![A mechanical E6-B can help you do ground speed check in flight. [Courtesy: Meg Godlewski]](https://flyingmag1.b-cdn.net/wp-content/uploads/sites/2/2025/09/IMG_4955-scaled.jpeg?width=1920&height=2560)
Question: How can I do a ground speed check without going off course and altitude? I do the math on the ground to determine my ground speed using the mechanical E6-B. But when I do a ground speed check at altitude during the flight, it takes me so long that the aircraft drifts off heading and altitude. I am a student pilot flying a Cessna 172P that doesn’t have an autopilot. I tried using one of those calculator E6-Bs, and it didn’t help.
Answer: Are you trimming the aircraft for level flight once you are in cruise? That’s step one. Step two is making sure you don’t make more work for yourself by erasing the wind dot on the mechanical E6-B after you have completed your calculations on the ground.
Before the flight, put the wind dot on the wind side of the unit in a big, bold fashion, and leave it there until the flight is over and done. If you have multiple legs of the flight that require different ground speed calculations, use different symbols and write down the answer key on your navlog for reference.
For example, use a dot for the first leg of flight, asterisk for the second leg, etc. Some of my learners have done well using colored pencils to make each mark in addition to the different symbols.
To determine ground speed, follow the directions printed in the E6-B. Put the index on the calculation side of the unit to the estimated ground speed calculated before the flight. The estimated ground speed is on the outer ring or A scale. Without repositioning the index, find the value for the distance covered on the A scale. The number beneath the value on the B scale is the time en route.
Let’s say you determined the ground speed will be 104. Place the index below 104 on the A scale. The first leg of level flight from checkpoint A to checkpoint B is a distance of 12 miles. Directly opposite the 12 on the B scale is 70. You know it didn’t take 70 minutes to cover that distance—that’s just silly—so the answer is seven minutes. That is your estimated time en route for that leg.
- READ MORE: Can You Fly With Expired GPS Database?
During the flight, place the E6-B in the side pouch with the calculation side facing you with the index placed on the ground speed you estimated—so in this case, 104.
Start the timer over checkpoint A—you notice that when you reach checkpoint B the timer reads eight minutes. Since it took longer, that means a headwind has been encountered. To determine the new ground speed, rotate the B scale until 80 (8) is under the 12. The index is now on the new groundspeed of 90.
Leave it there and in the pouch. You should be able to glance at it and determine ground speed. For example, the next leg is 14 miles. The B scale indicates it will take you approximately nine and a half minutes.
Practice with the E6-B on the ground (both mechanical and digital) until you don’t have to focus so much on the manipulation to discern the answers. Especially with the mechanical one, with practice you should be able to glance at it and determine the time en route.
Ask us anything you’ve ever wanted to know about aviation. Our experts in general aviation, flight training, aircraft, avionics, and more may attempt to answer in a future article. Email your questions here.
