Icing, storms & wind shear

Thunderstorms are more than heavy rain

Moisture, instability, and lift support thunderstorms. The developing cumulus stage is dominated by updrafts; the mature stage has precipitation and both updrafts and downdrafts; the dissipating stage is dominated by downdrafts. Dissipating does not mean safe. An anvil is not a reliable sign that the storm is ending.

Hazards include turbulence, hail, lightning, icing, and outflow wind shear. Embedded storms can hide inside other clouds. Do not use gaps in a datalink radar image to thread cells. FAA guidance calls for at least 20 miles of separation from severe thunderstorms or intense radar echoes, especially under an anvil; other storms also require avoidance and that distance is not a universal safe boundary.

The wing shape is part of the performance calculation

Supercooled liquid droplets can freeze on an airframe. Rime is often rough and opaque; clear ice can spread before freezing; mixed ice combines features. Any type can seriously degrade performance. Appearance alone does not rank the danger.

Look for the overlap of moisture, temperature, altitude, and exposure. A freezing level alone is not an icing forecast. Ice changes the airfoil, adds drag, and can increase stall speed. A forecast cloud top above your climb capability is not an escape route.

For an airplane not approved for flight into known icing, plan to avoid icing conditions and follow its actual limitations. If ice is encountered, act promptly under the AFM/POH, tell ATC, and seek an exit. A descent must remain clear of terrain and be operationally available; declare an emergency when necessary.

The air changes faster than the airplane can respond

Wind shear is a change in wind speed or direction over distance. Near the ground, there is little height to absorb a loss of performance. A sudden decrease in headwind can initially reduce airspeed because the airplane’s groundspeed cannot change instantly.

Microbursts combine a downdraft with outward-spreading winds. Fronts, terrain, and inversions can also create shear. Review airport alerts, PIREPs, and TAF wind-shear groups. A WS group describes winds at a height; it is not a prediction of a specific airspeed loss.

Delay or choose another airport when conditions demand it. Know the aircraft’s approved escape procedure before takeoff or approach.

FLIGHT SCENARIO

What would change your plan?

Continue studying

Connect this lesson with related concepts:

• Weather reports and hazard advisories

Test your understanding with 9 related ACS questions.