SEOUL/MUAN COUNTY: The investigation into the crash of a South Korea passenger jet gathered pace on Wednesday as bereaved families began to prepare funerals after authorities finished formally identifying the 179 victims of the country's worst air disaster. The transport ministry said South Korean investigators have extracted the data from the plane's cockpit voice recorder and will convert it into an audio file, critical information to try to explain the few minutes that led up to the crash. The investigation team is still working to extract the contents of the flight data recorder, which was found missing a key connector, the ministry said. All 175 passengers and four of the six crew members were killed on Sunday when the Jeju Air 089590.KS jet belly-landed at Muan International Airport in the country's southwest and slammed into a sand-and-concrete embankment at the end of the runway, where it burst into flames. Two crew members, located near the tail of the Boeing 737-800, survived the disaster. The government has declared a national mourning period until January 4 and the country will scale back New Year's celebrations. The transport ministry said two more US officials arrived late on Tuesday to join a team of around two dozen investigators including from the US National Transportation Safety Board (NTSB), Federal Aviation Administration, and aircraft maker Boeing BA.N. "They're also planning to start a visual investigation into the wreckage," deputy minister for civil aviation Joo Jong-wan told a briefing. Officials have said investigators were expected to examine whether a bird strike, a failure of the landing gear to drop or if problems with any other control systems played a role in the disaster. They will also investigate the pilot's apparent rush to attempt a landing right after he had declared an emergency, officials have said. Air safety experts have also questioned if the airport embankment designed to prop up navigation equipment was built too close to the end of the runway. South Korea's acting President Choi Sang-mok on Wednesday called for a fair and objective investigation, and said funeral procedures have begun after all the victims were formally identified. "The most urgent matter at present is to return the victims to their families," Choi told an intra-agency meeting. Airport authorities set up an altar late on Tuesday and on Wednesday buses carried relatives of victims to the crash site so that they could pay their respects, just metres from the crashed plane's charred and broken tail - the only relatively intact part of the aircraft following the accident. The Muan airport was brimming with mourners seeking to pay their tributes at the altar, leading to a queue of several hundred metres. County officials sent an alert to urge visitors to go instead to a larger memorial set up in a sport complex about 9km (5 miles) from the crash site. It could still take several days until all bereaved relatives are able to secure the release of the bodies of their loved ones.