I thought though that at high-traffic airports, such as LHR the a/c computers are programmed to arrive at a certain point and a certain time so as to get a landing spot? I've been on flights where departing we missed the departure time then had to hold for an hour before leaving for the UK.

P.S. Am I the only one who thinks it's totally awesome when the 777 is up there at 40,000 feet in the freezing night sky, going M0.82, engines running so efficiently and quiet