The pilot of a plane which crashed at San Francisco airport, killing two people, may have been temporarily blinded by a bright light as he came into land.
Lee Kang Kuk, who was making his first landing at the airport and had just 43 hours' experience at the controls of the Boeing 777, said he saw a bright flash as he approached the runway.
It happened around 35 seconds before impact when Asiana Airlines flight 214 was around 500ft (150m) off the ground - the point at which the aircraft began to slow down and drop steeply.
Deborah Hersman, who chairs the National Transportation Safety Board (NTSB), said the use of lasers had not been ruled out.
It is not clear whether the flash of light caused the crash or whether other factors were to blame.
The pilot's claim came as phone calls to the emergency services made by passengers on board the plane were released, demonstrating the confusion caused when the Boeing 777 hit the runway.
Pleading for ambulances to be sent, one woman can be heard saying: "There are a lot of people that need help ... We have people over here who weren't found and they're burned really badly."
Meanwhile, it has emerged that passengers were initially told not to evacuate the aircraft.
The plane hit a sea wall as it came into land, causing its tail fin to break off and the rest of the fuselage to spin across the runway.
However, the NTSB found people did not begin leaving the plane until a fire erupted 90 seconds after impact.
"We don't know what the pilots were thinking, though I can tell you in previous accidents there have been crews that don't evacuate, they wait for other vehicles to come to be able to get the passengers out safely," Ms Hersman said.
She suggested that the pilots in the cockpit may not have been in a position to spot the fire outside the plane.
At least one of the emergency escape slides opened inside the aircraft, pinning down two flight attendants.
Three other crew members were flung from the aircraft onto the runway but survived.
The NTSB is using pilot interviews, cockpit recordings and control tower communications to piece together the moments leading up to the crash.
They found both Mr Lee and his co-pilot, Lee Jung Min, who was on his first flight as an instructor , both thought the aircraft's speed was being controlled by an autothrottle, which was set to 157mph.
When they realised the plane was approaching the waterfront runway too low and too slow, they both reached for the throttle.
Passengers heard a loud roar as the pilots made a desperate attempt to abort the landing.
Two Chinese students were killed in the crash, which left 180 people injured. The students, who began their journey to the US in Shanghai, were on their way to a 15 day camp to study English.
Families of around 20 survivors who remain in hospital have begun arriving to care for their loved ones.
Flight 214 was a direct flight from Incheon in South Korea to San Francisco.