BURBANK (CBS) — A Southwest Airlines flight headed for Burbank was turned back on Tuesday morning after reports of a strange odor in the cockpit.

Flight 508 returned to Oakland International Airport shortly after 7:30 a.m. after a flight attendant smelled heavy fumes toward the rear of the plane’s cabin.

One person was removed from the plane and transported to the hospital.

Southwest officials said the fumes were no longer detectable when emergency crews boarded the plane.

“At this point, the whole realm of possibility is out there,” Southwest spokesman Brad Hawkins told KNX 1070 NEWSRADIO. “We have 3,400 flights a day, so our main concern is that everyone got back on the ground safely.”

The flight’s 137 passengers were put on another plane and are now headed for Burbank while mechanics conduct an inspection.