The pilot of a South Korean airliner that crashed in San Francisco in July felt very stressed about touching down without a functioning instrument landing system to guide him, according to documents made public Wednesday.

Three passengers died when Asiana Airlines Flight 214 clipped a seawall with its landing gear, skidded off the runway and burst into flames at the tragic end of an otherwise routine flight from Seoul on July 6.

Another 182 passengers and crew aboard the Boeing 777 were injured, in the first fatal commercial airline crash in the United States since 2009.

A summary of Captain Lee Kang-Kuk's interview with US air accident investigators was released Wednesday as part of a day-long National Transportation Safety Board (NTSB) hearing in the US capital.

"We have the opportunity today to ensure that the lessons of this tragedy are well-learned and that the circumstances are not repeated," NTSB chairwoman Deborah Hersman said.

According to the NTSB summary, Lee -- a seasoned aviator undergoing transition training to the Boeing 777 -- told investigators he felt "very stressful" about making a visual approach.

The instrument landing system (ILS) at San Francisco had been out of service since June due to construction work, calling for a hands-on approach on an otherwise fine summer day.

Under normal circumstances, the ILS would let pilots know if they were too high or too low. A visual approach requires looking out the window and taking cues from an array of approach lights at the runway's edge.

"Asked about whether he was concerned about his ability to perform a visual approach, he said, 'Very concerned, yea'," the NTSB summary said.

"Asked what aspect he was most concerned about, he said 'the unstable approach'" -- the ability to set up an airplane for landing at a precise speed, direction and rate of descent.

"He added, 'exactly controlling the descent profile and the lateral profile, that is very stressful'."

Lee had flown Airbus A320s for Asiana from 2005 until February this year, when he began training to master the bigger 777.

He had 9,700 hours of flight experience, but only 35 hours in the Boeing 777.

Earlier in his career, he told investigators, he had twice landed at San Francisco, once manually, as co-pilot of an Asiana Boeing 747.

In the co-pilot's seat at the end of the 10-1/2 hour flight was Lee Jung-Min, who had 3,200 hours' experience in the Boeing 777 but was only recently certified to instruct other pilots on its operation.

Bill English, the NTSB investigator leading the Asiana probe, said the autopilot was switched off about three miles out, and that the airspeed dipped as low as 103 knots, or 34 knots below the ideal approach speed.

The aircraft, meanwhile, descended so low that an array of approach lights at the end of the runway -- a key visual aid to landing -- showed four red lights, a situation that would call for an aborted landing.

A final NTSB report is not expected before the middle of next year.

None of the ill-starred flight's four pilots, 12 flight attendants and 291 passengers, many of them South Korean and Chinese nationals, were scheduled to testify Wednesday.

All three of the fatalities were young Chinese women, including one who was fatally hit by a fire engine as she lay stricken near the runway.

Giving expert testimony, Nadine Sarter, who studies the impact of automation on human performance, said a complex automation system was most likely to be a hindrance at the very instant it is most needed.

"In that sense, it could get in the way," said Sarter, an engineering professor at the University of Michigan.

"Pilots sometimes rely too much on automated systems and may be reluctant to intervene" when a situation calls for hands-on control, added Federal Aviation Administration (FAA) scientist Kathy Abbott.

Captain Dave McKenney of the International Federation of Air Line Pilots'  Associations (IFALPA) said today's pilots are expected to use automated systems so often that they get "few chances" to keep up their manual skills.

He underscored the challenges of landing at San Francisco, where pilots would be busy not only setting up for landing, but also looking out for other traffic to avoid a mid-air collision. (AFP)