There is no doubt that the PT6 captured the market. Today, there are no Garrett powered IR SETP's around, and few twins. That doesn't mean there's something wrong with the Garretts. That's just how things evolved. Coke vs Pepsi.
At the time of their introduction the PT6's were a good deal economically. They are no longer.
P&W has, as their market share has increased, also jacked up their prices. An overhaul of a PT6 is today an eye watering affair and costs much more than a Garrett, although the Garrett has 1800hrs longer TBO. You can overhaul two engines on the Twin Commander, for the same price as one on the PC12. And get an extra 1800hr TBO. Not only that, the Commander will burn less fuel than the single in the PC12.
As for STC extension programs, they exist for Garretts as well. 7000hr is just an SB and a program, and up to 9000hr are done on the crop duster Trush planes I've heard.
Last edited by AdamFrisch; 18th Oct 2015 at 15:00.