Flapless approach with excess speed: float, balloon and the go-around decision
You are flying a Piper PA-28 on a flapless approach because the flap motor has failed in the up position. The aerodrome has a 1,200 m paved runway, dry, at sea level, wind calm. The POH gives a flapless approach speed of 75 KIAS, and a normal landing distance over 50 ft of 1,600 ft; flapless, allow about 30 per cent more. On final you are high and fast, and you cross the threshold at 88 KIAS instead of 75. You close the throttle over the threshold and the aircraft floats, still about 5 ft above the surface, past the first 2,500 ft of runway. Trying to force it down, you make a quick aft movement of the control column and the aircraft climbs to about 15 ft before settling again.
1. Explain why crossing at 88 KIAS instead of 75 costs so much runway on a flapless approach.
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Energy. Kinetic energy varies with the square of speed. Going from 75 to 88 KIAS is a 17 % speed increase and about a 38 % increase in kinetic energy that must be dissipated after the aircraft is on the ground - and, before that, several hundred feet of float while the excess is bled off.
Ground effect. Within about one wingspan of the surface, the wingtip vortices are suppressed, induced drag falls, and the wing can produce the same lift at a lower angle of attack. The aircraft therefore keeps flying at a height where a pilot expects it to settle. At 5 ft in ground effect with excess speed, the aircraft will float a long way.
No flaps. Flaps normally add drag and steepen the approach, letting you fly a lower attitude and a slower speed. Flapless, you approach at a higher speed and a flatter attitude, so the round-out and hold-off are longer even at the correct 75 KIAS.
Combined: the extra 13 kt plus ground effect plus no flap drag is why the aircraft was still airborne at 2,500 ft.
2. Explain what produced the climb to 15 ft and how it should have been corrected.
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The cause. The quick aft movement of the column raised the angle of attack sharply. Lift is proportional to the square of speed and to the lift coefficient, and at 80 kt or so the wing already had more than enough lift for the weight; increasing the angle of attack momentarily pushed lift well above weight, so the aircraft climbed. This is a balloon, and it is a pilot-induced oscillation, not a gust.
What happens next. The climb costs airspeed. As speed decays the wing can no longer support the aircraft at that attitude, and the aircraft drops back - often firmly, sometimes onto the nosewheel first.
The correction.
- Relax the back pressure and let the aircraft settle; do not push forward sharply, which risks a bounce and a porpoise.
- Hold the height with small power changes, not with elevator jabs, and keep the attitude constant once the aircraft is descending.
- Accept a firmer touchdown than usual; a firm landing on the mainwheels is far safer than a float followed by a balloon.
An aft jab of elevator at 5 ft is the classic way to turn a long landing into a damaged one.
3. At the point where the aircraft settles again, roughly 2,600 ft down a 1,200 m runway at about 80 KIAS, what do you do? Justify the numbers.
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Go around.
The numbers. The runway is 1,200 m, about 3,940 ft. At the settle point roughly 1,340 ft remain - about 34 % of the runway. At 80 KIAS on the ground you cover about 135 ft per second, and the aircraft still has to touch down, decelerate and stop; a flapless landing with no headwind at that weight needs over 2,000 ft from the 50 ft point even flown well. There is no configuration in which the remaining distance is adequate, and the balloon has already cost the energy margin.
The go-around in a flapless PA-28.
- Full power, carburettor heat cold, and hold the nose attitude to prevent a pitch-up.
- Accelerate to about 75–80 KIAS and establish a positive rate of climb; there is no flap to retract, so nothing else changes the configuration.
- Climb straight ahead to a safe altitude before turning; the runway is clear and there is no obstacle pressure.
- Fly the next approach at 75 KIAS with the aiming point moved slightly down the runway, so that the round-out begins with the throttle closed at the right speed rather than being forced.