Page 29 - Volume 13 Number 10

Ask the Expert
Using Big Numbers
by Tom Clements
Years ago, I was conducting recurrent King Air Beech’s choice of V1/VR for the 200, I have no problem
200 training with the two experienced and
professional pilots of a Midwest corporation. As part of their takeoff briefing, they used the phrase, “We’ll use big numbers.”
“What did you say?” I asked. “What does that mean?”
Their explanation made a lot of sense to me then, as it does now. It is a procedure that I have adopted and use regularly. I believe it adds a degree of safety that helps to stack the deck in our favor. With one very minor exception – that I will address later in this article – I can see no detriment or downside to it whatsoever. Let me explain.
Not all King Air models have differing takeoff speed numbers depending on conditions. The fine E90 model, for example, bases all of its takeoff data on using a rotate speed of 95 KIAS (knots indicated airspeed) and a 50-foot speed of 100 KIAS. Although Beech does not use the terms V1 and V2 for the E90 – reflecting its date of certification, its weight, and the rules that then applied – those two numbers would be the 95 and 100. These speeds apply to all airport elevations, all outside air temperatures and all weights. I much appreciate the simplicity they provide. Although they may not be “perfect” for all situations, the E90 is such a fine performer that it does very well using them in all situations.
As the King Air history evolved and the larger and heavier model 200 appeared – with first deliveries in 1974 – takeoff numbers became more elaborate. Although I have written and spoken about my disagreement with
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whatsoever with their V2 choices. V2 varies from a low of 99 KIAS – while using approach flaps for takeoff at a light weight of 9,000 pounds – to a high of 121 KIAS – clean, at the maximum gross weight figure of 12,500 pounds. Similarly, the 300-series use a wide range of V-speeds that vary based on flap setting and weight.
Here’s the idea of “big numbers”: The day that I first learned of this technique – with the two pilots of the 200 in the Midwest – we were about to depart from an elevation of 800 feet, at 11,500 pounds, with an OAT of 20°C, and about an 8-knot headwind component. However, the crew – years before in the comfort of their hangar office – had worked out a lot of takeoff performance problems for their own home-base airport as well as other airports they frequently used. In all cases, they did the exercise based on worse-than- expected conditions. In this home-base case, they used 1,000 feet elevation, 45°C temperature, 12,500 pounds, no wind, no flaps. They found that both Accelerate-Stop and Accelerate-Go distances were less than the 8,000- foot runway they would be using.
If the airplane can perform satisfactorily using these worse-than-actual conditions, then is it not correct to believe that the actual performance will be better than (and certainly no worse than!) the performance numbers the POH provides even if we use the higher V-speeds for the higher weight? After all, we will reach those speeds in less time and our climb rate, using the higher V2, will be greater than the chart presents since we are at a lighter weight. As a side benefit, our margin
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