The black boxes from a Jeju Air Boeing 737-800 that crashed in South Korea on December 29 stopped recording four minutes before impact, complicating the investigation into the crash that killed 179 of 181 people on board.

The plane skidded off the runway in Muan after a bird strike and landing gear failure, striking a concrete localizer structure.

Officials are investigating the black box failure and have pledged to improve airport safety, as experts link the high death toll to the localizer’s construction, ABC News has reported.

The U.S. NTSB is assisting with the analysis.

Written by B.C. Begley