Why London's Heathrow Airport Sometimes Hosts 'Ghost Flights' With No One on Them

An anonymous reader writes: Six times per week, an empty plane used to fly from London's Heathrow Airport to Cardiff, Wales. The next day, the plane would make the return trip without a single passenger. Half As Interesting, the second channel from Planelopnik-approved Wendover Productions, details why ghost flights like this sometimes operate from Britain's biggest airport in his new video. Despite being one of the most crowded airports in the world, Heathrow operates with only two runways. As a result, it's extremely difficult to get a "slot pair" -- rights for airlines to land and take off at a certain time. Only 650 slot pairs exist per day, so airlines are prepared to drop massive cash in order to get prime slot pairs. And they can trade and sell them, too. [...] Should an airline fail to use their slot at least 80 percent of the time, Heathrow will reassign it to the next company on the waiting list.