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tend to outperform turbocharged piston airplanes at most altitudes. It’s important for you to know, however, that turboprop airplane performance decreases with increases in density altitude.
Piston engines are controlled by throttles, propeller RPM and fuel mixture controls. Turboprops come in two basic designs: fixed shaft and free turbine. Fixed shaft turboprops, in which the propeller is directly connected to the engine and rotates any time the engine is running, use a power lever (sometimes called thrust lever) and a condition lever. The power lever adjusts torque and propeller speed. The condition lever controls engine speed and fuel flow. Free turbine (or split shaft) turboprops have a propeller coupling that permits the turbine to run without spinning the propel- ler. Free turbine engines have three engine controls: the power lever, setting pressure or torque output; a propeller RPM control, adjusting propeller speed (generally much slower than piston propeller speeds, usually 1500 to 1900 RPM); and a condition lever that is basically on ON/OFF control for the fuel. Leaning is not required in any turbo- prop engine but is controlled automatically when the pilot sets the power lever.
Turboprops have strict operating limits of torque, internal temperature, and rotational speed. Unlike piston airplanes, in which “full throttle” is almost universally correct for takeoff, it is almost never appropriate to push the power lever to the forward stop in turboprops. Exceeding torque engine speed or temperature limits for even a few seconds can be catastrophic to the engine. During engine start, you must watch for a “hot start” condition, that is, exceeding temperature limits, and immediately shut down the engine if it overtemps (the term is the same, but this is completely unrelated to “hot starts” in fuel-injected, piston engines). During the takeoff roll and climb, you must carefully watch the torque gauges, engine speed and temperature gauges, and advance the power lever only until reaching the maxi- mum permissible amount on any one indicator. It’s usually possible (and a very good idea) to predict ahead of time which variable – torque engine speed or temperature – will be the limiting factor for a given takeoff. Include this
determination in your preflight planning. As the airplane climbs and power output decreases, you may be able to ad- vance the power lever to maintain or even increase power in climb, as long as the engine stays within all of its limits.
Almost all turboprops have a reversible-pitch propeller. This permits you to direct thrust forward to dramatically shorten landing distances. You’ll reverse the propeller by pulling the power lever all the way aft and over a stop. There are limits on reverse thrust, so you’ll have to use this capability carefully. Like piston twin airplanes, SETP propellers are featherable. This reduces drag in the event of an engine failure, in the case of SETPs to increase glide distance. Despite their famed engine reliability, you still need to be ready for engine failures in turboprops.
You might think that, understanding the operation of a turboprop powerplant, that you’ll know what you need to safely fly a SETP. However, the reality is that knowing how the engine works is a small part of flying a turboprop. Here are some of the other considerations:
Systems
Most piston aircraft systems are incredibly simple in comparison to SETPs. As one measure of the quantum leap in complexity, count the circuit breakers in even a pressurized piston twin and compare that to the number in a SETP. Ice protection, electrical inverters, and in almost all cases, pressurization – you’ll need to spend time “in the book” learning how each system operates in normal, abnormal and emergency situations. You are still a pilot in a turboprop, but you are just as much a systems manager.
To manage the systems properly you’ll need to be strict about checklist use...not because you can’t learn to f ly a SETP without them, but because they are so complex it is more likely you’ll miss something in high workload environments.
Flight Environment
Most, but not all, SETPs are pressurized. All turboprops are more efficient above 10,000 feet. When transitioning you’ll need to become comfortable and capable in a me- dium- to high-altitude environment. Studies on hypoxia, supplemental oxygen use, high altitude navigation and
meteorology are just as important in your studies as the airplane’s flight manual. If the airplane is pressurized and its maxi- mum certificated altitude is above 25,000 feet, you’ll need a High Altitude endorse- ment to fly as pilot-in-command. Training for this endorsement should cover all the specialized high-altitude topics I listed. In the Flight Levels you’re operating in the same airspace as airline and military
Even simple SETP systems are likely far more complex than in piston aircraft. Plan to spend a lot of ground time working toward mastery of how everything works, so you know how to use it in normal, abnormal and emergency situations.
January 2021 / TWIN & TURBINE • 7