NTSB chief: 2016 evacuation at O'Hare was 'too close for comfort'

The agency also chastised passengers for taking luggage on the chutes.

But the left over-wing slide never should have been used while the engine was running, NTSB officials said.

However, the pilots were working off a checklist that failed to differentiate between an engine fire in the air, which would requires that the remaining engine stay powered on, and one on the ground. They failed to immediately shut down the unaffected engine, the NTSB found.

Because the flight attendants did not understand how to use aircraft's phones, they were not able to communicate with the cockpit, and failed to realize that the engine was still running.

American said it was proud of the "judgement, skill, and self-discipline" of the crew, which likely prevented further injury. The airline says it welcomed the opportunity to identify emergency procedures that could have been improved.

The evacuation was further complicated by passenger's disregard for crew member instructions, according to the NTSB, which noted that many passengers slid down the chutes with their carry-on luggage.

"Things can be replaced. People can’t,” Sumwalt said Tuesday. “We know from many investigations of emergency evacuations that every second counts, and passengers need to follow the instructions of the crew members who are trying to get them out of harm’s way.”

According to the NTSB, the fire was the result of an uncontained engine failure prompted by microscopic cracks in the jet's turbine disc, which cracked and sent metal fragments spewing through the fuel tank.

ABC News' Daniel Steinberger contributed to this report.