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.

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

Helicopter traffic should be permanently banned near Ronald Reagan Washington National Airport during certain periods to alleviate congestion and avoid a repeat of the deadly midair collision that occurred there in January,