Nov. 10 (UPI) -- A hazmat team responded to a Frontier Airlines plane Thursday night to test for possible poisonous gas after the crew fell sick from what they described as a "strange odor" on a Denver to San Antonio flight.
Four flight attendants felt ill, but firefighters were unable to find the odor.
It occurred on the same day that another Frontier flight -- from Baltimore to Atlanta -- got a bomb threat.
"Originally, we were called for a strange odor on a plane and people feeling bad so we sent a whole lot of people -- hazmat, rescue, airport rescue, all these things out there -- but once the plane landed, we realized there was no odor," San Antonio Fire Department Public Information Officer Joe Arrington said.
He said no passengers reported feeling ill.
The Frontier flight attendants had reported "a fume-like odor" in the rear of the plane but no evidence of the odor was found by firefighters and airline maintenance workers are trying to track down a possible cause.
The bomb threat was reported by a passenger who said they received an AirDrop message claiming a bomb was onboard Frontier Flight 1571. The plane landed safely.
The FBI boarded the plane and Atlanta police dogs checked the plane and passengers, finding no evidence of explosives.
"Per standard protocol, the flight crew notified appropriate authorities and has safely landed at Hartsfield-Jackson Atlanta International Airport. Emergency personnel are on scene," Frontier Airlines said in a statement.
The FAA will investigate.