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.

South Korean officials are struggling to determine what caused a deadly plane crash that killed nearly 180 people on board, with the nation saddened, shocked and ashamed over the country’s worst aviation disaster in decades.