'Black boxes' of crashed South Korean airliner stopped recording about four minutes before disaster, officials say

The critical components of the passenger plane that crashed in South Korea last month, killing more than 170 people, stopped working minutes before the plane landed and exploded on the runway, investigators said Saturday.

Officials investigating the worst plane crash in nearly three decades were hoping that information from the so-called black boxes would clarify why Jeju Air Flight 7C 2216 from Bangkok landed at Muan International Airport on December 29, burst into flames.

The disaster killed 179 passengers and crew. Two people survived.

But South Korea's Ministry of Transport said on Saturday that the cockpit voice recorder (CVR) and flight data recorder (FDR) from the Boeing 737-800 had stopped working about four minutes before the crash.

In a statement, the Ministry said it is not clear why the equipment stopped recording, adding that it will work to find the cause.

“CVR and FDR data are important data for accident investigation, but accident investigation is done through investigation and analysis of various data, so we plan to do our best to identify the cause of the accident,” said the department.

The cockpit voice recorder was first analyzed locally and then sent to the United States for testing, the department said.

The plane's data recorder, which was damaged and missing a connector, was sent to the National Transportation Safety Board in the US last week for analysis, after South Korean authorities concluded they could not extract data from the device, due to the damage.

CNN has contacted the NTSB for comment.

The accident was the worst in the country since 1997, when a Korean Air Lines Boeing 747 crashed in the jungle of Guam, killing 228 people.

It is not yet clear what the cause is, as the investigation is expected to take months.

Videos of the crash show that the rear and front landing gear were not visible at the time of the crash.

Before the emergency landing, the pilot called and used the words “bird chirping” and “go away,” according to officials, who also said the control tower had alerted the pilot to the area.

Another source of controversy was the concrete fence that the plane crashed into as it landed. Most airports do not have similar structures along the runways, according to aviation experts.

South Korean police last week also raided Jeju Air's office in Seoul and Muan International Airport employees as part of their investigation, Reuters reported.

For more CNN news and newsletters create an account at CNN.com