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