The pilot landing a passenger jet which crashed in San Francisco tried to correct course when he saw it was off centre and too low as it approached the runway, investigators have said.

The Asiana Airlines Boeing 777 was so low that its tail section hit a seawall before the plane crashed on the runway on Saturday. Two people died and more than 180 were injured.

National Transport Safety Board chairwoman Deborah Hersman said on Wednesday that the pilot realised that the plane was too low and on an incorrect flight path when it was only 150 metres from the ground.

How it happened

82 seconds before impact: Altitude is about 1,600 feet (488 metres). Autopilot disengaged. 

73 secs: Speed 170 knots. Altitude 1,400 feet.

54 secs: Speed 149 knots, altitude 1,000 feet.

34 secs: Speed 134 knots, below safe landing target of 137 knots. Altitude 500 feet. Instructor pilot realises plane is too low.

16 secs: Speed 118 knots, altitude 200 feet. Pilots notice plane not centred to runway.

8 secs: Speed 112 knots, altitude 125 feet. Plane's throttles start moving forward. 

7 secs: Crew member calls for more speed. 

4 secs: Stall warning heard in cockpit.

3 secs: Speed 103 knots. 

1.5 secs: Call is made to abort landing.

Impact: Speed 106 knots. Tail section hits seawall and breaks off.

"They had a lateral deviation and they were low. They were trying to correct at that point," she said.

Hersman, said two flight attendants fell from the tail-less plane as it crashed.

It was not clear if the auto-throttle, which the South Korean airline's pilots said they were counting on to maintain speed, was engaged when the plane slowed to a near-stall just before it hit the seawall in front of the runway, Hersman added.

Three of the four pilots on board were in the cabin during the landing, although only two could see the runway, Hersman said.

Information from the plane's flight data recorder shows the plane was travelling far too slowly as it came in for landing.

The pilot at the controls - named by Asiana as Lee Kang-Kook - was about halfway through his training for the 777, but had led 29 flights to San Francisco on 747s in the past, according to the airline.

His co-pilot was acting as his trainer on the flight. His trainer told US investigators he had a total of 13,000 flying hours, 3,000 of which were in the Boeing 777 but he had not flown as a trainer pilot before.

"He reported that this was his first trip as an instructor pilot," Hersman said.

"This was the first time that he and the flying pilot that he was instructing had flown together."

The world's largest pilots union rebuked the NTSB for its handling of the crash investigation, saying the agency had released too much information too quickly, which could lead to wrong conclusions and compromise safety.

Releasing data from the flight's black boxes without full investigative information for context "has fueled rampant speculation" about the cause of the crash, the Air Line Pilots Association International said in a statement.

Hersman rejected the criticism. "We work for the travelling public," she said. "We feel it is important to show our work."

She said on Sunday the plane was "significantly below" its intended air speed and its crew tried to abort the landing less than two seconds before it hit the seawall in front of the runway.

Source: Agencies