After reading * that there have been 96 accidents in various models of the Rockwell Commander 690 since May 1969, I have gained a new respect for the level of piloting skill that is required to fly one. I spent time reviewing some articles concerned with the piloting of twin turboprops and turboprops in general. I now appreciate that they are really considerably more complex than their smaller conventionally powered cousins e.g. the Beech Barons, Cessna 300 and 400 series etc.
All one has to do is to look at the pictures of the cockpits, with special attention to the engine and prop controls, as well as to the engine instrument gauges to gain a new perspective. The fixed shaft Garrett engines that power the 690 have four engine gauges per engine. While the Pratt & Whitney PT-6 which powers the King Air has six gauges per engine. That’s a lot to pay attention to. The main time the pilot must watch these gauges is at start-up so as not to exceed a critical engine temperature. Failure to do this might result in a Hot Start, with resultant engine damage if the engine is not immediately shut down. Anyway, this is just to make us aware that the turboprop engine requires more out of the pilot as compared to the conventional piston powered type engine.
The planes themselves are heavier than their piston counterparts such as the C-310, Pa-31 or B-58 by several thousand pounds. Critical stall speeds are higher. For example the stall speed with full flaps and gear (dirty) is 75 kn, while in a Pa-31 Navajo, a plane I used to fly (and love), stall speed dirty is 65 Kn. Big difference, especially for the non-professional. OK, now maybe you see where I am heading with this. In order to feel competent when flying any of the planes I used fly, whether Pa-31 or a Bonanza, I needed to fly a lot, frequently as often as once a week or more. To think that I could comfortably handle the complexities of a twin turboprop, as a non-professional on a casual basis is just out of the question.
So, in my opinion, the pilots of the recently crashed Aero Commanders had a lot to contend with. Maybe when everything is just fine, both engines purring along, weather not too bad, field in sight and cleared to land, all is OK. But as in New Haven, things can get a bit dicey, quickly. Weather getting bad, a sudden runway change and too much to deal with in a demanding plane can be overwhelming. The other crash occurred during recurrent training at 12 to 15 thousand feet. It isn’t that hard to enter a single engine stall when the nose of a heavy plane is pulled up a bit too far with one engine idled. But it is almost impossible to escape a flat spin when one is accidentally entered. These usually end with a fatal crash. That is one scenario I suspect happened as discussed in my article of July 5, 2013 in Operationsafeflight.blogspot.com.
In summary. The twin turboprop is considerably more difficult to fly than the smaller conventionally powered twins. That means piloting a turboprop requires considerably more skill and training than some may believe. The statistics are a bit scary as are the recent number of crashes. Future turbo pilots beware and prepare.