Definition
The highest power output, expressed in horsepower, that an engine is certificated to produce continuously or for a specified time period under defined operating conditions, as established by the manufacturer and approved during certification.
Plain English
The most power the engine is officially allowed to make, as set by the people who built and certified it.
Context Anchor
Seen in constant-speed propeller operation and airplane operating information when discussing takeoff, climb, and approved power settings.
Derivation
"Rated" comes from the Latin rata, meaning a fixed or assigned amount. A "rating" here is the manufacturer's assigned, certified limit — not a casual estimate.
Why Pilots Care
Operating above this limit risks engine damage; using it correctly delivers the performance the aircraft was certificated to achieve.
Intuition Check
Maximum rated horsepower does not mean the engine should be run at that power all the time. It means that is the approved top power, and the airplane’s operating information tells when and how long it may be used.
Example Sentence 1
At full throttle and the recommended RPM for takeoff, the engine is producing its maximum rated horsepower.
Example Sentence 2
The engine logbook showed the maximum rated horsepower was 260 at 2,700 RPM.