Why 9 planes had to declare an emergency above one of Europe's busiest airports

A British Airways Airbus A320 stopped on the runway at London Gatwick Airport. Nicolas Economou/NurPhoto via Getty Images Nine airplanes declared emergencies while flying near London around midnight. London Gatwick Airport's runway was temporarily closed due to a problem with a British Airways jet. 14 flights were diverted, including one where passengers were left on board for two hours. Nine airplanes flying over London declared emergencies early Wednesday morning after an incident at one of…