Definition
A reciprocating aircraft engine designed to maintain its rated sea-level horsepower up to a specified higher altitude, above which power output begins to decrease as altitude increases.
Plain English
An engine built to keep producing its full sea-level power as the airplane climbs, up to a certain altitude. Above that altitude, it loses power like a normal engine.
Context Anchor
Seen in aircraft engine descriptions, performance planning, and discussions of how engine power changes with altitude.
Derivation
Altitude comes from the Latin word altus, meaning high. In this term, altitude points to the key idea: the engine can maintain its approved takeoff power up to a certain height above sea level.
Why Pilots Care
It allows the aircraft to climb higher and fly faster without the power loss that occurs in normally aspirated engines as air density drops.
Intuition Check
Do not read altitude engine as simply any engine that can run at altitude. Here it means an engine approved to make full takeoff power up to a specified altitude.
Example Sentence 1
Because the aircraft has an altitude engine, the pilot could expect full rated horsepower on takeoff from the high-elevation airport.
Example Sentence 2
During the preflight briefing the instructor explained that the altitude engine would continue producing sea-level horsepower well above the airport elevation.