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Home » John E. McLain

More Of This and That

By John E. McLain (January 2002)

Last month I discussed some flying concepts I considered important, but not substantive enough to warrant a complete article. I would like to continue with more of these kinds of ideas for improving the safety of flight and/or making life easier for you, the pilot.

First off, here is a little trick to help answer one of aviation’s most frequently asked questions: When will we get there? Without the help of GPS or some other fancy electronic device, many pilots find it difficult to provide a speedy, accurate reply. So, here is a quick way to figure the time it will take to cover a given distance, based on ground speed.

Tell me: What do the following ground speeds have in common: 60, 100, 120, 150, 180 or 200 kts or mph? Forgetting zeros and decimals, they all have a devisor or multiplier that equals six. For example, 60 divided by or multiplied by one equals 6; 100 multiplied by six equals six (remember, forget the zeros and decimals); 120 multiplied by five or divided by two equals six. Get the idea?

Now, here is what you do. Let’s say you want to know how long it will take to go 40 miles. If your estimated ground speed is 60 mph, multiply or divide the distance by one and you get your time to cover 40 miles, which is 40 minutes. In the case of 100 mph, multiply the distance by six and you get 24 minutes. For 120 mph divide by two or multiply by five and you get 20 minutes. Now, quick, how long to go 40 miles at 150 mph? The answer is 16 minutes and four is the magic number (150 multiplied by four equals six).

Another area where pilots should be a more knowledgeable concerns the airspeed indicator. Just how accurate is it? Perhaps some of you have noticed the FAA’s fascination with a speed of 1.3 Vso, Vso being the stall speed in landing configuration.

The Category A instrument approach speed is 1.3 Vso or 91 kts or less. Why not just Vso of 70 kts? Are they the same? Or, why is the recommended approach speed for a short field landing no more than 1.3 Vso? Well, the answer is simple. When an airplane is certified, the airspeed indicator only has to be accurate between 1.3 Vso and the never exceed speed (red line), so let’s briefly discuss calibrated and indicated airspeed.

Simply put, calibrated airspeed is what the airspeed indicator should read; indicated airspeed is what it does read. The difference between the two is instrument error. Between 1.3 Vso and never exceed speed (red line), this error can be no more than 3 percent or 5 kts, whichever is greater. You can find this information in FAR Part 23, paragraph 23.1323.

It might seem like this would be useful only in a game of aviation trivia but it points out that the airspeed indicator is not 100 percent accurate, especially below 1.3 Vso.

Years ago, people were taught to fly by the “seat-of-their-pants.” Now the stress is on flying “by-the-numbers.” The latter is fine, given the precision of modern instruments. However, at airspeeds below 1.3 Vso pilots still must develop a feel for the airplane. This was demonstrated to me on a recent private pilot flight test. I asked the applicant to do a power off stall. The practical test standards require that in the performance of a stall, the applicant announce the first indications of the stall and then continue to increase the angle of attack until the stall occurs.

Well, he flew by the numbers. When the airspeed indicator showed 5 kts above the published stall speed, he announced an imminent stall. When it pointed to the stall speed, he announced the stall and proceeded to perform a stall recovery. Unfortunately for him, the airplane had a way to go before the stall would have occurred. When he followed the same procedure in performing a power on stall, I was convinced he would not be able to recognize an actual stall until it was too late. We returned to the airport and a notice of disapproval.

I suggest to all my readers that they try the following. Plan an instructional flight. I suggest the use of an experienced instructor, but you can do it on your own as long as you’re careful. Determine what 1.3 Vso is for your airplane. Slow the airplane below this speed, with the power at idle, then cover the airspeed indicator. Now, change pitch attitude and note the reading on the vertical speed indicator. It will, eventually, show a descent. Get a feel for what various descent rates are. With a little practice you should be able to “feel” a normal descent rate of 500 fpm or an excessive descent rate of more that 1,000 fpm. Repeat this exercise at various flap and power settings. Do this until you are confident in your ability to “fly by the seat of your pants” at low power settings.

Now you are ready for the ultimate test, and here is where I strongly suggest you have an instructor on board, or at least an experienced and competent safety pilot, the first few times you do it. Perform several takeoffs and landings with both the airspeed and vertical speed indicators covered up. When you can do this comfortably and safely, no longer will you need to worry about slow speed flight or landing if your airspeed indicator fails, and they do fail on occasion.

Here is one final suggestion. When you preflight your airplane, be sure to stand back 20 feet or so and look at the whole airplane. Just recently, I was told of an incident where a nose gear apparently had been damaged by a hard landing. Several people flew the airplane after that but did not catch the problem. Finally one pilot, as he was approaching the airplane, noticed the problem when he was about 50 feet away. The airplane was grounded immediately and the owner thanked his lucky stars he did not have to contend with the expense of a collapsed nose gear.