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.

Investigators are trying to figure out what caused a Jeju Air flight to land without its landing gear down in South Korea, killing 179 people.

The Jeju Air crash, which killed 179 people, was as rare as it was tragic. Here’s what travelers should know about air safety.