TOKYO » A Japan Airlines Boeing 777 bound for San Francisco returned to Tokyo early Tuesday (Monday afternoon in Hawaii) after a warning flashed in the cockpit saying the jet’s hydraulic fluid level was low.

The plane carrying 236 passengers and 13 crew had departed around midnight and returned about four hours later to Tokyo’s Haneda airport.

Passengers boarded another plane that departed for San Francisco and arrived there safely early Tuesday local time, a company spokesman said.

Mechanics found a leak in the hydraulic system of the plane that returned to Tokyo.

The incident happened after an Asiana Airlines Boeing 777 crash-landed Saturday in San Francisco, killing two.

The National Transportation Safety Board, which is investigating the Asiana accident, has yet to reach a conclusion about its probable cause. While the focus of thr investigation could still shift, information released by the board so far appears to point to pilot error.