by Rick Braunig
Manager of Aviation Safety & Enforcement
MnDOT Office of Aeronautics
Published in Midwest Flyer – April/May 2020 issue
I hire pilots for our office and one of my favorite questions is: How do you know you have enough runway when taking off on a turf runway? About the best answer I get is to check the performance charts in the aircraft operator’s manual and then add some safety factor like 20%. Of course, this doesn’t take into account the length of the grass, nor whether the grass is wet or even how close the aircraft’s performance matches to the numbers you get from the charts in the book. The answer I’m looking for is “three quarters by one half.” If you have three quarters of your takeoff speed by the time you reach halfway down the runway, you can feel confident that you will be able to takeoff in the remaining portion of the runway. If not, you have the second half of the runway to get stopped.
I do think it is a good idea to run through the performance charts. The question then is, how closely does my performance match the book numbers? I wouldn’t expect the performance on my 1984 Bonanza to be better than what the company pilots got when the aircraft was factory fresh, but how much luster have I lost? Has1,800 feet become 2,000 feet? After all, the time to figure out if you can take off on that short runway is before you land there. It is really embarrassing to have to pull the wings off and get your aircraft trucked to a different airport, costly too. So, if you want to check your numbers, one way to do it is to count runway lights. Runway lights are normally spaced 200 feet apart. You should run the numbers and then test it on takeoff to get a feel for the difference between what the book says and your actual performance.
Knowing how your aircraft normally acts on takeoff can also help you to catch when something isn’t quite right. I took off one day and noticed my airspeeds were lower than normal. I made a precautionary landing short of my destination and when they opened up the engine only five of the six cylinders were running. The sound was normal and there was no vibration, but the performance was off. Knowing what is normal allowed me to get the aircraft on the ground before I was at a point where the engine was failing. Even better would have been to stay on the ground and not have gotten airborne at all.
Conditions change, temperatures rise and fall, pressure altitude changes, so only by running the numbers regularly and checking how closely your aircraft matches to the numbers, do we get an appreciation for what to expect. Even if you don’t operate off short runways, you want to catch a change in your performance that may indicate a problem before it becomes an emergency.
What role does a crosswind play on your takeoff role? On approach a crosswind requires wing down and opposite rudder which increases drag. On takeoff you need to estimate the aileron correction for the crosswind and in a strong or gusty crosswind you may want to delay your liftoff to ensure you can keep flying and to prevent being blown off centerline, resulting in the tap dance towards the runway lights. That extends your ground roll. How much? Increase your lift off speed and use the three quarters by one half guideline.
I always say helicopters are more sophisticated than airplanes. In the helicopter, you pull up on the collective and if you reach the top and the machine isn’t flying, you lower the collective and kick someone or something out. In an airplane, you go as fast as you can towards those trees at the end of the runway and hope that the machine will fly before you get there. Use this tool. It has a better success rate than hope. Now I have to find another question for my interviews.
