Wake Turbulence on Short Final

Each wingtip generates a vortex. Viewed from behind, the left wing's vortex rotates clockwise and the right wing's anticlockwise, with descending air between them and upwash outside. Both sink at roughly 100–150 ft/min when generated by a heavy aircraft in stable air, and both are advected by the wind.

With the wind 200°/15 kt and runway 27, the crosswind component is 15 × sin70° ≈ 14 kt from the left and the headwind is 15 × cos70° ≈ 5 kt. In 90 s the vortices are carried about 14 kt × 90 s ≈ 650 m, or 0.35 NM, to the right, and sink about 190 ft.

The downwind (right-hand) vortex drifts further right and away from the approach path. The upwind (left-hand) vortex is carried towards the runway centreline and can end up sitting on or very near the approach path - which is exactly what a crosswind does to wake: it holds one vortex over the approach while pushing the other clear. So the threat is the upwind vortex, and the standard assumption that the wake is behind and below you on the centreline is wrong on this day.

Note also that a 3.5 NM gap at 140 kt is inside the usual 3-minute separation behind a heavy, so both the spacing and the wind were against you.

1. Stop the roll with prompt but coordinated aileron and rudder. A vortex-induced roll can exceed available aileron authority in the landing configuration, so it may be necessary to let the aircraft roll through part of the cycle and arrest it on the far side rather than fight it.
2. Do not pull. At VREF + 5 kt the aircraft stalls at about 1.8 g; a firm recovery pull at 500 ft can reach that in a second, converting a wake encounter into an accelerated stall at low altitude. Hold the attitude and let the aircraft fly out of the vortex.
3. Apply go-around power and establish a positive climb. With 500 ft and 3 NM to run, continuing a destabilised approach into the same air is not an option.
4. Fly above the heavy's flight path and touch down beyond its touchdown point. Vortices sink below the generating aircraft's glide path, so the safe zone is above and upwind of it, not below.
5. Advise ATC of the encounter and the go-around so the spacing behind you is protected.

The speed was still VREF + 5 kt and the shaker did not fire, which confirms the upset was external - a roll and sink at constant speed in smooth aircraft response is wake, not a stall.

Vortex strength is set by the circulation, which for an elliptic loading is Γ = 4W/(ρ V π b). So strength:

• rises linearly with weight: the heavy is several times your 60 t, so its vortex is several times stronger;
• falls with speed and span: a slow, clean, heavy aircraft is the worst generator, and at 145 kt the heavy was flying at almost exactly your 140 kt, so you were following the wake in the same air at the same speed rather than outrunning it;
• decays with time and with ambient turbulence. In light to moderate turbulence the decay is faster than in stable air, but 90 s is short and the sink had only taken the cores about 190 ft below the generation altitude - still inside your flight path.

The 90 s gap corresponds to roughly 3.5 NM at 140 kt, which is inside the usual 3-minute / 5–6 NM minimum behind a heavy and well inside what a super-heavy would require. Published minima are a floor based on average conditions; they do not account for a crosswind that parks one vortex on the centreline. Finally, your own aircraft generates a wake too - going around does not remove the problem for the aircraft behind you.