I have no aviation knowledge/experience but I observed something on a flight tracking app I was curious about:
Early morning (7 AM) I watched two small planes (one of them was a piper archer) traveling close together (visually: they stayed a few streets apart) around 100 kts at an altitude of 1200 feet with both planes staying at minimum 300 feet apart in altitude. They traveled together for about 30 minutes while one plane landed and the second one flew to another airport. The second plane eventually landed at the airport but almost immediately took off after coming to a stop (say 20 seconds of time on the ground). It did a loop around the airport and then landed and didn't take off again.
My question is: what explains the behavior of the two planes? Was this some sort of training exercise? I've never seen two small planes travel so closely for so long so I'm curious.