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Eights on Pylons

Every other ground reference maneuver asks you to hold a shape over the ground. This one asks you to hold a line of sight, and lets altitude do the work.

Ground Reference Maneuvers — FI.X.D

Why you fly it

Choose a silo. Put the reference line off your wing on it and hold it there while the airplane goes around, then roll out, cross to a second silo and do the same in the other direction. There is no radius to protect and no ground track to draw. The airplane flies whatever path the sightline demands, and the figure eight is what falls out of it.

What makes it work is altitude, not bank. There is one height above the ground at which the sightline off your wing stays pinned to a fixed point while you turn around it, and that height depends on how fast you are moving across the ground. Flying it builds a feel for how groundspeed, bank and turn radius are tied together. It also demands real divided attention: holding a visual reference, staying coordinated, minding the airspeed and keeping a landing spot in mind, all at once and all of it close to the ground.

It is not an academic exercise. Aerial photography, pipeline patrol, agricultural work and search flying are all the same skill: circling a point at low altitude while something else has your attention. That is why it sits on the commercial certificate.

Pivotal altitude is the whole maneuver

Pivotal altitude is the height above the ground at which a line extending from your eye out along the wing appears to pivot on a fixed ground point as you turn. Above it, the airplane turns faster than the sightline to the pylon needs to sweep; below it, the airplane turns too slowly to keep up with it. Either way the reference line will not stay on the pylon, and the direction it slides is what tells you which side of pivotal altitude you are on.

It comes out of groundspeed alone: pivotal altitude in feet AGL = groundspeed in knots, squared, divided by 11.3. In miles per hour, divide by 15 instead.

Notice what is not in that formula: bank angle, weight, distance from the pylon. Two airplanes at the same groundspeed have the same pivotal altitude however steeply either is banked.

Notice also that it is groundspeed, not indicated airspeed. That is the entire reason the maneuver is hard. Hold one airspeed and one power setting all the way around a pylon in a wind and your groundspeed still changes continuously, so the altitude you need changes with it. At 100 knots true in a 10-knot wind, pivotal altitude runs from about 717 feet headed into the wind to about 1,071 feet headed downwind — over 350 feet of gentle climbing and descending inside every turn.

The reference line

The reference is an imaginary line from your eye, parallel to the airplane's lateral axis, out to the pylon. Pilots call it the wingtip, and it often falls near the wingtip, but where it really lands depends on your seat position and the wing. Find the spot that works on your airplane and use the same one every time — a reference that moves is no reference.

Before you start

Most schools teach some flow to run before a maneuver. CHAPS is one common version of it, a training convention rather than anything the FAA publishes, so fly whichever one your instructor uses — what matters is that the same items get covered every time:

Add the regulation to that list. 14 CFR 91.119 sets the floors you have to stay above: over a congested area, 1,000 feet above the highest obstacle within a horizontal radius of 2,000 feet; over other than congested areas, 500 feet above the surface; and over open water or sparsely populated areas, no closer than 500 feet to any person, vessel, vehicle or structure. Pivotal altitude knows nothing about any of that. At the low end of trainer groundspeeds it works out near 500 feet AGL, which leaves no margin at all over the wrong ground. Run the number before you go, and if it falls below what the regulation allows where you meant to fly, it is the ground you change, not the altitude.

Setting up and flying it

Pick two pylons on a line roughly perpendicular to the wind, at about the same ground elevation, over sparsely populated ground, well clear of towers, wires and congested areas, with somewhere to put the airplane down nearby. Space them so you get three to five seconds of straight-and-level flight between the turns.

Enter on a diagonal to the line joining the pylons, heading downwind, where groundspeed and therefore pivotal altitude are highest. Roll into the first turn as the reference line comes up on the pylon — there is no fixed bearing to wait for, the sightline itself tells you when — and set whatever bank holds it there. Bank should not have to exceed 40 degrees; if it does, your pylons are too close together or your entry was too tight.

Fly the half turn, roll out wings level on the diagonal toward the second pylon, crab for the wind on that short leg, and roll into the opposite turn. The pattern is the eight; the work is holding the sightline.

Reading the pylon

The pylon is your altimeter, and the Airplane Flying Handbook has you read it by watching the reference line rather than the pylon. If the reference line appears to move ahead of the pylon, you are below pivotal altitude and the correction is to increase altitude. If the reference line appears to move behind the pylon, you are above pivotal altitude and the correction is to decrease altitude. Work a few feet at a time, and expect to be correcting continuously as groundspeed changes around the turn.

Leave the power where you set it while you do this. Pivotal altitude is set by groundspeed, so a power change moves the very altitude you are climbing or descending toward, and you spend the turn chasing a target you keep pushing away. Hold the airspeed and power you set up with and change height with small pitch inputs instead.

What you must never do is chase the pylon with rudder. Yawing the airplane will swing the sightline onto the pylon and it will look, for a second, like it worked. It has instead put you in a slip or a skid in a banked turn at low altitude, which is the exact set of conditions that turns a stall into a spin with no room to recover. Keep the ball centered and fix the altitude instead.

What goes wrong

The most common failure is computing or holding the wrong altitude, which shows up as a sightline that never settles. Close behind it is forgetting the wind on the legs between pylons, which distorts the pattern and leaves you rolling into the second turn from the wrong place. Then come the control errors: overbanking past 40 degrees and overcontrolling to fix it, rudder-only corrections, and rolling in late or out early.

Underneath all of them is task saturation. Staring at the pylon costs you the airspeed, the ball and the traffic; staring at the panel costs you the pylon. If you are fixated, or you have lost track of the wind or of where you would land, roll out, climb, and set it up again.

Where you meet it next

Eights on pylons is a commercial pilot maneuver, and flight instructor applicants demonstrate and teach it. On the checkride you will be asked to explain pivotal altitude before you fly it, and the examiner watches the sightline and the ball as much as the pattern.

It also settles something the rectangular course and turns around a point only hint at: in steady air, wind leaves your indicated airspeed alone while it changes everything you see out of the window. Shear and gusts are a different problem, and there the airspeed excursion is the whole hazard. Once pivotal altitude makes sense, why a base leg flown with a tailwind overshoots the runway needs no further explanation.

Fly the rectangular course and turns around a point again before your next lesson on this one, and read the steep turns lesson for the bank and load factor underneath it; all three are in the lesson index. If you are picking a day for it, the density altitude tool will tell you what your true airspeed is really doing, which is where your groundspeed — and so your pivotal altitude — starts.

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