Stalling: the warning signs and the recovery

What a stall is: an angle, not a speed

The wing makes lift in proportion to its angle of attack (the angle between the wing and the air flowing towards it) and to the square of its speed. Raise the angle and you get more lift, up to a point. At the critical angle, usually somewhere in the mid to high teens of degrees for a light aircraft wing, the airflow can no longer follow the upper surface. It breaks away, the lift falls and the drag rises sharply. That is the stall.

The stall speed in the flight manual is simply the speed at which the wing reaches that angle when it is carrying exactly the aeroplane’s weight: wings level, 1 g, at a stated weight and flap setting. Ask the wing for more lift, by pulling round a turn or out of a dive, and it reaches the same angle at a higher speed. That is why you can stall at any airspeed and in any attitude, including nose-down. Airspeed is a useful guide, but the angle is what matters.

The stalling trainer on this site flies a Cessna 172 at 2,400 lb. Its wing stalls at 17.5° clean and 14.5° with full flap, which gives a stall speed of 50 knots clean (the bottom of the green arc) and 41 knots with full flap (the bottom of the white arc). The trainer shows the angle of attack as a dot climbing a lift curve, so you can watch the wing approach the top of the curve and fall off it.

The symptoms of an approaching stall

In the classic power-off stall entry, where the pilot holds the height while the speed washes off, the warnings arrive in a fairly reliable order:

• The airspeed decaying, and the nose getting higher and higher to hold the height.
• The controls going soft and slow to respond, needing bigger movements.
• Less noise, with the throttle closed and the airflow slowing.
• The stall warner, a horn or buzzer triggered by a vane or reed on the leading edge, set to sound a few knots before the stall.
• Buffet, felt through the airframe and the controls as the airflow breaks up.
• Then the stall itself: the nose drops whatever you do with the control column, the aeroplane sinks, and a wing may drop.

Not every stall gives you all of them. In a turn, with power on, or when the pilot pulls suddenly, the speed and attitude cues may be missing and the warner and buffet may come only moments before the break. Treat the warner and buffet as the definite signs, and act on them.

How to recover from a stall

UK teaching, in line with current FAA and EASA guidance, puts one action ahead of everything else: unstall the wing. Before practising stalls in the aeroplane, UK students fly the HASELL checks (height, airframe, security, engine, location, lookout) and practise high enough to leave plenty of room; the trainer starts every demonstration at 4,000 feet.

1. Reduce the angle of attack. Move the control column forward, far enough to unstall the wing and no further. The buffet stops and the controls firm up.
2. Keep it in balance with rudder, and leave the ailerons alone until the angle of attack is reduced.
3. Level the wings with aileron, once the wing is unstalled.
4. Full power, smoothly, holding the nose against the pitch-up and using the rudder needed to keep the ball in the middle as the slipstream and torque yaw it.
5. Ease out of the descent as the speed builds, gently enough not to stall again (the secondary stall), and settle into a climb at the climbing speed.
6. Clean up and climb back to your original height, raising any flap in stages as the speed allows.

Here is that sequence in the trainer’s own model: the clean stall entry, wings level throughout, with the recovery started at the moment the nose drops. With no wing to pick up, the power follows straight after the column. Watch the angle of attack rather than the speed.

This is the order in the UK CAA’s safety leaflet on stalling, and the FAA’s handbook gives the same one (nose down, then wings level, then power), adding items for larger aircraft such as disconnecting the autopilot. Your aircraft’s flight manual has the final word on its own type.

Recovering at the first symptom costs almost nothing. The trainer shows this directly: its full clean stall, which holds the aeroplane stalled for a few seconds before recovering, loses three or four hundred feet before it is climbing again, while the same entry recovered at the stall warner loses under a hundred.

Try it: Open the stalling trainer, press Show me, and compare “The clean stall” with “Catching it early”

Why stall speed rises in a turn

In a level turn the lift is tilted, so the wing must make more of it to hold the height. The ratio of lift to weight is the load factor, and in a level turn it is 1 divided by the cosine of the bank angle. The stall speed rises with the square root of the load factor.

