Definition
A reciprocating aircraft engine fitted with a supercharger or turbocharger that is sized to deliver rated sea-level manifold pressure only at sea level. As the aircraft climbs, the boosting device cannot maintain that pressure, so power output falls off with altitude in the same general way as a normally aspirated engine, just from a higher starting point.
Plain English
An engine with a built-in air pump that gives it full power at sea level but cannot keep that full power as the aircraft climbs higher.
Context Anchor
Seen in engine performance, turbocharger, supercharger, and aircraft powerplant discussions.
Derivation
"Boosted" comes from the idea of giving the engine an extra push of air. "Sea-level" tells you the altitude at which that boost reaches its rated value — so the name is shorthand for "boosted, but only up to sea-level rating."
Why Pilots Care
Delivers consistent takeoff and climb power at higher elevations where normally aspirated engines lose performance.
Grounding Statement
As the airplane climbs and the outside air gets thinner, the boosting system helps pack enough air into the engine to keep power from dropping right away.
Intuition Check
Do not read “sea-level boosted” as “only boosted at sea level.” It means boosted so the engine can keep sea-level-rated power while climbing, within its design limits.
Example Sentence 1
Because the trainer had a sea-level boosted engine, the instructor reminded the student that climb performance would steadily decrease as they gained altitude.
Example Sentence 2
After the climb, the pilot noted the sea-level boosted engine still delivered rated manifold pressure at 6,000 feet.