The National Transportation Safety Board says that the air traffic controller on duty at Teterboro Airport during the crash between a small plane and sightseeing helicopter had a "light" workload and "nothing should have prevented him" from alerting the small plane's pilot about aircraft in his route. The crash, which killed nine people, occurred as the controller were on the telephone, joking about a dead cat. Additionally, the NTSB has made suggestions for air safety over the Hudson River, "including having helicopters and planes fly at separate altitudes" and that "pilots who are to fly in the Hudson River air corridor and around the Statue of Liberty complete a special training course."