Washington (AFP) – Airlines cancelled several hundred US flights Saturday at the start of a long and almost certainly messy holiday travel weekend as carriers struggled to staff their planes. As of mid-day, with Americans gearing up for July 4 Independence Day celebrations, some 600 flights within, into or out of the United States had been cancelled and more than 2,500 were delayed, according to flight tracking service flightaware.com. The numbers on Friday were awful as well, with 587 US flights scrapped among a global total of 3,060 cancellations, the site said. For days, amid a surge in tra…