Washington ( CNN ) -- A US Airways Express flight crew reported seeing what looked like a flare with a smoke trail in the vicinity of their aircraft while on approach to Philadelphia International Airport on Tuesday . According to authorities , what the crew witnessed remains a mystery . The aircraft with 34 passengers and three crew members landed safely . Flight 4321 , originating from Elmira-Corning Regional Airport , was about 500 feet above the ground in Philadelphia when the incident took place . An audio recording of the communication provided by Live ATC.net between the air traffic controller and arriving planes indicated the initial confusion : . Pilot : `` It looks like a flare that was shot out . '' Tower : `` Previous arrival said something about a flare being shot up . ... You said there was a flare being shot at you ? '' Pilot : `` Yeah it was n't probably more than 50 feet off our right wing . It looked like a flare gun . '' Tower : `` OK , wow . '' The tower alerted incoming aircraft to use caution as they approached the airport . No other incidents were reported . After landing in Philadelphia , the aircraft taxied to the gate , according to US Airways spokeswoman Liz Landau . Runway 17 was closed for about 30 minutes after the incident for investigation , the FAA said . Law enforcement authorities are investigating . The aircraft involved was a Bombardier Dash 8 twin engine plane operated for US Airways by Piedmont Airlines . CNN 's Aaron Cooper contributed to this report .
A US Airways Express crew reports seeing what looked like a flare with a smoke trail . The plane was flying from New York to Los Angeles when it made an emergency landing in San Francisco on Friday afternoon. Authorities say the sighting remains a mystery .