The incident quickly turned tragic.

An Air Canada regional jet hit a fire truck while landing at LaGuardia on Sunday night, killing both pilots. At least nine people are hospitalized, and hundreds of flights were canceled Monday.

Investigators want to know more about the role of the air traffic controllers and whether they were distracted by an emergency with another plane just before the crash.

Transponders would have allowed air traffic controllers to see the fire truck’s location on their instruments.

Audio recorded during the incident showed that the air traffic controller ordered the truck to stop seconds before the crash.

Two pilots of an Air Canada Express jet were killed at LaGuardia Airport. How is the crash impacting JFK and Newark air traffic? Delays, closures?

The fatal collision between a passenger plane and a fire truck on the runway of New York’s LaGuardia airport last month has revived questions about the demands on US air traffic controllers and under-investment in critical safety systems.