In the aftermath of 9/11 until it was suspended in July 2005, there was a TSA Security Directive that has required all passengers flying into and out of Ronald Reagan Washington National Airport to be seated for 30 minutes after departure or before arrival.
It's possible that the airport where you were arriving has a similar rule.
Last edited by TWA884; Dec 21, 2019 at 8:01 pm
Reason: Typo in end date