Features

August 2019 Issue




Finding Pivotal Altitude

If you absolutely, positively have to fly eights on pylons, you need to know how to do this.

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A long-time pilot-friend of ours tells a story about his first check ride for the commercial certificate. Everything was going relatively well until the examiner asked him to perform the eights on pylons maneuver. His response was something along the lines of, “Yes sir, thank you, sir, and what altitude would you like, sir?” The examiner ended the check ride and told him to come back after talking with his instructor about pivotal altitude. When he did, he learned that the correct pivotal altitude for a given groundspeed allows a banked line of sight from the cockpit directly parallel to the lateral axis of the aircraft to the pylon, a stationary object on the ground. Our friend went on to be one of the first pilots to fly the Airbus A300 in the U.S., for Eastern Airlines.

Most commercial applicants really, really don’t like the ground-reference and performance maneuvers. They know—or have a pretty good idea—that lazy eights and chandelles have little practical application in the flight levels, with steep spirals and steep turns important only when you want to be on the ground right now. And perhaps the commercial maneuver getting the least respect/greatest dislike is eights on pylons.

The basic maneuver is to fly a horizontal figure eight over the ground, almost circling easily observed surface features—the pylons—for the loops before leveling the wings and maneuvering to the second pylon. Turn in the opposite direction around it and fly back to the first pylon. Another way to think of eights on pylons is as eights around pylons, “except altitude is varied to maintain a specific visual reference” to them, according to the FAA’s Airplane Flying Handbook, (AFH) FAA-H-8083-3B. Rinse, repeat until the examiner calls it off. Sounds simple, right?

The maneuver’s quality is judged by the pilot’s sight picture during the horizontal loops. The idea is to establish a sight picture of the pylon relative to the airplane’s wing and maintain it as you turn about the pylon. In other words, line up the pylon with something like the second row of rivets aft of the wing’s leading edge and keep it there, through more than 180 degrees of turn. Use aileron, rudder and pitch to manage the sight picture. And don’t forget to roll out of the turns in time to head off to the other pylon.

Although the commercial airman certification standards (ACS) and the AFH don’t discuss using power during the maneuver, that can quickly get out it of hand. Even if you pull it off, it’s unlikely to earn you any Brownie points with the examiner. The ACS does say the bank angle should be no more than 40 degrees. The examiner wants to see the applicant make “corrections so that the line-of-sight reference line remains on the pylon” and maintain the pylon’s sight picture at the appropriate pivotal altitude, while avoiding slips and skids. You also need to “divide attention between accurate, coordinated airplane control and outside visual references.”

The maneuver gets complicated thanks to the wind and how the sight pictures differ when viewed along the two different lines of sight—parallax. Each turn presents one of two different sight pictures, and what worked well to perform the maneuver when turning left may well require the opposite in control inputs when turning right.

Altitude And Groundspeed

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By now, you might be thinking, “This is a cinch. When do we start?” Remember when we mentioned how wind complicates things? Presume you have a five-knot wind. If you align the pylons with the wind, you’ll see a 10-knot groundspeed difference while performing the loops around each one. You’ll see crosswind effects if you choose pylons aligned perpendicular to the prevailing wind.

That’s important because groundspeed determines how much you need to bank during the loops. As groundspeed increases, the pylon will move aft in relation to that line of rivets you’re looking at for your sight picture. Naturally, it will move forward when slowing. Likewise, You’ll want a more shallow bank when groundspeed is lower, like when flying into the headwind while trying to maintain the same sight picture, and a steeper bank—still not to exceed 40 degrees—with a tailwind during the maneuver.

You’re probably also wondering about this article’s title, and altitude’s effects when flying eights on pylons. The table and graphic on the opposite page can help us find the Mama-bear altitude at which we want to fly the maneuver, but only at our nominal groundspeed. If we want to fly eights on pylons at 100 knots groundspeed, for example, we might need to do some flight planning to learn the anticipated winds and then come up with the airspeed and power setting that will produce the desired groundspeed.

If we do plan to fly the maneuver at 100 knots groundspeed, we’ll ideally want to be at that value when we’re directly downwind—and perhaps flying in a crosswind—while circling the pylon, accepting the groundspeed fluctuations. The good news is that, unless the wind at 1000 or so feet agl is really honking, we’re only talking about a few knots difference when circling the pylon. If the wind is honking, maybe it’s not the best day to do the maneuver.

There’s a formula for calculating pivotal altitude used to create the table at the bottom of the opposite page:

To use the formula, square the desired groundspeed, then divide by 15 (if the groundspeed is in miles per hour) or divide by 11.3 (if the groundspeed is in knots). Then add the mean sea level (MSL) altitude of the ground reference.

Since flying eights on pylons is designed to require maneuvering in all three of the airplane’s axes, altitude will vary from the pivotal altitude during each loop. Ideally, you should be at the pivotal altitude when at the chosen groundspeed, and either climbing or descending—while steepening and shallowing the bank—to maintain the desired sight picture. You’ll want to be slightly below pivotal altitude when groundspeed is low, and slightly above with a tailwind.