Air crash investigators have said it could take years to determine the exact cause why an Asiana Airlines flight crash-landed San Francisco's airport Saturday. Deborah Hersman, head the USA's National Transportation Safety Board, said it was too early to say whether or not the accident was the result pilot error. Many analysts have already concluded that it was very unlikely that mechanical error was involved, citing the excellent safety record the Boeing 777 aircraft. Kevin Hiatt, CEO the Flight Safety Foundation, told reporters that any conclusions about what caused the crash are months, if not years, away. What is known is that the plane was flying too slowly as it approached the runway. As firefighters extinguished the last the flames the burning wreckage, survivors described the horror escaping the aircraft. They said it was a miracle that 305 of the 307 people board made it alive. Two Chinese students died the accident. Passengers were quick to praise the professionalism, quick thinking and selflessness the flight attendants, one of whom hauled an injured passenger to safety. Frequent Asiana flyer Eugene Rah recounted the heroism flight attendant Jiyeon Kim, saying: "She was a hero. This tiny, little girl was carrying people piggyback, running everywhere, tears running her face. She was crying, but she was still so calm and helping people."