Microburst Wind Shear on Final Approach

Microburst

Downdraft intensity 10.0 m/s

Outflow core radius 650 m

Approach

Target approach speed V_ref 72 kn

Flight Data

F-FACTOR: 0.00 — CLEAR

Airspeed

72 kn

Vertical wind

0 ft/min

Path deviation

0 ft

Radalt

0 ft

How it works

A microburst is a strong, localized downdraft that spreads into a horizontal outflow as it nears the ground. An aircraft flying through one meets three phases in seconds: an increasing headwind (airspeed rises, aircraft tends to balloon above the glidepath — the classic pilot mistake is to reduce power), then a downdraft pushing the aircraft down directly, then the outflow reverses into a tailwind as the aircraft exits — airspeed collapses right when altitude is lowest and there is no room left to recover.

This sim uses an idealized, continuity-consistent stagnation-flow model for the wind field (r = horizontal distance from the microburst center, y = height, R = core radius, H = outflow depth):

Downdraft:   w(r,y) = -W_max · exp(-(r/R)²) · sin(π·y/H)
Outflow:     U(r,y) = U_max · (r/R) · exp(0.5(1-(r/R)²)) · exp(-y/H)

The hazard is quantified by the real F-factor used in FAA/NASA windshear research and airborne windshear-alerting systems (Bowles, 1990) — it folds the horizontal-shear deceleration and the vertical wind into one number the flight-path energy actually "feels":

F = (1/g)·(dV_h/dt) − w/V

V_h = wind component along the flight path (+ = tailwind)
w   = vertical wind (+ = up, so a downdraft is negative)
V   = airspeed, g = 9.81 m/s²

F < 0.05 — negligible shear.
0.05 ≤ F < 0.10 — caution; performance-decreasing shear.
F ≥ 0.10 sustained — the FAA/ICAO threshold for hazardous windshear: sustained excess drag/loss of climb performance an engine at full thrust may not overcome.

Autothrottle tries to hold V_ref by adjusting ground speed with a realistic thrust-limited response — toggle it off to see why a slow, un-augmented pilot correction is far more dangerous than an alert crew reacting to an F-factor warning immediately on encounter.

Ready — press "Fly approach"

Outflow (horizontal) Downdraft core

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