Definition
A type of turbine engine starter that uses a high-velocity stream of compressed air directed onto the turbine or compressor blades to spin the engine up to starting speed. The air is supplied from an external source such as a ground cart, an auxiliary power unit, or a cross-bleed from another running engine.
Plain English
A starter that gets a jet engine spinning by blasting compressed air directly onto its internal blades, like blowing hard on a pinwheel to make it turn.
Context Anchor
Seen in turbine-engine starting system descriptions and maintenance procedures, especially where compressed air is used instead of an electric starter motor.
Derivation
Impingement comes from the Latin impingere, meaning to strike against or push into. The name describes exactly what happens: the air strikes against the blades to drive them around.
Why Pilots Care
Provides a lightweight starting method for certain turbine engines without relying on large electric motors.
Analogy
It is like blowing on a pinwheel: the air hits the blades and makes them turn. In the engine, the air is much stronger and is aimed through nozzles.
Intuition Check
Do not picture an electric motor turning the engine through a shaft. In an air impingement starter, the air itself strikes the blades and starts the rotation.
Example Sentence 1
Before engine start, the ground crew connected the air cart to supply the air impingement starter.
Example Sentence 2
On this aircraft the air impingement starter spins the turbine up to ignition speed using bleed air from the APU.