Gas turbines can produce more thrust with lower outside air temperatures.
It also allows for keeping structural forces and asymmetric thrust, in case of an engine failure, within limits.
Engines are typically flat rated for a range of equivalent sea level temperatures, such as ISA+15°C and below.
For example, the Garrett AiResearch TPE-331-5 engine originally fitted on the Dornier 228 produces 715 horsepower (533 kW).
The Dornier 228 can also be fitted with the Garrett AiResearch TPE-331-10 conversion of the -5 engine which produces 1,000 horsepower (750 kW) but is limited (flat rated) to only 715.