I just caught this FedEx FX1988 flight on my radar. That’s a 75 miles straight line distance, 85 miles and 1 hr 26 min driving (with early morning light traffic). Or a 19 minute flight 
This was from my antenna, it helped that Richmond airport is about 1000 ft (300 meters) higher than me:
Similar happens around London every so often too. Today for example…
London Gatwick to London Luton and also London City to London Luton.
I guess traffic between Gatwick and Luton is busier. Here, at 5:30 AM it’s usually smooth sailing.
They are likely just positioning flights - moving the aircraft so it’s ready for a passenger carrying service from a different airport. Either the way the schedules worked out required it or possibly an aircraft went unserviceable and a replacement was needed to fill the gap. There aren’t any passenger carrying flights between the London airports like that.
Yeah, or probably to do maintenance in a less busy airport.
Positioning flight between LaGuardia (KLGA) and KJFK. 22 minutes. About 10 miles apart (driving).
