The head of the Federal Aviation Administration has told Congress that the agency must do more to ensure flying remains safe after a midair collision over Washington, D.

During the hearing, the head of the National Transportation Safety Board and members of Congress again questioned how the FAA hadn’t noticed an alarming number of close calls near Ronald Reagan National Airport and addressed the problem before the January collision between an Army helicopter and a jetliner.

FAA and NTSB officials testified in front of a Senate hearing on Thursday. Today it feels like the whole world has been explored, but there are still a handful of places around the world that are off-limits to humans.