SFO (CBS SF) — A United Airlines flight bound for Washington, D.C., has made an emergency landing at SFO Monday morning after experiencing an unknown mechanical issue, according to airport officials.

SFO officials said United Flight 516 departed from San Francisco International Airport at 9:23 a.m. but experienced unspecified mechanical issues within 20 minutes of take off.

The plane returned to the airport and landed safely at SFO at 10:09 a.m., according to airport personnel. The plane was taxiing back to the gate on it’s own power.

So far, there is no word from airline or airport officials what the mechanical problem the plane experienced was or when the flight would resume its journey.