Pilots have become dependent on aircraft automation to the detriment of their manual skills, according to testimony at a National Transportation Safety Board hearing on the Asiana Airlines crash in July that killed three people and injured more than 150.

"What's clear from the study-data, we do have an issue in aviation with respect to automation and performance when it comes to interaction with human and computer," NTSB chairwoman Deborah Hersman said at today's hearing.

She added at a news conference, "clearly automation is a huge issue for the aviation community."

Watch New Footage of Asiana Flight 214 Tumble Down Runway

The NTSB, which today released video of the incident at San Francisco International Airport, said the fatal daylight crash of the Boeing 777 amid clear skies could have been prevented. The agency has yet to determine a cause.

Questioning at today's hearing focused on why none of the three pilots in the cockpit knew enough about hands on manual flight to simply throttle up before it was too late and instead let the jumbo jet lose so much air speed it hit the seawall short of the concrete landing strip.

The approach to San Francisco airport has special challenges: over water and at a steep rate of descent.

An Asiana pilot in training, who was at the pilot controls on the day of the fatal crash, told investigators after the crash "it was very stressful, very difficult to perform a visual approach with a heavy airplane."

When asked whether he was concerned about making a non-instrument, visual approach, the junior pilot answered, "very concerned, yeah."

NTSB chairwoman Hersman said at the hearing that "we we owe many of the advances in aviation safety to advances in cockpit automation. However, automation must be well understood, and monitored effectively by flight crews."

Cockpit communications released today show the Seoul to San Francisco flight approaching normally.

The 44-year-old pilot asked, "Is that the Golden Gate [bridge]," and acknowledged "runway in sight."

The "target speed for landing is 137 knots," he said, but at just 30 feet above the bay an audible warning is heard because the plane is 33 knots slow and the captain orders the junior pilot to "go around," attempting to abort the landing. But it was too late.

"The Asiana accident is a huge watershed and a big wake-up call," ABC News aviation analyst John Nance said. "We've got to stop over-relying in automation. Pilots must not be allowed to be pilots unless they really know how to fly the airplane."

Experts call it "automation addiction," which officials said figured into the Air France crash two years ago that killed 228 passengers.

In the Asiana flight, one simple move demonstrated to ABC News by a Midwest flight school could have prevented the crash: pushing the throttle forward, akin to stepping on the gas.

"We didn't have pilots in that cockpit, we had system operators," Nance said.

And unlike many of the older generation of pilots, today's aviators have little military training, which includes hundreds of hours of actually flying planes.

"Two high time, experienced pilots in the cockpit; what can be learned from this event," NTSB chairwoman Hersman said, adding that the agency has "no specific defined plans to make recommendations" after today's hearing.