A firefighter whose truck collided with an Air Canada jet on March 22 at LaGuardia Airport heard air traffic control warnings to "stop, stop, stop" but initially did not know the commands were directed at his vehicle, according to a preliminary report released Thursday by the National Transportation Safety Board.

The collision between Air Canada Express Flight 8646 and a Port Authority fire truck killed both pilots and injured about 40 people, including the two firefighters in the truck. The CRJ900 regional jet from Montreal was carrying more than 70 people when it struck the fire truck during landing on Runway 4 shortly before midnight.

Investigators found that an air traffic controller cleared the fire truck to cross the runway just 12 seconds before the aircraft touched down. The fire truck was leading a convoy of six emergency vehicles responding to reports of a strong odor in a United Airlines cabin that was making flight attendants ill. When the controller issued the initial stop warning, the truck's turret operator heard "Truck 1, stop, stop, stop" and realized the warning was meant for them, but by then the vehicle was already on the runway as the approaching aircraft was landing.

A key safety system designed to prevent runway collisions failed to generate alerts because the fire truck lacked a required transponder, the NTSB found. The Advanced Surface Detection Equipment system (ASDE-X) at LaGuardia, which is installed at 35 major U.S. airports, is designed to track all aircraft and vehicles on airport surfaces and alert controllers to potential conflicts. The proximity of multiple emergency vehicles also prevented the system from triggering an alarm.

The airport was experiencing unusually heavy traffic that night, with flight delays pushing arrivals and departures after 10 p.m. to more than double the scheduled amount. Planes were landing every few minutes, with a dozen flights arriving between 11 p.m. and the time of the crash. Runway lights that serve as stop signals for crossing traffic remained illuminated until approximately three seconds before impact.

This marked the first fatal crash at LaGuardia Airport in 34 years. The NTSB's preliminary report focuses on the sequence of events and communication failures, while the agency continues its investigation into the full causes of the accident.