The US National Transportation Safety Board (NTSB) confirms on 7 July that the pilots of Asiana Airlines flight 214 flew slower than the target approach speed and attempted a go-around about 1.5sec before crashing on the runway at the San Francisco airport.

The new data from the cockpit voice recorder examined overnight by the NTSB show that a flight crew member aboard the Boeing 777-200ER called to increase speed about 7sec prior to impact.

The flight data recorder also confirmed that a stall warning activated aurally and physically as the crew plunged below the 137kt target approach speed.

"The speed was significantly below 137kt," says NTSB chairman Deborah Hersman. "We're not talking about a few knots."

The transcript and data record adds to mounting evidence of pilot error in the incident that killed two passengers and injured more than 180, of the 307 passengers and crew aboard the aircraft, although the NTSB continues to rule nothing out.

Earlier in the day, Asiana Airlines reportedly acknowledged there was no evidence of mechanical error aboard the 777-200ER or the Pratt & Whitney PW4090 engines.

Hersman verified the Asiana executive's remarks. The voice recorder revealed no discussion among the crew of any systems or power anomalies as the aircraft was on final approach. In the moment before impact, the data recorder shows the engines responded normally after the crew commanded the futile go-around attempt.

The tail of the 777-200ER slammed into the seawall separating the San Francisco Bay from the foot of Runway 28L. The aircraft also damaged several of the precision approach path indicator (PAPI) lights that precede the runway.

If they were functioning before they were damaged, the PAPI lights should have indicated to the flight crew if their approach was too low.

Flight 214 was flying a normally routine visual approach on Runway 28L, with a 7kt wind from the southwest and 10mi visibility. All that is required for such an approach is the visual recognition of the runway.