What to know about the safety system that failed to prevent the deadly runway collision at LaGuardia

The systems in place at LaGuardia Airport to prevent collisions failed to keep an Air Canada jet from smashing into a fire truck that had just pulled out on the runway as the plane was landing. The National Transportation Safety Board will determine what went wrong before Sunday’s crash that killed both pilots and injured dozens of others. One of the two air traffic controllers on duty that night cleared the fire truck to cross the runway just 12 seconds before the plane carrying 76 people touched down. There will almost certainly be multiple factors that contributed to the crash. Investigators are just beginning their work to identify the cause and what should be done to prevent similar tragedies.