July 2007 Newsletter

Want to practice a single maneuver that can teach volumes about safely flying airplanes? Consider the steep turn -- perhaps the perfect training and proficiency maneuver.

Steeps turns are a required Task for all airplane pilot certificates -- Recreational, Sport, Private, Commercial and Airline Transport Pilot. The Practical Test Standards (PTS) for each certificate tell the examiner to evaluate candidates for their knowledge of steep turns, and for adhering to basic safety rules for the maneuver: Clear the area before beginning the steep turn and perform the maneuver at or above 1500 feet AGL. Specific completion standards for the steep turn vary slightly by certificate sought, as listed on this table:

That's an awful lot of good from what many consider a "circus trick" to be demonstrated on a checkride and never flown again. So let's look more closely at the steep turn.

A "Performance Maneuver"

The FAA's Airplane Flying Handbook (FAA-H-8083-3A) calls steep turns a "performance maneuver," in the same category as steep spirals, chandelles and lazy eights. The object of the steep turn (as a PTS maneuver) is to "develop the smoothness, coordination, orientation, division of attention, and control techniques necessary for the execution of maximum performance turns when the airplane is near its performance limits." Flown within PTS limits, the steep turn requires a pilot to balance bank angle, pitch attitude and in most cases power setting to accomplish the triple goals of altitude, bank and airspeed control. As such it's an excellent training maneuver; successful execution indeed demonstrates the pilot has total control of the aircraft.

When conducting initial or recurrent type-specific training in high-performance singles or light twins I have my student fly 360° steep turns both right and left early in the program, for reasons I'll come back to later. For most of my clients, it's the first time they've done steep turns since their last pilot checkride. But unlike the PTS, which requires steep turns be done in a specific way, I point out a few things and change the maneuver a bit here and there to show the true training benefit of the steep turn.

One thing I ask my students to note is the amount of back pressure needed to hold altitude in left-hand vs. right-hand turns. In a single-engine airplane or a twin without counter-rotating propellers, most pilots agree it takes a lot more "heft" to keep the nose up in a left steep turn when compared to one to the right. Why is this? When banked steeply to the left, the left-turning tendency of the propeller(s) is pulling the airplane downhill, requiring a greater elevator deflection to compensate. That means more control force for the pilot (or trim system), increasing drag and trying to unbalance the maneuver even more. In a right-hand turn, conversely, left-turning tendency is actually trying to reduce the bank angle, meaning the pilot needs to add a little more roll input but not nearly as much back pressure to hold altitude. The effect is more pronounced the greater the power and torque.

If you're lucky enough to be flying something like a deHavilland Tiger Moth or Chipmunk with an engine that turns "the other way," the effect is reversed. If you're flying a light twin with counter-rotating propellers, the control requirement will be the same in either direction of bank.

The important point here is that, especially in a left turn, a steep turn left unchecked will try to get steeper still.

Spiral Tendency

After my student has demonstrated the maneuver PTS-style and notes the differing control forces, I then use the steep turn to show the tendency of a stable airplane to enter a destabilizing spiral descent. To do this I have my student trim the airplane at or below published Va in a "clean" configuration (flaps and gear up). At a safe altitude (I try for at least 3000 feet AGL), I'll ask the pilot to put the airplane in a roughly 35° bank, then let go of the controls.

What does this tell us? In most airplanes, if the bank angle is allowed to get steep and the pilot does not apply the right amount of back pressure or opposite aileron, the aircraft will naturally and quite rapidly descend in an ever-tightening circle with a dramatically fast increase in airspeed and vertical speed. If the maneuver is begun at altitude, the pilot may be able to recover, but if not the airplane will develop a rate of descent in the thousands of feet per minute, and airspeed may quickly accelerate through the yellow arc to red line (Vne) and beyond. A steep turn is the genesis of the "graveyard spiral" and, in turn, is implicated in most in-flight break-ups when a pilot gets disoriented by turbulence or an inadvertent cloud penetration.

What else can this teach? Altitude loss comes rapidly in a steep turn, especially to the left. Where do we have the greatest number of traffic pattern accidents? Base turning to final, almost always a left-hand turn. What's considered one of the riskiest instrument maneuvers? A circling approach, which is by definition a low-altitude, close-in (read: tighter turns) traffic pattern in poor visibility, in almost all cases turns to the left. Just a little distraction in the turn to final or a circle-to-land maneuver and that airplane can descend that last 500 feet into terrain in a matter of seconds.

What did your primary flight instructor teach you about traffic pattern turns? "Keep the bank angle below about 20°." Why? In part, so if you're distracted you won't inadvertently spiral into the ground. I personally feel that many of the accidents we think of as "stall/spin" during the downwind-to-base or base-to-final turn may in fact be spirals that develop so quickly the pilot can't recover in the altitude available.

