 2
During shutdown the pilot noted the split-shaft engine allowed the propeller to stop independently once the power turbine lost drive.