The investigation into the cause of the Asiana Airlines Flight 214 crash landing at San Francisco International Airport on Saturday (San Francisco time) is making progress just one day after the accident that killed two passengers and injured about 180 others.

The U.S. National Transportation Safety Board and the Korean inspection team dispatched to the crash site revealed some of the facts of the moments just before the landing and the investigation of the pilots.

The focus of the joint investigation by the United States and Korea fell on finding what caused the tail of the aircraft to strike the seawall at the end of the runway, which led to the catastrophic crash landing.

In a press conference on Sunday (local time), the NTSB announced the preliminary results of its analysis of the “black box” from Asiana Flight 214. According to the investigator, the cockpit voice recorder showed the plane was flying significantly slower than its pilots had intended. They recognized that fact a few seconds before landing and tried to abort the landing less than two seconds before the plane crashed on the runway.

Asiana’s top management and some of the passengers confirmed that there was no in-flight announcement of a possible issue before the landing. Taking this in consideration, sources say the problem occured shortly before landing and the pilots could not control the situation in advance.

When asked if pilot error was a main factor in the crash, however, NTSB head Deborah Hersman responded that it was too early to say, adding, “We have determined what the focus of this investigation will be, but everything is on the table.”

With the announcement of NTSB’s preliminary results from the black box, finding the cause of the crash depends on questioning the pilots in order to know what happened in the cockpit of the Boeing 777 before landing.

NTSB and the Korean task force are jointly questioning Lee Kang-gook, the pilot who was sitting in the captain’s seat of Asiana Flight 214 at the time of the crash, and Lee Jeong-min, who was co-pilot, Choi Jung-ho, the head of South Korean’s Aviation Policy Bureau at the Ministry of Land, Infrastructure and Transport, said in a media briefing on Monday (Seoul time).

According to Choi, Lee is one of Asiana’s most experienced pilots, but he was somewhat new to the Boeing 777. Lee had 43 hours of experience flying the B777-200, Choi confirmed.

Despite rising questions over possible pilot error, government officials said it would take more time to know what caused the incident.

Beyond a possible pilot error or a mechanical problem, NTSB said it is also looking into whether construction at the airport may have played a role.

Construction to extend the runway safety area temporarily shut down the glide slope system, which is one of several options pilots have to help them land planes safely, the NTSB said in a press conference.

By Seo Jee-yeon  (jyseo@heraldcorp.com)