Federal investigators looking for the cause of the January collision between a passenger jet and an Army helicopter near Washington, D.C., that killed 67 people are recommending a ban on some helicopter flights.

Current airport flight safety practices create an "intolerable safety risk" that could be eliminated by changing allowed separation distances between helicopters and airplanes, federal officials say.

The National Transportation Safety Board said the separation between helicopters and jets in the area was insufficient and increased “chances of a midair collision.”