Federal investigators on Thursday detailed a series of issues and failures that led up to last month’s deadly collision between a regional jet and a fire truck at New York’s LaGuardia Airport.

According to a preliminary report from the National Transportation Safety Board, the truck drove through the airport’s version of a stop light and lacked a transponder, hampering the crash warning system. At the time, there was also heavy air traffic and an emergency involving another plane.

Air Canada Express Flight 8646, a regional jet from Montreal with 76 people aboard, collided with the fire truck seconds after landing on March 22. Pilots Antoine Forest, 30, and Mackenzie Gunther, 24, were killed, and 39 others were taken to hospitals with injuries including the two occupants of the fire truck.

This incident marked the first deadly crash at LaGuardia in 34 years. Key takeaways from the NTSB report include:

Busy Air Traffic Controllers

Only two air traffic controllers were on duty the evening of the crash, which was normal; however, the airport was busier than usual, with the number of arrivals and departures more than double what was scheduled due to flight delays. The controllers were managing the traffic along with an emergency involving a departing jet.

No Transponder on the Fire Truck

LaGuardia features an advanced surface surveillance system to track both aircraft and ground vehicles, which uses transponder data. However, the fire truck involved in the crash was not equipped with a transponder, leading to difficulties in tracking its movements.

Red Lights were On

On the night of the incident, Air Canada received clearance to land while the fire crew asked to cross the runway. Despite a system of red lights warning of crossing traffic being illuminated, the fire truck was cleared to cross by the controller.

‘Stop, Stop, Stop’ Calls

Prior to the crash, the controller warned the fire crew to stop just moments before the collision. Miscommunication and the busy nature of the control tower contributed to the tragic outcome.

Investigations are ongoing as safety experts stress the importance of adherence to safety protocols in busy airport operations.