Definition
A turboprop engine fuel-metering system that uses engine air pressures, sensed pneumatically, to schedule fuel flow to the combustion section. Pressure signals from the compressor and other engine stations act on diaphragms and bellows inside the fuel control unit, which then mechanically meters the correct amount of fuel for the engine's operating condition.
Plain English
A fuel control that decides how much fuel to send to the engine by sensing air pressures inside the engine, rather than by electronic computation.
Context Anchor
Seen in turboprop engine discussions, especially when describing how a split-shaft or free turbine engine controls fuel flow as power demand changes.
Derivation
Pneumatic comes from the Greek pneuma, meaning breath or air. The name reflects that the system uses air pressure, not electronics, to do the thinking and metering.
Why Pilots Care
It maintains correct fuel flow during rapid power changes, protecting the engine from damage or flameout.
Analogy
It is like a thermostat that adjusts heat based on the temperature it senses. In this case, the fuel control adjusts fuel based partly on the air pressure it senses inside the engine.
Intuition Check
Pneumatic does not mean air is mixed into the fuel or that the engine is powered by air. Here it means air pressure is being used as a signal to help control fuel flow.
Example Sentence 1
The PT6's pneumatic fuel control system meters fuel based on compressor discharge pressure and pilot power lever position.
Example Sentence 2
On engine start the pneumatic fuel control system limits fuel until compressor airflow is sufficient to prevent a hot start.