The airport chaos that hit tens of thousands of travellers yesterday was based on a faulty ash cloud prediction.Officials closed south-eastern airspace for ten hours following a Met Office alert about dangerous levels of ‘black’ ash.Yet when the forecasters took fresh soundings, and sent up a plane to check, they found their assessment was flawed: there was no such ash. By the time the mistake had been realised, Heathrow had cancelled 169 arrivals and departures and Gatwick more than 200. An estimated 50,000 passengers were affected.Willie Walsh, boss of British Airways, said the shutdown was a gross over-reaction to...