WASHINGTON - The pilot whose Boeing 777 crashed last summer at the San Francisco airport told investigators he was "very concerned" about attempting a visual approach without the runway's instrument landing aids, which were out of service because of construction, according to an investigative report released Wednesday.

Lee Kang Kuk, a 46-year-old pilot who was landing the big jet for his first time at San Francisco, "stated it was very difficult to perform a visual approach with a heavy airplane." The jet came in too low and slow and crash-landed, killing three people and injuring more than 200, according to the National Transportation Safety Board.

A visual approach involves lining the jet up for landing by looking through the windshield and using numerous other cues, rather than relying on a radio-based system that guides aircraft to the runway.

The investigative report was released at the start of a daylong NTSB hearing that was called to answer lingering questions about the crash, not to conclude exactly what went wrong.

Though Lee was an experienced pilot with the Korea-based Asiana Airlines, he was a trainee captain in the 777, with less than 45 hours in the jet. He had not piloted an airliner into San Francisco since 2004, according to NTSB investigator Bill English.

So far, the investigation has not found any mechanical problems with the 777 prior to impact, although testing is continuing, English said.

Lee told investigators that he realized others had been landing safely at San Francisco without the glide-slope indicator, an array of antennas that transmits a signal into the cockpit to help with the descent. That system was out of service while the runway was expanded. It has since been restored.

In his interview, the trainee said that while privately he was "very concerned" about his ability to do a visual approach, "everyone else had been doing [it], so he could not say he could not do the visual approach."

Boeing's retired 777 chief pilot, John Cashman, underscored that auto controls are not designed to replace pilots.

"The pilot is the final authority for the operation of the airplane," he said.