Don't provoke the "money gauge"
Pilots thinking about moving up from piston- to turbine-powered airplanes dream of how much more power they'll be able to command. While it's true that many turbine engines have higher power ratings than large piston engines, there's no free ride.
Turboprop and turbofan engines are designed by top-notch engineers and built using the best of materials, but like all engines they still have a weak spot: They're very sensitive to temperature extremes. If you're not careful, it can be very easy to make a turbine engine's hot section (combustion chamber) overheat.
A hot section overtemp is serious — serious enough for manufacturers to require very expensive (we're talking deep into five figures) engine teardowns and hot section inspections, and even more expensive component replacements if an engine's temperature redlines have been exceeded by specified time periods. These times are expressed in mere seconds. You can find these redlines on interturbine temperature (ITT) or exhaust gas temperature (EGT) gauges. If your job is flying turbines and you let these needles drift past redline — well, you might want to consider another line of work. That's why the ITT and EGT gauges are called the résumé gauges or money gauges. That's also why many manufacturers put these gauges at the top of the engine instrument stack(s).
Overtemps usually happen during starts, during takeoff, or when climbing at high power settings. When starting a turbine, it's very important to draw plenty of air through the engine before adding fuel and attempting a lightoff. You do this by spooling the engine up to a certain value — say, 12 percent compressor speed — and then lighting the fire by moving the condition lever to the On, Ground Start, or Low Idle position, depending on how your airplane's fuel controls and ignition systems are set up. Of course, follow the specific advice contained in the airplane's pilot's operating handbook.
Introduce fuel before enough air is moving through the combustion chamber, and it can burn out of control. The résumé gauge will soar. The only corrective action is to shut off the fuel and motor the engine (turn the engine with the fuel and ignitors off) in an attempt to purge it of fuel and heat. But all that's after the fact. Serious engine damage may have already occurred. A teardown and inspection will be the only way to verify just how bad the damage was.
On takeoff, overtemps can happen when high density altitudes prevail. There will be less engine cooling if ambient temperatures are hot, and if you advance the power too far or too fast, then ITTs or EGTs can head for redline. The job here is to keep a close eye on the money gauge(s) as takeoff power is being set. Stop advancing power when the ITT or EGT needles come close to redline. At this point, that's all the thrust you'll be able to use for takeoff. Your available power is now temperature-limited, meaning that you won't be able to increase the engine's torque or fan speed without busting the ITT or EGT redline. Naturally, you've already calculated your takeoff performance and know that you'll have enough runway for a safe takeoff acceleration and climbout.
As air density decreases in the climb, high ITTs and EGTs can once again limit the amount of thrust that you can use. Thinner air means less cooling, and above-standard outside air temperatures can also cause ITTs and EGTs to run hot at climb power. Even at standard or below-standard temperature conditions, most turboprop engines' money gauges begin to close in on redline at about 18,000 to 25,000 feet, depending on the outside air temperature. At or above those altitudes, the power levers have to be pulled back slightly to prevent an excursion into redline territory. That's one reason why turboprops realize their maximum speeds at that altitude range. Turbofan engines experience the same temperature-limiting phenomenon, but at higher altitudes.
So yes, turbine pilots have more power at their disposal. But managing that power calls for a temperature awareness much greater than that needed for flying with a piston engine. Turbine overtemps can happen breathtakingly fast.
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