Delta to take up London Heathrow slots for Boston and Miami. Pretty aggressive route development

The grant of anti-trust immunity across the Atlantic for the oneworld group,stipulated that the alliance must surrender slots from Heathrow to both Boston and Miami. At the time there was speculation about who might claim these slots and commence operations. The answer is now known: Delta, using them to improve service to Boston and Miami. This move bears the stamp of a large, confident carrier. But is is good strategy?