“Can I perform a reduced power takeoff to save wear and tear on my engines?”
We get this question fairly frequently at King Air Academy and the short answer is no, you can’t do a reduced power takeoff. Naturally, the follow-up question is “Why?”
We don’t have charts that give us the performance numbers we need to make a safe decision. Beechcraft has never published reduced power takeoff data for King Airs. Without that data we don’t know how our plane is going to perform given the conditions in which we are flying. If you choose to perform a reduced power takeoff, you are becoming a test pilot.
Speaking of knowing if our performance data is accurate, how do we know that our aircraft can meet the requirements of the flight? Before we fly, we check takeoff distances, accelerate/stop distances, climb gradients and single-engine performance, among others. All those charts have been created by the manufacturer so that we know what to expect and plan for during our flight. However, what makes those charts true after they have been created? Our performance data is based on minimum acceptable power being produced by our engines. How do we know what that is? We have a chart for that!
The minimum takeoff power chart
This chart tells us the minimum amount of torque we need to produce from our engines to make our performance charts true.
Figures 1 and 2 (next page) are for a King Air B200 (BB-1439; BB-1444 thru BB-1842, except BB-1463 & BB-1834; BL-139 thru BL-147; BW-1 thru BW-29). Make sure you are using the appropriate charts for your model and any modifications made to it when making your calculations.
Please read the notes carefully; they contain important information.
Note No. 1 on both charts says that torque will increase approximately 20 ft-lbs from zero to 65 knots. Why is this important? As we increase speed, air going into the engine compresses slightly giving us ram rise – a small increase in torque. The chart is valid, in this example, at 65 knots.
But what is this telling us? It says that at our field temperature and pressure altitude we should produce X amount of torque before becoming ITT limited. If we produce or exceed the amount of torque required by the chart (at 65 knots), then our performance calculations will be true. If we don’t, then our performance numbers will not be accurate and cannot be relied upon.
Notice that Figure 2, showing ice vanes extended, has a large grey area. The 200 series cannot have its ice vanes extended above 15 degrees Celsius. Take a look at the different minimum acceptable torque numbers between the two charts. On the ice vanes retracted chart (Figure 1), you would expect to make maximum torque before becoming ITT limited for a 10 degrees Celsius day at a pressure altitude of 4,000 feet. Using the same temperature and pressure altitude on the ice vanes extended chart (Figure 2) results in a minimum acceptable torque of 2,160 ft-lbs before becoming ITT limited. If you cannot make the minimum torque at 65 knots then you do not know if your airplane is capable of performing the way you expect it to.
Finally, one of the things that many pilots do is use a slightly lower than maximum power setting in cruise to help preserve their engines. This a normal and accepted practice. What is not done nearly as often is checking to make sure you are producing book torque and speed in cruise. Why do we need to check this? It tells us if our engines are working the way they are supposed to.
The maximum cruise power chart
Figure 3 (above left) shows the maximum cruise power chart for a King Air B200; please use the appropriate chart for your aircraft.
This chart shows that at FL240 on an ISA day, you should be able to set 1,920 ft-lbs torque without exceeding ITT limitations. This should result in an indicated air speed of 196 and a true air speed of 284 knots at 12,000 lbs. If you cannot achieve book speeds and torques it might be worth looking into. Be aware that some common modifications to King Airs will alter an aircraft’s speed, such as wing lockers, high float gear, extra antennas, etc.
Remember, don’t be a test pilot. Make sure your engines are producing enough power to make your performance charts true. The max speed check is an indicator of your engine’s health, so check it once in a while.
Zach Cleaver, a Gold Seal flight instructor since 2009, started teaching in King Airs in 2010. He has worked for King Air Academy in Phoenix, Arizona, since 2013 and flies all models of King Airs.