The call came on a December morning while Lee Jun-hwa, an architect from Seoul, was overseas on a business trip.

“I think Mom is dead,” his younger brother told him.

A plane returning from Thailand had crashed at an airport in Muan, in southwest Korea, and their mother’s name was on a list of passengers.

Mr. Lee watched footage of the explosion, again and again, unable to accept that these were his mother’s last moments.

Weeks later, he attended a Buddhist funeral rite at the airport and was startled to see concrete slabs that peeked out from a mound of dirt at the end of the runway.

The slabs formed part of a structure housing crucial navigation antennas that help pilots find the runway when visibility is low. International safety guidelines say such structures should be made of material that breaks apart easily if a plane collides with them.