Author’s Note: This is a repeat of my article written for the December 2014 issue of this magazine. It also comprises the chapter starting on Page 307 of The King Air Book – Volume II. Obviously, I think it is important enough to review once more.
Rarely do we pilots need to apply rapid and full power from idle. While initiating a takeoff roll or leveling off after an idle power descent, we have plenty of time to advance the power levers slowly. Most go-arounds or balked landings are begun before the power levers were moved all the way back to idle.
The two situations in which we do need to have a proper, rapid idle-to-maximum-power technique are idle power stall practice for training – or for real, if we ever let ourselves get into that unfortunate situation – and a balked landing from deep into the flare, nearly at touchdown.
I wager there are many King Air pilots who have never encountered either of these two situations before and who may well complete their entire King Air flying careers without ever encountering them. That’s great! Furthermore, if they ever do encounter these rare situations, they will probably muddle through just fine by advancing the power levers at whatever rate they choose to use. Based upon my observation of hundreds of pilots during King Air flight training, however, there is a simple and effective technique that I want to pass along.
It is rare that two different PT6s accelerate from idle at the same rate. Realize that the power levers do not affect fuel flow and power directly. Instead, they merely set a speedier spring tension that causes the fuel control unit (FCU) to reach and maintain a particular N1 or Ng speed, compressor speed. It’s the FCU that adjusts fuel flow and power in response to the pilot’s request for new N1 speed.
Since the FCU has “a mind of its own” about how to accelerate when suddenly told to go to a much higher N1 speed following a “throttle slam,” it is not uncommon to find that one engine will reach takeoff power before the other engine has even reached 30% power. Handling such a large power difference at low airspeed when the rudder is not very effective can be a challenge. Furthermore, it is impossible to know exactly what torque and ITT will finally be reached when the engine stabilizes and there is a strong probability that limits may be exceeded.
That’s why a couple of undesirable outcomes await the pilot who moves the power levers too far, too quickly, when faced with a “need-it-now!” high power requirement.
A better technique is to do what I call a “Bump and Run” with the power levers. When the stall horn starts to sound unexpectedly or when the deer suddenly appears in the landing lights in the flare, immediately bump the power levers forward as fast as possible but only about one-third of the way. “One one-thousand, two one-thousand, three one-thousand.” Pause for three seconds, then run the power levers forward rapidly as you watch the torque and temperature gauges, stopping when you are at or near takeoff power.
Why does this work so well?
Each position of the power lever corresponds to a unique N1. Since low idle is usually near 60% N1 and “full throttle” is slightly over 100% N1, our one-third forward “bump” means that we have requested about 73%, slightly more than high idle. To clarify, since the difference between 60 and 100 is 40, one-third of that is a little over 13. 60 + 13 = 73. No matter how mis-matched in acceleration rates your two engines happen to be, the power being produced will remain low enough that no significant asymmetrical thrust can be achieved. (Realize that 73% N1 is much, much less than 73% power.) But by the time three seconds have elapsed, both engines will be stable at this elevated N1 speed, meaning that the response rate of the engine to power lever movement will now be virtually instantaneous, with no spool-up lag. Torque and ITT will increase right in sync with power lever motion and the desired values can be reached without overshoots.
Back in the 1970s I was using the GI Bill to pay for my Learjet type rating through FlightSafety International in Wichita, Kansas. The airplane I actually flew was a model 25C equipped with the CJ610 straight jet engines. It was there that I was first taught about “throttle slams.” Recovering from an imminent stall at idle power, we were taught to slam the thrust levers forward to the stops, then pull them back one-half inch. Like magic, this worked exceedingly well, yielding a high but not excessive power in a short time period. Although it was common that one engine accelerated much faster than the other, the resultant asymmetry never seemed excessive due to the fuselage-mounted engine location.
Trying this same technique on King Airs – going forward to the stops and back a half-inch – always kept torque and ITT within limits but when the two engines had very different acceleration rates the yaw tendency was rather fierce, since the engines were mounted outboard on the wings. That’s why the one-third forward bump, the slight delay, and then the rapid run to the desired power works much more successfully.
As stated at the start, you may well never need to use this technique. But practice it a time or two when you next fly your King Air – not necessarily in a stall recovery or balked landing situation, but just “playing” with the power levers, starting with them at idle – and see what results. You can even do it with the brakes locked when beginning a takeoff roll on a longer runway. I suggest you release the brakes and start rolling after the post-bump, three-second delay.
I think you will want to add this Bump and Run arrow to your quiver of operating techniques.