Because of the number of queries we receive over the years, there are a great many questions about how the power output of turboprop engines is determined. With ever more powerful engines being installed at the factory in the TBM and PC-12 singles, and conversions offered on existing twins by Blackhawk and others, it’s understandable that pilots are confused.
To understand what’s going on with the performance improvements from the more powerful Pratt & Whitney PT6 engines involved, you need to know that there are two fundamental measures of power. The most basic measure of power—and the one listed in the airplane specifications—is the maximum shaft horsepower (shp) of the engine. The other element in the power equation is how much power the engine can potentially produce at sea level on a standard 15 degree Celsius day, which are the international standard atmosphere (ISA) conditions.
