(Reuters) — U.S. investigators on Tuesday said Boeing Co. should consider changing flight controls on the 777 jetliner in response to an Asiana Airlines crash in San Francisco last July that killed three people and injured more than 180.

The National Transportation Safety Board accepted 30 findings following an 11-month investigation into the July 6, 2013 crash, and used them as the basis for more than two dozen recommendations to the Federal Aviation Administration, the Seoul-based airline, Boeing, firefighters and San Francisco city and county.

NTSB Investigator-in-Charge Bill English said the investigatory team did not find any failures in the auto-throttle system or any other flight control or warning system.

Staff said the pilots committed 20 or 30 errors in the final 14 miles of approach, and cited “mismanagement” by the pilots as the probable cause of the crash.

The pilots, though experienced, didn’t understand exactly how the auto throttle system functioned and that it would not maintain minimum air speed in all circumstances, even if it was turned on.

That complexity, and flight training manuals that did not clearly describe how the controls would operate, contributed to the crash, the NTSB found.

The airline’s training also may not have adequately prepared the co-pilot, who was supervising the captain making his first landing at the airport in a Boeing 777. Crew fatigue also played a role, the NTSB investigators said.

The board recommended that Boeing “develop and evaluate” changes to the control systems to ensure the plane’s “energy state” — a combination of speed, altitude, engine thrust and other factors — “remains at or above the minimum desired ... for any portion of the flight.”

The NTSB staff said the auto throttle could have better protected against low speed. In “hold” mode, the system will not “wake up” and prevent the plane’s speed from slipping below the minimum needed to keep it aloft.

An automatic low-speed protection feature is available when the auto throttle is turned off. Had it “been available at the time of the accident (while in “hold mode”) the auto throttle would likely have increased 20 seconds before impact, which may have prevented the accident,” said Roger Cox, a senior NTSB air safety investigator.

The Boeing 777, a wide-body, long-range aircraft in operation since 1995, has a vaunted safety record, with no prior fatal accidents since its introduction in 1995.

The Asiana crash, the first fatal air accident in the U.S. since 2009, spurred scrutiny of pilots for relying too heavily on automated systems to fly planes, something critics say has eroded hand-flying skills and awareness.

Boeing has said its design principle for the system, and the “hold mode,” are to allow the pilots to ultimately be in charge of the aircraft. That principle has been consistent for more than 30 years on Boeing’s 747, 757, 767, 777 and 787 models.

Boeing did not immediately respond to a request for comment.