The investigation into South Korea’s recent deadly plane crash has underscored a shortcoming first identified more than two decades ago — that older aircraft lack the technology to keep the cockpit voice recorder working when the main power sources fail.

The two flight recorders on board a South Korean airliner stopped working before the jet crashed during an emergency landing and subsequent crash that killed 179 of the 181 people on board, officials said Saturday.

The discovery of the missing data suggests all power may have been cut, which is rare, a former government accident investigator said.