Glaze from freezing rain is also an extreme hazard to aircraft, as it causes very rapid structural icing. Most helicopters and small airplanes lack the necessary deicing equipment to fly in freezing rain of any intensity, and heavy icing can overwhelm even the most sophisticated deicing systems on large airplanes. Icing can dramatically increase an aircraft's weight, and by changing the shape of its airfoils also reduce lift and increase drag. All three factors increase stalling speed and reduce aircraft performance, making it very difficult to climb or even maintain level altitude. Icing is most easily evaded by moving into warmer air—under most conditions, this requires aircraft to descend, which can usually be done safely and easily even with a moderate accumulation of structural ice. However, freezing rain is accompanied by a temperature inversion aloft, meaning that aircraft actually need to "climb" to move into warmer air—a potentially difficult and dangerous task with even a small amount of ice accumulation.