2011-06 · NASA ASRS report 952745
SAN Controller described an ASDE-X alert when landing traffic directed to exit at Taxiway B9 awaited traffic exiting from the gate area and activated the alert; the reporter noted the ASDE-X equipment was misaligned.
I was working the Ground Control position. Aircraft X; B757 was exiting the runway and given instructions to taxi to the ramp via 'Bravo.' (the taxiway). B757 was clear of the runway and slowed because there was an aircraft in the alley and the pilot desired to proceed in a straight line to his gate. The aircraft in the alley was holding short of 'Bravo' as instructed. B757 then stopped and was instructed to taxi Westbound on 'Bravo' to the ramp. He replied that the other aircraft needed to move to allow him to his gate. The aircraft in the alley was then instructed to angle to his right and join 'Bravo'; which he did. Aircraft Y a B737 was then able to taxi straight line to his gate. Meanwhile the Local Controller had issued a takeoff clearance to Aircraft Z; another B737. The ASDE-X is not properly aligned and showed the Aircraft Y target edge touching the runway edge at the Bravo 9 Intersection. Also the B757 target display on the ASDE-X is much larger than the actual aircraft size. The ASDE-X alerted as the Aircraft Z (B737) was on departure roll. Aircraft Y was clear of the runway and was again slowly moving toward his gate at this time. If either the target size was realistic; or the map properly aligned; there would have been no alert. Recommendation; I recommend that the ASDE-X at SAN map be properly aligned. I also recommend the aircraft target size be adjusted to realistically represent the aircraft size.
I was working the Local position; Aircraft X B757 had just landed Runway 27 and was instructed to turn left at Bravo 9 to exit the runway then contact Ground Control frequency. Aircraft Z a B737 was then instructed to LUAW on Runway 27. A scan of the runway was conducted and revealed that Aircraft X another B737 had in fact exited completely off the active runway; so Aircraft Z was given the clearance for takeoff. Several seconds after Aircraft Z was already committed on departure roll; the ASDE-X set off an alert; warning that Runway 27 was occupied. In reaction; I scanned the runway again along with the ASDE-X; and could see that Aircraft X was still in the same position at Bravo 9; still clear of the runway; but hadn't taxied yet towards their gate. Although; Aircraft X was clearly off the active; the map alignment of the ASDE-X determined that the B757's larger yellow icon was too close to the runway edge and in response triggered an alert. After the ASDE-X event; it was revealed that Ground Control had instructed Aircraft X to turn onto Bravo three times; however; he would not comply due to Aircraft ZZ outbound from the alleyway in front of him. Aircraft X didn't want to turn on Bravo because he said Aircraft ZZ was in the way. Recommendation; first; I would certainly have ASDE-X inconsistent alignment with the map be addressed. Perhaps a more positive approach with the larger (B757/B767) aircraft exiting at B9; in front of an open alleyway which is occupied; would be to either ensure that Ground Control holds the alleyway traffic short of Bravo; or local exits the arriving aircraft at B10 if it is clear that traffic from the west alley has committed outbound onto taxiway Bravo. This procedure would certainly require coordination between Local and Ground Control position so each Controller can anticipate its impact on subsequent flow of their traffic and other responsibilities. In addition; if Ground Control had advised Local that Aircraft X was not complying with instructions to move because of Aircraft ZZ; keeping in mind the inconsistencies with the ASDE-X alignment; may have opened up alternative options for Local with respects to use of runway at that point in time.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.
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