Downburst

A downburst is a strong, concentrated downdraft of air that descends from a thunderstorm and produces an outward burst of damaging winds on or near the surface. Downbursts are one of the most dangerous weather phenomena for aircraft, particularly during takeoff and landing.

Downbursts are classified by size:

• Microburst: Affects an area less than 4 km (2.5 miles) in diameter. Microbursts are particularly dangerous because they can produce wind speed changes of 30-45 knots within seconds, and they are difficult to detect visually
• Macroburst: Affects an area larger than 4 km in diameter, with winds that can exceed 60 knots

When an aircraft encounters a microburst during approach, it initially experiences a headwind increase (which increases lift and airspeed), followed by a downdraft, and then a tailwind (which decreases lift and airspeed). This rapid sequence can result in a catastrophic loss of altitude. Modern airports use LLWAS (Low-Level Windshear Alert System) and TDWR (Terminal Doppler Weather Radar) to detect and warn pilots of microburst activity.