Definition
Airplanes powered by a single piston engine, in which fuel is burned inside cylinders to drive pistons that turn a crankshaft connected to the propeller. These are the most common type of training and personal aircraft, typically operating at lower speeds and altitudes than turbine-powered airplanes.
Plain English
Small airplanes with one engine that works like a car engine, using pistons moving up and down inside cylinders to spin the propeller.
Context Anchor
You may see this phrase in discussions of non-towered airport traffic, where many arriving and departing aircraft are small training or personal airplanes.
Derivation
Piston comes from the Italian pistone, meaning a large pestle that pounds up and down. The engine works the same way -- pistons pumping inside cylinders. Single-engine simply means one engine, distinguishing it from twin-engine or multi-engine airplanes.
Why Pilots Care
Piston single-engine airplanes have specific performance limits -- slower approach speeds, shorter ranges, and different traffic pattern speeds than turbine aircraft. At non-towered airports, knowing what type of airplane is in the pattern with you helps predict closure rates and spacing.
Intuition Check
Do not read this as meaning every small airplane. It specifically means an airplane with one piston engine; some small airplanes may have two engines or turbine engines.
Example Sentence 1
Most traffic at the non-towered airport consisted of piston single-engine airplanes flying standard left-hand patterns at 1,000 feet AGL.
Example Sentence 2
Piston single-engine airplanes normally enter the downwind leg at 1000 feet above the airport elevation.