Ask the Expert: Applying Takeoff Power … and Never Being Surprised Again

Ask the Expert: Applying Takeoff Power … and Never Being Surprised Again

Ask the Expert: Applying Takeoff Power … and Never Being Surprised Again

I addressed this in an article many moons ago, but I still observe lots of King Air pilots who have never been taught the trick that makes setting takeoff power easier and better than the technique they are currently using. The trick? Do not look at the Torque or ITT gauges until you have monitored the propeller speed gauges and verified that they stabilize at the proper takeoff RPM.

For the great majority of you who have the engine instruments arranged in a vertical stack, always make your scan from bottom to top, not top to bottom, when the checklist issues an “Engine Instruments” challenge. We cannot really operate the airplane normally and successfully without looking at the top three instruments often: ITT, Torque, and Propeller Speed (Np). Yet the bottom three – Gas Generator Speed (N1), Fuel Flow (Wf), and Oil Temperature/Oil Pressure – get the short end of our attention stick. Seek them out first before going up to the ones that are your old friends. Doing so increases the chances that you will spot any abnormality in these “out of sight, out of mind” gauges.

Following in this habit pattern, as you start adding takeoff power, scan the gauges from bottom to top. A quick check of the Oil Temp and Oil Pressure verifies that a missing or loose oil dipstick has not yet wreaked any havoc. Fuel Flow and N1? Not much to see there now. But now the important Np display draws our needed attention.

Perhaps a lot of King Air pilots have unrealistic expectations when it comes to engine control rigging. Yes, in an ideal world, we could advance the power levers side-by-side and both engines would accelerate in perfect synchronization. But in the real world, it very, very rarely works that way! This is why it works so well to watch those Np gauges like a hawk as you s-l-o-w-l-y begin to advance the power. When one side’s propeller speed starts getting ahead of the other side, then stop advancing that side’s lever, slide the other side’s lever forward a bit, and get those prop speeds matched again.

Why did I emphasize doing this s-l-o-w-l-y? To avoid unnecessarily large ITT spikes. When the engine is at Low Idle – and this is especially true for the three-blade King Airs with their Idle N1 set closer to 50 percent instead of 60 percent – there is not a lot of excess air for cooling. If the power levers are advanced rapidly, the ITT will rise dramatically as fuel is introduced by the FCU (Fuel Control Unit), but then fall as the engine accelerates and brings in more cooling air. This rise and fall is the ITT “spike.”

Once N1 speed reaches the High Idle setting of about 70 percent, the engine is able to accelerate more rapidly with hardly any ITT spike at all since the air and the fuel flow increases are better matched.

In every PT6-powered King Air, by the time Np reaches 1,500 RPM on the ground, N1 will be great enough that the ITT spiking is not a factor. Also, the mis-match of engine acceleration rates is much less troublesome. Hence, after the prop speed gets to 1,500, move the power levers as rapidly as you wish while still splitting the levers as required to keep the prop speed closely matched, left and right.

As Np gets within 10 or 20 RPM of takeoff redline, slow or even stop power lever movement momentarily to allow the Primary Propeller Governor to begin its function smoothly and without surging. Not only is this smoother overall, but it 100 percent guarantees that you will observe that the primary governor is truly working correctly. Until pilots have learned to watch the props before torques and temps, it is depressing how many continue a takeoff in the simulator even though one side’s prop speed is stabilized on the Overspeed Governor’s setting. This error will never happen when the propeller gauges are monitored first during the takeoff power application.

Once it is confirmed that propeller speed has become properly governed, now is the time to move the power levers rapidly while monitoring torque and ITT. I guess that by now you are quite familiar with the operation of your particular powerplants and will have a good feel for whether full torque can or cannot be reached because of ITT constraints. In the C90GT-series, in the Blackhawk-modified C90 and E90 models, as well as in -52, or -61-powered members of the 200-series, ITT is never a limiting factor if the engine is performing correctly. It cannot get high or hot enough for takeoff power ever to be limited! (Well, maybe in the summer departing from La Paz, Bolivia, with an elevation of 13,325 feet.) On the other hand, the old A90, B90, and C90s powered by the -20 or -20A versions of the PT6 rarely can reach maximum torque, even at Sea Level, when the OAT is hot. Similarly, it does not take much elevation and temperature increases before the 300-series will run into ITT constraints.

“Golly, Tom! It sounds like it’s going to take an eternity to set takeoff power!” Yes, it probably does sound like that, but truly it does not. Of course, if we are going “by the book,” we set takeoff power before brake release anyway so how long it takes is immaterial. But doing the more common rolling takeoff – on a comfortably long runway – the technique I am teaching can be used and yet full power can be easily attained by the time the airspeed reads 40 knots. It may be hard to believe, but it’s true. (Watch some of the videos on the YouTube King Air Academy channel and you will see for yourself.) We only go quite slowly until the props are together at 1,500 RPM, then faster and with a small pause as the props hit governing speed, and then very rapidly to target torque or ITT.

As I stated, advancing the power levers side-by-side almost never gives equal power. But there are times when we may intentionally want different left and right power. Due to the natural left-turning tendency caused by the clockwise-rotating props, some pilots prefer to have slightly higher power on the left than the right side to combat that tendency without using as much rudder. In a string crosswind, also, leading with the upwind engine is quite common and effective. However, my suggestion is to create the torque split with the power levers only after you have used them to smoothly get the propeller speeds matched at the takeoff setting.

Any pilot who spends lots of time with one particular airplane will learn, on a trial-and-error basis, how to best advance power for takeoff and achieve the straight and smooth roll that he or she desires. The technique that I am advocating here will permit you to get in the cockpit of any PT6-powered twin and make your first takeoff power application as nice as your hundredth!

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