Narrative:

I was working local control position at phl on a west operation. A GLF4 checked in on a six mile final for runway 27R. I began my runway scan; checked the asde X; which was in limited mode; and issued the landing clearance to the aircraft. At approximately a 2 mile final the aircraft asked if it was clear to land again. I re-issued the landing clearance and wind and did a quick but thorough scan of the runway. The aircraft copied the clearance but sounded hesitant in the read-back. Something didn't sound ok when the pilot read it back so I started to do another scan on the asde X. Then the pilot of the aircraft said there was lights on the runway about two thirds of the way down. I had multiple vehicles on runway 27L that were about two thirds of the way down the runway. I began another thorough check of runway 27R; starting from the approach end working toward the departure end; paused to make sure the aircraft was lined up for the correct runway; then continued my scan of the runway. I did not see any lights or beacons of any trucks on the runway. As I was finishing my scan of runway 27R; I see two headlights turn south on runway 27R at taxiway tango. At the same time the aircraft says that the lights are exiting the runway and I observed the lights exiting the runway too. At this point the aircraft was on about a half mile final. I attempted to contact the vehicle by its position on the field on all of the frequencies and got no reply. I deemed the runway to be safe and the aircraft landed safely. The aircraft exited the runway to the north and proceeded to the FBO. There were several factors that were happening at the time of the incursion. Snow removal was being conducted on runway 27L and runway 35. Asde X was running in a limited mode of operation and had multiple moving targets and stationary targets all over the taxiways and active runways. The targets are created from the snowbanks that are along the runways and taxiways. The proper configuration was entered in the asde X and the closed runways were marked with the large X's. At no time did an aural alarm; or runway occupied warning come up due to us being in the limited mode. Additionally there were multiple flashing lights all over the airport due to the snow removal being conducted on adjacent taxiways and runways. Due to the angle that the vehicle was facing on the runway and the position of the tower; I could not see the vehicle on the runway. In my first scans I did not see headlights or a amber beacon on the runway. Only when the vehicle turned south on taxiway tango did I see the headlights of the vehicle that was on runway 27R.

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Original NASA ASRS Text

Title: PHL Local Controller described a runway incursion event during snow removal operations when traffic on final questioned lights on the runway; ASDE-X provided no traffic and tower observations were restricted; vehicle was then observed exiting subject runway.

Narrative: I was working Local Control position at PHL on a West operation. A GLF4 checked in on a six mile final for Runway 27R. I began my runway scan; checked the ASDE X; which was in limited mode; and issued the landing clearance to the aircraft. At approximately a 2 mile final the aircraft asked if it was clear to land again. I re-issued the landing clearance and wind and did a quick but thorough scan of the runway. The aircraft copied the clearance but sounded hesitant in the read-back. Something didn't sound OK when the Pilot read it back so I started to do another scan on the ASDE X. Then the Pilot of the aircraft said there was lights on the runway about two thirds of the way down. I had multiple vehicles on Runway 27L that were about two thirds of the way down the runway. I began another thorough check of Runway 27R; starting from the approach end working toward the departure end; paused to make sure the aircraft was lined up for the correct runway; then continued my scan of the runway. I did not see any lights or beacons of any trucks on the runway. As I was finishing my scan of Runway 27R; I see two headlights turn south on Runway 27R at Taxiway Tango. At the same time the aircraft says that the lights are exiting the runway and I observed the lights exiting the runway too. At this point the aircraft was on about a half mile final. I attempted to contact the vehicle by its position on the field on all of the frequencies and got no reply. I deemed the runway to be safe and the aircraft landed safely. The aircraft exited the runway to the north and proceeded to the FBO. There were several factors that were happening at the time of the incursion. Snow removal was being conducted on Runway 27L and Runway 35. ASDE X was running in a limited mode of operation and had multiple moving targets and stationary targets all over the taxiways and active runways. The targets are created from the snowbanks that are along the runways and taxiways. The proper configuration was entered in the ASDE X and the closed runways were marked with the large X's. At no time did an aural alarm; or runway occupied warning come up due to us being in the limited mode. Additionally there were multiple flashing lights all over the airport due to the snow removal being conducted on adjacent taxiways and runways. Due to the angle that the vehicle was facing on the runway and the position of the tower; I could not see the vehicle on the runway. In my first scans I did not see headlights or a amber beacon on the runway. Only when the vehicle turned south on Taxiway Tango did I see the headlights of the vehicle that was on Runway 27R.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.