New Jersey ? An air traffic controller should have warned the pilot of a small plane about aircraft in its path before it collided with a sightseeing helicopter over New York’s Hudson River in a crash that claimed nine lives, federal officials said Thursday in making safety recommendations.

The National Transportation Safety Board recommended that helicopters and small planes be separated in the busy air corridor where the collision occurred, a low-altitude pathway used by about 200 helicopters and small planes daily. The call for fast-moving planes to operate at a higher altitude than helicopters is one of five safety recommendations the NTSB issued Thursday in a letter to the Federal Aviation Administration.

A second recommendation called on the FAA to emphasize the need for air traffic controllers to remain attentive, a clear rebuke to the controller responsible for the single-engine Piper that hit the helicopter Aug. 8. Questionable behavior during the incident led to the suspension of the controller and his supervisor at Teterboro Airport in northern New Jersey, where the plane originated.