GE Aerospace, whose joint venture made the engines of the Boeing airplane that crashed in the deadliest aviation disaster on South Korean soil, joined the investigation as Seoul extended by a week special inspections of all 101 Boeing 737-800 jets.

The flight, operated by Jeju Air, was landing when it went off the runway in Muan, in the country’s southwest. Only two people survived the crash.

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.