In the trainer’s aeroplane that means 50 knots wings level, 53 knots at 30° of bank (1.15 g), 59 knots at 45° (1.41 g) and 70 knots at 60° (2 g). The 60° figure is worth remembering as a rule of thumb: 2 g, and the stall speed up by 41 percent, because the square root of 2 is 1.41. It is the same angle of attack every time; only the speed at which the wing gets there changes.

Try it with the flap down too, and see how little margin a steep turn leaves.

The same logic covers a sharp pull out of a dive. Any time you load the wing, it will stall at a higher speed than the number marked on the airspeed indicator. This is often called an accelerated stall.

Flap, power, weight and centre of gravity

Flap

Flap changes the wing’s shape so it makes more lift at every angle of attack. It stalls at a slightly smaller angle, but the extra lift more than makes up for that, so the stall speed falls: in the trainer, from 50 knots clean to 41 knots with full flap. The nose is also noticeably lower at the stall, which is a trap on the approach, because the attitude looks less alarming.

Power

With power on, part of the weight is carried by the upward-tilted thrust and the slipstream keeps air moving over the inner wing, so the indicated stall speed is a little lower. The nose is much higher at the stall, the propeller effects yaw the aeroplane hard, and a wing drop is more likely. The power-on stall is the one that catches pilots on a badly flown go-around or a steep climb-out.

Weight

A heavier aeroplane needs more lift, so it stalls at a higher speed: the stall speed rises with the square root of the weight. Flight manuals usually quote it at maximum weight. Ice, frost or dirt on the wing also raise it, sometimes by a large margin, because they make the airflow separate at a smaller angle.

Centre of gravity

With the centre of gravity (CG) forward, the tailplane has to push down harder to hold the nose up, so the wing carries extra load and the stall speed is slightly higher. An aft CG lowers the stall speed a little but makes the aeroplane less stable in pitch, easier to stall by accident and harder to recover, which is why the aft limit matters so much.

Wing drop, and why aileron can make it worse

The two wings rarely stall at exactly the same moment. If the aeroplane is yawing, or is out of balance with the ball off centre, one wing will be at a slightly higher angle of attack and will stall first. It loses lift and drops.

The natural reaction is to pick it up with aileron. On the dropping wing, that lowers the aileron, which increases the angle of attack on a wing that has already passed its critical angle. It can stall that wing further, and the extra drag of the lowered aileron yaws the nose towards it. Stall plus yaw is how a spin starts.

So the recovery for a wing drop is the standard one, with the emphasis on rudder: column forward to unstall the wing, enough rudder to stop any further yaw, and only then roll the wings level with aileron, once the wing is flying and the aileron works normally.

Stalls in the circuit: the base-to-final turn

Many fatal stall accidents in light aircraft happen low, often in the circuit, where there is no height to recover. The base-to-final turn is the classic case. The pilot overshoots the centreline, feels the turn is too slow, and adds rudder towards the runway to tighten it without steepening the bank. The skid raises the inside wing’s angle of attack, the growing bank gets held off with opposite aileron, and the pilot pulls back to stop the nose dropping. That crossed-control state can stall the inside wing first and roll the aeroplane sharply towards the ground.

The cure is to fly a well-judged circuit (see the circuit pattern guide), keep turns balanced with the ball in the middle, keep the bank moderate, and if you overshoot the final turn, go around rather than tighten it. A strong tailwind on base makes the overshoot more likely.

Try it: In the stalling trainer, run “Stalling in a turn”: a 30° turn with power off and the height held, as if the turn onto final had been overshot

From stall to spin

A spin needs two things: a stall and yaw. With one wing more deeply stalled than the other, the aeroplane autorotates, rolling and yawing round a steep, slow descent, and it loses height quickly. Recovery takes a deliberate technique of its own, typically throttle closed, ailerons neutral, full rudder opposite to the yaw, then the control column forward until the rotation stops. The aircraft’s flight manual gives the exact procedure, and it varies between types.