Texas Turbines spent an extensive amount of time researching the best engine to mate to the Cessna Caravan. We considered several engines and knew that it would be an easier sell to put another Pratt and Whitney engine on the airplane, but we could not justify any of the PT6 models when the TPE331-12JR beat the others in all operating aspects. The following engines were considered:
Pratt & Whitney: PT6A-135A, PT6A-34, and the PT6A-42A
Honeywell: TPE331-10 and TPE331-12JR
The PT6A-34 and PT6A-135A were ruled out early for a multitude of reasons. The -34 was eliminated because of the higher prop rpm and noise level for takeoff, dual exhaust issue, and the lower thermodynamic rating as compared to the -114A, although it did have a higher gearbox limit (750 shp). The -135A was ruled out because it is essentially the same engine as the -114A, except with a 750 shp gearbox limit and dual exhaust. Thermodynamically the -135A has the same power as the -114A at altitude unless you want to run it hotter, which will cost more to overhaul if it makes it there. There have already been enough CT blade issues with the PT6 engine. Running the engine hotter will only cause more issues.
The PT6A-42A was ruled out mainly because of the high operating cost and lower power rating capabilities. The Honeywell TPE331-10 and -12 engines can typically be operated less than the PT6A-114A on the same TBO. Refer to the head to head comparison below.
Head to Head Caravan Comparison
TPE331-12JR vs PT6A-42A
The Honeywell TPE331 engine was chosen for superior fuel specifics, faster power response, higher base TBO, and lower operating cost per horsepower. The engine has proven its reliability in commercial operations around the world and has an in-flight shutdown rate as good, or better, than any engine on the market today. It just makes economic and pilot sense to choose the TPE331-12JR to power the Caravan.