United flight 2384, scheduled to fly to Chicago-O'Hare International Airport, is cleared for takeoff at LaGuardia Airport by the ground controller.

United 2384 aborts takeoff due to a warning light.

United 2384 says they are heading back to the gate, noting there's an odor in the cabin that has sickened flight attendants. The pilots request a firetruck.

United 2384 declares an emergency.

Air Canada flight 8646, operated by Jazz Aviation, is cleared to land on runway 4.

An Aircraft Rescue and Firefighting (ARFF) truck, referred to as Truck 1, is heading toward United 2384 and requests permission to cross runway 4 on taxiway D.

Tower controller grants the firetruck permission to cross. “Truck one and company, cross 4 at Delta,” the tower responds.

United 2384 cleared to taxi to gate by ground controller.

About 10 seconds later, the tower controller urgently says, “Stop, stop, stop truck one, stop. Stop, stop…. Stop truck one, stop.”

Air Canada plane touches down on runway 4.

Tower controller issues first “go around,” which tells landing planes to abort landings.

Air Canada Express plane collides with firetruck. Preliminary data shows the plane's speed was around 104 mph at the time of impact with the truck, according to Flightradar24.

The pilot and co-pilot of Air Canada flight 8646 were killed in the collision, a law enforcement official said.

The National Transportation Safety Board launches a team to investigate the Air Canada collision that left both pilots dead and dozens injured.