British Airways has signed a transatlantic tie-up with American Airlines and Iberia that, it says, is worth a combined $7bn (£4.4bn) a year.The deal allows the airlines to share passengers and costs on flights between the European Union, Switzerland and Norway and the US, Canada and Mexico.BA said the joint business would launch next month and give customers "greater access to discounted fares".A tie-up between the airlines received regulatory approval this summer.The tie-up had been vigorously opposed by rival Virgin Atlantic, which said it would create a "monster monopoly".BA has already signed a merger agreement with Spain's Iberia to form a new company called International Airlines Group.The BA and Iberia brands will, however, continue to operate as normal.Source: BBC