VSI – Use a fortune teller to improve your flying

Most of our instruments tell us where we are – not where we are going to be.  For example, the altimeter tells us we are at 7000 feet or the airspeed indicator tells us we are at 120 knots.  However, one of our instruments can see into the future. No, this is not a fancy computer with lots of data, but a simple instrument which almost never fails. It is the vertical speed indicator (VSI).

This often ignored and sometimes scorned instrument can truly make you a more precise and smoother pilot. For example, if you are trying to hold altitude and you see the vertical speed indicator showing a 200 FPM descent, guess what?  I can now predict that in 30 seconds you will be 100 feet off your altitude. See how it predicts the future? So if you heed this prediction and make a little correction, you will maintain your altitude. That is one way we can use a fortune teller to improve our flying.

As an instructor it is painful to watch a pilot doing slow flight and have the altitude and speed on for the moment, but not realize that the vertical speed is showing 200 or 300 FPM down. They seem so proud to be on the numbers but are unaware that if they don’t do something soon they will be out of limits. So, as we sink slowly below the PTS limits, they add a little power, but usually not enough to get that VSI needle pointing back up. Finally after we are well below our altitude they add enough power to get a climb going and guess what, here we go right through our altitude and up beyond the limit on the other side. Using the vertical speed as a fortune teller in this maneuver tells you where that altimeter will be in a minute or two. Good information to know. Watching the altimeter only tells you what’s already happened.

Same thing works on steep turns. If you establish a pitch attitude that gives you zero on the vertical speed indicator, you will hold your altitude. While pitch attitude is the primary focus on steep turns, the vertical speed indicator will still predict where you will soon be if nothing changes.

When making an approach with a glide slope (GPS or ILS), the vertical speed indicator is essential to staying on the glide slope. Again it will predict deviations before they are displayed on the glide slope indicator. If the required descent rate is 500 FPM and I notice that the vertical speed has just changed to 200 FPM, I can predict the next thing that will happen is that I will start getting high on the glide slope. If I recognize that the vertical speed is not correct and fix it before the glide slope needle moves, I don’t have to make two corrections. One correction to get back on the glide slope and another to return to the proper rate of descent.

We all know that it takes a constant descent rate to stay on the glide slope and the one instrument in the cockpit that tells us that information is the vertical speed indicator. When I began to realize that the vertical speed indicator was great at predicting where the glide slope needle was going to go next, my ILS approaches got much better.

So why don’t pilots pay more attention to the vertical speed? Maybe it is because there instructor told them not to pay any attention to it because it has a lag in its response. I was told that on my first lesson and it took me about 30 years of flying to realize that instructor was wrong. Yes, there is a small lag in the vertical speed indicator but it still predicts the future better than any other instrument I know of.

So if you want to stay ahead of your airplane, learn to get more use out of the instrument that predicts the future.

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