The National Transportation Safety Board says a firefighter whose truck collided with an Air Canada jet last month on a runway at New York’s LaGuardia Airport, killing both pilots, heard an air traffic controller warn “stop, stop, stop” but didn’t know who it was for. That's according to an investigative report released on Thursday. The NTSB said in a preliminary report on the March 22 crash that a crash prevention system for air traffic controllers didn’t generate an audio or visual alert. The report said the truck started moving while warning lights that act as a stop sign for crossing traffic were still lit.