 FACT: At the indicated time of year, the nights in London are over  10 hours long and twilight lasts about 35 minutes. A scene set at  Gatwick Airport about 2 hours before the hijacked plane arrives in  Washington takes place in darkness, which is correct if it was about  sunset at the time of hijacking. But the takeoff time from Gatwick  referred to is about 6:30 am, long after sunrise, and indeed we see  this plane flying in daylight, still before the hijacked plane  reaches Washington.