Accelerated Stalls

Bank angle of course has an effect on stalling speed as well. The angle of attack of an airplane's wing is determined by a number of factors, including indicated airspeed, airplane weight and load factors imposed by maneuvering. For a given set of conditions, the wing will consistently stall at the same indicated airspeed. It will stall at a higher indicated airspeed under g-loads imposed by steeps turns. If altitude is kept constant, stall speed increases at the rate shown in the table at right.

Stalls in steep turns happen at a much higher indicated airspeed than the same stall in wings-level flight. For this reason they are called accelerated stalls. For example, an airplane that stalls at 50 knots indicated in level flight and zero bank angle will stall at about 53 knots in a 30° bank. Enter the realm of the steep turn, however, and that same airplane will stall at about 61 knots in a 45° bank, and 71 knots indicated airspeed in a 60° bank. No wonder our instructors teach us to keep bank angles shallow in the traffic pattern!

The Airplane Flying Handbook advises that accelerated stalls should be practiced at no greater than approximately 45° bank angle -- a steep turn. The Commercial PTS calls for 55° bank ±5°. Why 55°? The FAA considers bank angles beyond 60° to be "aerobatic" maneuvers, with additional aircraft certification requirements and things like required parachutes. Setting the standard at 55° permits the FAA to provide a +5° tolerance and still not enter the realm of "aerobatic" flight.

The Airplane Flying Handbook also recommends that speed be no greater than the airplane's published design maneuvering speed (Va) or other speed recommended by the airplane manufacturer -- check the Limitations section of the Pilots Operating Handbook.

Caution: Cross-controlling (bank one way, rudder the other) in an accelerated stall is a quick way to get into a spin, so accelerated stalls are best practiced with an experienced instructor pilot who knows the characteristics of the airplane you're flying.

If you bank excessively in the pattern and you try to hold altitude, the stalling speed will increase dramatically. If you cross-control the airplane in a steep turn, you can snap over into a spin with little warning. This is even more reinforcement of our instructor's admonition to keep the bank angle shallow in the traffic pattern or in a circling approach.

Instrument Scan And Proficiency

Steep turns are often practiced "under the hood" during initial instrument training, but they do not appear in the instrument PTS, nor is there any requirement to practice them at all. Nonetheless I include steep turns early in my initial and recurrent training (told you I'd get back to "why") because I've found they are one of the best indicators of the quality of a pilot's instrument scan. Throughout a steep turn the qualities of pitch, altitude and heading are all changing and it's up to the pilot to quickly detect deviations, decide what effect they will have, and adjust the yoke and power to hold altitude while keeping the bank and airspeed constant. That sounds a lot like the credo of the instrument pilot: scan, interpret, and aircraft control.

I actually like to deviate a little from the PTS-style steep turn by leaving power set as it was during turn entry. This means airspeed will begin to decay during the steep turn, making the maneuver even more dynamic and requiring the pilot pick up and act upon deviations even quicker to stay within the remaining PTS criteria. Practicing steep turns this way forces a pilot to scan the instruments and make minute control corrections very rapidly if there's any hope of holding altitude and rolling out on assigned heading. If a pilot's scan is slow it'll show up right away in steep turns under the hood; it tells me up front what my student will have to work on to pass an instrument proficiency check (IPC) and therefore helps me orient the rest of my course. I've also found a few view-restricted steep turns are the quickest way to knock the rust off an out-of-practice instrument pilot's scan.

What about partial panel flight? We now know that getting into a steep turn makes all sorts of bad things possible. In instrument flight, in fact, all turns at greater than standard rate (about 20° bank angle at 120 knots, and just under 30° bank if you can fly around 180 knots) are by definition a "steep" turn. Avoid the pitfalls of steep turns by keeping your bank angle shallow when flying by reference to instruments; if your attitude indicator has failed, follow your CFII's advice to hold all turns at about half-standard rate ... a very shallow bank angle indeed.

Steep Turns And Engine Failures?

Steep turns even teach us about the dreaded "engine failure on takeoff" scenario in single-engine airplanes. Aerodynamic theory demonstrates that it may be possible in a 45° bank to lose power at as little as about 800 feet above ground level, turn around and line up for landing on the departure runway (albeit landing in the opposite direction). Knowing what you now know about steep turns, however, you might decide that the risk is not worth it. A steep-banked turn, executed any way other than perfectly, can cause an incipient spiral that robs what little altitude you have in the little time you have before impact. Pull back to resist the descent and stall speed increases up to 22 percent in that 45° banked turn. In most cases you simply can't win -- which is why the FAA has dubbed this ill-advised maneuver "the impossible turn."

Let's review what we can learn from steep turns:

So go up and practice steep turns. They may be the perfect proficiency maneuver.

Fly safe, and have fun!