Definition
An aircraft propelled by the reaction force of a high-velocity jet of gas expelled rearward from an engine. The engine takes in air, compresses it, mixes it with fuel and burns it, then accelerates the resulting hot gases out through a nozzle. The forward thrust on the aircraft is the equal and opposite reaction to that rearward gas flow, in accordance with Newton's third law of motion.
Plain English
An aircraft pushed forward by shooting hot gas out the back of its engines. The harder the gas is thrown backward, the harder the aircraft is pushed forward.
Context Anchor
Seen in aircraft descriptions, operating limitations, performance discussions, and regulations that distinguish jet aircraft from propeller-driven aircraft.
Derivation
The word 'jet' comes from the French jeter, meaning 'to throw.' A jet-propelled aircraft is literally one that is propelled by something being thrown out the back -- in this case, a fast stream of hot gas.
Why Pilots Care
Jet propulsion determines aircraft speed, altitude capability, fuel consumption, and the specific procedures and ratings required for safe operation.
Intuition Check
Jet-propelled does not simply mean “fast.” It means the aircraft’s thrust comes from a jet of air or exhaust being sent rearward.
Example Sentence 1
Most airliners today are jet-propelled aircraft, using turbofan engines to produce thrust by accelerating air rearward.
Example Sentence 2
Many airline routes are flown in jet-propelled aircraft because they maintain high speeds at altitude.