The deadliest accident in aviation history occurred in 1977, when two Boeing 747 jumbo jets collided on a foggy runway on the Spanish island of Tenerife, killing 583 of the 644 people on board the planes. Spanish investigators blamed the captain of the KLM 747 for taking off without clearance from air traffic controllers.

The spike in fatalities marks a reversal from 2023, which became the safest year ever in aviation with no deaths among large passenger jetliners.

The U.S. NTSB is leading a team that includes investigators from the Federal Aviation Administration and Boeing, the aircraft’s manufacturer.