Go-Around at Low Airspeed with Full Flap
A low-wing single-engine aeroplane (MTOW 1,150 kg, wing area 16.2 m²) is on short final at 300 ft AGL, 65 KIAS, full flap (40°), mass 1,050 kg. VSO at MTOW is 52 KIAS. Headwind is 8 kt. The engine is at idle. A vehicle enters the runway and the tower instructs a go-around. The pilot applies full power and pitches to about +12°; within 4 seconds airspeed decays to 58 KIAS, the stall warning chirps intermittently, and elevator force is high. The pilot has not moved the flap lever. The runway is 1,800 m long, OAT 24°C, QNH 1013. The pilot's instinct is to raise all flap immediately and trim nose-down. The aircraft has a fixed-pitch propeller and no angle-of-attack indicator; the pilot is the only occupant.
1. Using the mass and VSO data, explain why 58 KIAS was an unsafe speed in this configuration. Show the calculation.
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At 1,050 kg the stall speed is not 52 KIAS. $V_{S0}\propto\sqrt{W}$, so $V_{S0}=52\sqrt{1050/1150}=49.7$ KIAS. At 58 KIAS the margin is 58/49.7 = 1.17 $V_{S0}$, well below the normal 1.3 $V_{S0}$ (64.6 KIAS). The aircraft was heavy enough and the flap setting high enough that the stall warning was giving valid information. The pilot’s pitch input and full flap drag had already eroded the speed margin; adding power did not instantly restore it because thrust takes time to overcome drag and the nose was held too high. The correct response is to lower the nose to maintain at least 1.3 $V_{S0}$ (about 65 KIAS) and accept a temporary altitude loss. Do not chase the stall warning with back pressure or trim.
2. Was the instinct to raise all flap at 58 KIAS correct? Explain the aerodynamic trade-off and give a flap-retraction schedule.
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Raising all 40° of flap at 58 KIAS would be wrong. Retracting flap reduces drag, but it also raises the stall speed because the wing loses the flap’s lift augmentation. At 58 KIAS the aircraft was already at 1.17 $V_{S0}$; a full retraction could put the new stall speed at or above the current airspeed. Use a staged retraction: establish a positive rate of climb and accelerate to about 65 KIAS, retract 40° to 20°, re-trim, then retract 20° to 0° only after reaching 70 KIAS or Vy. Keep the nose attitude shallow enough that airspeed does not decay. The priority is speed and climb, not an immediate clean configuration.
3. Explain the pitch-up after power application and how to manage trim and pitch attitude during the go-around.
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Power application produces a pitch-up tendency from increased slipstream over the tail and the changed downwash and thrust line; the pilot’s +12° attitude added to that. The resulting high angle of attack caused the airspeed decay. To manage it, pitch down firmly to the go-around attitude, hold forward pressure, and use nose-down trim only to remove the steady force-not to substitute for pitch control. Trim changes should be small and followed by a control check. Establish Vy (about 76 KIAS for this class), positive climb, then retract flap in stages. If the trim force is abnormal or the aircraft still pitches up, reduce power or check for a trim runaway rather than forcing the aircraft.