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Steep Spirals

Your engine quits and you are directly over an airport. You are not short of options — you are short of a way to lose three thousand feet without leaving the field.

Performance Maneuvers — FI.IX.B

The reason it exists

Altitude is easy to lose in a straight line and hard to lose over one spot. Glide away from the field to burn off three thousand feet and you have spent the height that was going to bring you back. Circle at a gentle bank and you are still coming down too slowly to be finished before the wind carries you off the field. The problem was never the descent. The problem is making the descent without giving up the runway you already have.

The steep spiral is the answer to that problem. It is a gliding turn that sheds altitude quickly while the airplane orbits one point on the ground at a constant radius, so the field stays in sight off the wing and you arrive at pattern altitude still free to roll onto whichever final you like. Everything else in the maneuver — the constant radius, the bank that never stops changing, the three full turns — is practice for that descent.

What you are actually flying

A steep spiral is a constant-radius descending turn around a ground reference point, flown with the throttle at idle at your airplane's best glide speed from the POH. The FAA files it with the performance maneuvers rather than with the rectangular course and turns around a point, but the wind correction is borrowed whole from that family, and carrying both jobs at once is what makes it harder than either one alone: you are holding a circle over the ground, an airspeed, and a coordinated turn, all while the picture out the window changes every few seconds.

The commercial standard is at least three 360-degree turns, finished no lower than 1,500 feet AGL, holding your chosen airspeed within 10 knots and rolling out on a specified heading or reference within 10 degrees. Three is the minimum, not a fixed count — a fourth turn is not a deviation, but running out of height in the third one is. Those numbers set your entry altitude before you ever touch the throttle. Work upward from 1,500 AGL and add margin.

Constant radius, changing bank

The circle you are drawing is on the ground, and the wind does not care about your bank angle. On the downwind side of the circle your groundspeed is highest, so the airplane wants to swing wide and you need the steepest bank to hold the radius in. On the upwind side your groundspeed is lowest, the airplane wants to cut the circle short, and you shallow the bank out to let the radius open back up. Between those two points the bank is changing continuously, not in steps.

The bank must not exceed 60 degrees at the steepest point. That is a limit, not a target, and it costs more than it looks. Load factor rises with bank angle: in a level 60-degree turn the wing carries twice the airplane's weight, and stall speed rises with it — roughly 40 percent above the wings-level figure. The margin between your glide speed and the stall is thinnest exactly where the bank is steepest. If holding the radius on the downwind side is pushing you toward 60, the circle you picked is too tight for the wind — fly a bigger one.

Bank angle is also the reason airspeed wanders in this maneuver: every time you steepen, more of the wing's lift goes sideways and less goes up, so the pitch attitude that held best glide a moment ago no longer does. Pitch and bank move together the whole way around.

Flying it

1. Clear the area with clearing turns and pick a spot where the maneuver can be flown safely, well clear of congested areas and with a landing option underneath.
2. Choose an entry altitude that gives you three full turns above 1,500 feet AGL.
3. Configure per your POH — fuel selector, mixture, and whatever flap setting the POH gives for best glide.
4. Pick a prominent, distinct reference point and turn onto a downwind heading.
5. Abeam the point, apply carburetor heat if the airplane has a carburetor and the POH calls for it, bring the throttle to idle, and hold altitude while the airspeed bleeds off to best glide. Then lower the nose to hold that speed and trim for it.
6. Roll into the turn. This is the downwind side, so this is the steepest bank you will use all the way around.
7. Adjust bank continuously to hold the radius, coordinating with rudder, and keep the airspeed pinned as the bank changes.
8. Clear the engine at the completion of each 360 by advancing the throttle briefly, then return to idle.
9. After the third turn, roll out on the heading or reference you named, return the carburetor heat to cold, then add power and resume a normal climb.

Clearing the engine is not a formality. Several minutes at idle cools the cylinders faster than they would like and lets the plugs load up, and an engine you have neglected for three turns is exactly the one that will hesitate when you need power again. Do it on the downwind portion of each circle, where you have a moment to spare.

The same long descent is where carburetor ice collects. A carbureted engine at a closed throttle is the textbook setup for it, and the first thing it tells you is an engine that will not answer when you finally ask. Apply carburetor heat as the throttle comes back and leave it there through the descent, following what your POH says about prolonged idle — some airplanes want it on continuously, and a fuel-injected airplane has no carburetor heat to apply. Return it to cold before you add power at the rollout, so the engine gets cold dense air and full output for the climb.

What goes wrong

Most of the errors come from where your eyes are. This is a visual maneuver, and a pilot who flies it off the attitude indicator and the airspeed tape loses the circle entirely — the reference point drifts, the radius goes egg-shaped, and the traffic scan stops. Look outside, use the instruments to confirm, and keep dividing attention between the point, the airplane and the sky around you.

The second family of errors is pitch. Sloppy entries balloon the airplane or let it accelerate, and a pilot fighting a mistrimmed airplane through three turns will not have the capacity left to correct the bank for wind. Trim it once the glide is established and the maneuver gets much quieter.

The rest is a short list worth knowing by name: gaining altitude in the turn, failing to change the bank as the wind direction relative to you changes, uncoordinated flight with the ball out to one side, letting the airspeed drift away from best glide, becoming disoriented and losing the point, and rolling out somewhere other than the heading you called. The risk that ties them together is low-altitude maneuvering. You are descending in a steep turn with the power off, and the stall speed that applies is the one for the bank you are holding, not the wings-level number on the placard — so glide speed and coordination are what keep the airplane away from a stall it has no altitude to recover from.

Where you meet it next

On the commercial checkride the steep spiral sits in the same area of operation as steep turns, chandelles, lazy eights and eights on pylons, and it is the only one of them flown with the throttle closed — so the examiner is watching your glide speed as closely as your bank control, and your wind correction as closely as both.

It also shows up uninvited in the emergency approach and landing, because the moment you find yourself high over a chosen field, the steep spiral is how you fix it. The wind correction is the one you first met in turns around a point, flown steeper and downhill; the power-off judgment is what the power-off 180 grades at the runway. Practice it there, so that when the propeller stops you are not learning it for the first time. Those lessons and the rest are in Learn.