NEW YORK (AP) — A firefighter whose truck collided with an Air Canada jet last month on a runway at LaGuardia Airport in New York, killing both pilots, heard an air traffic controller warn “stop, stop, stop” but didn’t know who it was for, federal investigators said Thursday.

The National Transportation Safety Board (NTSB) issued a preliminary report revealing that a critical crash prevention system failed to generate necessary audio or visual alerts in the control tower. Runway entrance lights, which serve as stop indicators for crossing traffic, remained illuminated until just before the collision occurred. The failure of the system to provide adequate warnings may have contributed significantly to this tragic incident.

After the initial warning, the fire truck's turret operator recognized that the command was directed at them, but by then, the truck had already entered the runway as Air Canada Express Flight 8646 was landing.

The minutes leading up to the crash were hectic, with flight delays causing a surge in arrivals and departures, creating a more crowded environment at LaGuardia. With more than a dozen flights arriving in the 40 minutes prior to the crash, there was heightened pressure within the control tower to manage multiple aircraft and emergency responses at the same time.

Eyewitness accounts indicated that the fire truck involved was part of a convoy responding to an emergency situation on a United Airlines flight. This unfortunate accident marks the first deadly incident at LaGuardia in 34 years, as officials are now left grappling with the consequences of the lapses in communication and technology that led to this tragedy.