Glaze (ice)

It is a relatively common occurrence in temperate climates in the winter when precipitation forms in warm air aloft and falls into below-freezing temperature at the surface.

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.

In February 1994, a severe ice storm caused over $1 billion in damage in the Southern United States, primarily in Mississippi, Tennessee, and Alabama.

However, during the early hours of 12 January a warm front moved across the country causing freezing rain and heavy glaze, particularly in the South and West Yorkshire areas of Northern England (crucially, this rainfall had stopped before first light).

When the local population prepared to set out for work and school, they saw from their windows what appeared to be clear roads and pavements but which were in fact treacherous sheets of black ice.

[8] Accident and emergency units at hospitals in the Sheffield, Rotherham, and Barnsley areas found themselves inundated by people with broken bones, fractures, and sprains, and many schools were closed as it was judged unsafe for pupils to attempt to make their way there.

As a result, the airport was shut down and hundreds of passengers were stranded inside, with taxi drivers charging up to 10,000 rubles (US$330) for a one-hour drive to the city.

As the plane circled, the freezing rain formed a ridge of glaze on the upper surface of its wings, eventually causing the aircraft's autopilot to suddenly disconnect and the pilots to lose control.