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 NTSB’s preliminary report on the Jan. 29 crash that killed 67 people current helicopter routes allowed around the airport are an ‘intolerable risk to aviation safety.’

Citing “intolerable risk for aviation safety,” the National Transportation Safety Board says helicopters should be banned from flying a certain route near Washington if two specific runways are in use.