Twelve family members of the two Chinese students who were killed and two others who were injured in Saturday's Asiana Airlines crash arrived in San Francisco at 11 pm on Monday local time.

"I just want to have one more look at my daughter," said the father of Wang Linjia, the 17-year-old Chinese victim, at Shanghai Pudong International Airport before his departure.

The eyes of Wang's parents were red and swollen. "I hope you can understand how we feel at the moment," her father said.

Investigators continued to interview the four-man cockpit crew of the crashed Boeing 777.

Deborah Hersman, the head of the National Transportation Safety Board, said the cockpit crew were being questioned as it had emerged that the plane had been flying well below the recommended speed for landing when it crashed at San Francisco International Airport, AFP reported.

"We will determine exactly what happened, when it happened and how it happened, if it was consistent with their process or procedures or if there is any deviation," Hersman said.

Flight data showed the plane was traveling at approximately 106 knots at impact - significantly less than the speed necessary for landing.

"137 knots is the speed that they want to have when they cross the threshold of the runway. The crew is responsible to make a safe approach to the airport," she said, adding that air traffic controllers "are not responsible for speed management on the aircraft".

The trainer assigned to guide the pilot at the controls when the aircraft crashed was on his first day on the job, Asiana said on Tuesday.

The carrier confirmed the pilot, Lee Kang-kook, 46, was being trained to operate the Boeing 777. The pilot assigned to guide him, Lee Jung-min, was on his first day as a trainer, Asiana later added.

The airline said Lee Kang-kook had just 43 hours experience in that model of aircraft, although he had accumulated more than 9,000 hours of flight time in other planes.

Lee Jung-min, the trainer, had more than 3,000 hours of flight time in the Boeing 777, a spokeswoman for the airline said.

South Korean President Park Geun-hye expressed her condolences to the passengers and their families on Sunday, Xinhua News Agency reported.

US President Barack Obama said his thoughts and prayers go out to the families who lost a loved one and all those affected by the crash, according to the White House website.

Asiana Airlines President Yoon Young-doo met the families of the victims at the transit boarding gate of Incheon International Airport while the Chinese group was transferring to the US through Seoul on Monday night.

"I am very sorry. I am very sorry," said Yoon, bowing to the Chinese parents, China Radio International reported.

"We will thoroughly investigate the cause of the accident, and provide details and answers to the victims' families, and determine solutions as soon as possible," Yoon said.

The South Korean airline will likely pay hundreds of millions of dollars to passengers involved in the crash, a US expert said.