Image copyright AP

The crew of the Asiana flight that crashed in San Francisco "over-relied on automated systems" the head of the US transport safety agency has said.

Chris Hart, acting chairman of the National Transportation Safety Board (NTSB), said such systems were allowing serious errors to occur.

The NTSB said the 6 July 2013 crash, which killed three, was caused by pilot mismanagement of the plane's descent.

It was the only fatal passenger airline accident in the US in five years.

The aircraft hit a seawall as it approached the airport runway, ripping off the tail and sending the body of the airplane skidding down the runaway, which then caught fire.

Media playback is unsupported on your device Media caption New footage has come to light that shows emergency vehicles at the scene of the Asiana plane crash in San Francisco in July 2013

Three people died in the crash - including one Chinese teenager who was run over by a firefighting vehicle in the chaos.

During the meeting on Tuesday, Mr Hart said the Asiana crew did not fully understand the automated systems on the Boeing 777, but the issues they encountered were not unique.

"In their efforts to compensate for the unreliability of human performance, the designers of automated control systems have unwittingly created opportunities for new error types that can be even more serious than those they were seeking to avoid," Mr Hart said.

The South Korea-based airline said those flying the plane reasonably believed the automatic throttle would keep the plane flying fast enough to land safely.

But that feature was shut off after a pilot idled it to correct an unexplained climb earlier in the landing.

The airline argued the automated system should have been designed so that the auto throttle would maintain the proper speed after the pilot put it in "hold mode".

Image copyright Getty Images Image caption NTSB board members voted on the probable cause of the crash after a nearly-year long investigation

Boeing has been warned about this feature by US and European airline regulators.

"Asiana has a point, but this is not the first time it has happened," John Cox, an aviation safety consultant, told the Associated Press news agency.

"Any of these highly automated airplanes have these conditions that require special training and pilot awareness. ... This is something that has been known for many years."

Among the recommendations the NTSB made in its report: