Predictable and Unpredictable

Written by Micheal Busnitz, Chief pilot

Predictions and those who make them are many. Folks make predictions about the weather, stock markets, politics, sports teams, crop yields, and when California will fall off the North American continent. You name the subject, and I predict it is likely that someone has made a prediction about it. Many of those predictions are incorrect. Life is filled with the predictable and unpredictable.

It's spring time. Birds are returning. Flowers are blooming. The busy seasons of spring, summer, and fall lie ahead. Who knows whether the predictions and hopes for our work, families, and ministries will come to fruition? How glorious is it that we do not need to enter a new season relying on fallible predictions. Our hope rests with the eternal, sovereign God, who says of Himself:

         For I am God, and there is no other;
         I am God, and there is no one like Me,
               Declaring the end from the beginning,
         And from ancient times things which have not been done,
         Saying, ‘My purpose will be established,
         And I will accomplish all My good pleasure’;
-Is 46:9–10

His purposes will be established, and His good pleasure accomplished to the supreme joy of everyone who has yielded to His authority.

As in all of life, flying airplanes includes unpredictable events. I had one of those recently. Are you up for a game? Before reading the caption below, can you figure out what is wrong with this picture?

Through the window you can see that we are in flight...but the airspeed indicator (speedometer) is pegged on 0. That is not what you would predict ... or hope to see!

I dropped off a missionary and departed. The takeoff was normal, including the "airspeed alive check," when the needle comes off its peg during acceleration. After liftoff, I glanced at the airspeed indicator for flap retraction speed. And there it was: no airspeed!

Airplanes are flown by set speeds: climb speeds, configuration speeds, stall speeds, cruise speeds, approach speeds, etc. A properly working airspeed indicator is necessary to the safety of flight. Fly too slowly, and you stop flying, if you know what I mean.

Without airspeed indication, standard practice is to resort to known power settings and pitch attitudes which result in the desired airspeeds. In other words, hit the gas and don't point the nose too high!

I started investigating to see why there was no airspeed indication.

For those who don't spend their life staring at a wing: the probe sticking straight forward is the Pitot Tube. (It's a French word. Leave off the second "t" and you are saying it correctly.)

Air rushes into the pitot tube through a hole in the front. The incoming air exerts pressure which is converted and displayed in the cockpit as airspeed. In the picture, you see that a small tab is covering the front of the pitot tube, blocking the flow. If no air is going in, there will be no airspeed indication. And there wasn't!

(Bonus paragraph for the mechanically curious: That tab keeps bugs and other debris from clogging the hole while the aircraft is on the ground. As the airplane accelerates, increasing air pressure on the top of the tab raises the tab out of the way. Obviously, that did not happen.)

We flew the established power settings and pitch attitudes to the destination, cheated a little higher on the power during the approach to avoid a stall, and landed without incident. When I inspected the pitot tube, sure enough, the tab was lodged down and slightly to the right. A small portion of the hole was exposed. That explains the initial "airspeed alive" indication during the takeoff roll. But once airborne, the angle of attack changed, and all airspeed indication vanished.

What caused the cover tab to become lodged? As I was taxiing out for takeoff, the winds were gusty. One particularly strong gust from the left rocked the airplane to the right. My best guest is that the same gust pivoted the tab slightly to the right and lodged it there. That was a first. Thank you for praying for safety in the predictable and unpredictable ins-and-outs of flying. God answers!