The US National Transportation Safety Board is investigating the aborted landing of a plane carrying First Lady Michelle Obama earlier this week, a spokeswoman said today.

A US air traffic controller was suspended after being asleep while a medical flight was landing in Nevada.

Planes were grounded, trains stood still and Greyhound buses were not rolling in the American north-west, leaving stranded US travellers wondering when they would be able to escape the icy, grey mess created by a major snowstorm.