OPS16IA009 · Cessna 172S S

Runway 22 left/right and 26 left/right were being used for arrivals and departures. The pilot of N269ME was instructed to LUAW on runway 22 left at taxiway P. The LUAW instruction was issued instead of a takeoff clearance because Delta flight 837 was on approach to runway 26 left and could have conflicted with an aircraft departing runway 22 left. The local control 1 (LC1) controller had put three aircraft in line up and wait (LUAW); two on runway 26R and one on runway 22L. Delta flight 837 (DAL837) had landed on runway 26 left and the pilot required additional taxi information to navigate from the runway to the terminal. The location of DAL837 and the taxi route were not in the local controller's traditional field of view but rather behind the controller and more than a mile from the tower cab. Shortly after providing detailed taxi instructions to DAL837, the controller instructed the pilot of Kaleo 1535 to turn inbound, land beyond the intersection of runway 22 left and 26 right and cleared the pilot to land on runway 22 left. The pilot acknowledged runway 22 left. The LC1 was then attending to other traffic issues when the Airport Surface Detection System, Model-X (ASDE-X) alarmed indicating a conflict on runway 22 left where N269ME was in LUAW at the intersection of taxiway P. Kaleo 1535 had crossed the landing threshold of runway 22 left when the LC1 issued go around instructions. Kaleo 1535 initiated a go around and overflew N269ME. The vertical separation was estimated to be within 100 feet. The LC was working the local control 1 (LC1) and local control 2 (LC2) positions combined at the LC1 position. He had three aircraft in LUAW simultaneously and was focused on runway 26 right and 22 right where the three aircraft were LUAW. Services provided to additional aircraft increased workload and created a distraction to the LC1 traffic management/planning actions. The LC1 forgot that he had an aircraft in LUAW on runway 22 left and cleared the Kaleo 1535 flight to land on runway 22 left. The location and orientation of the LC1 position in the tower created a challenge for the LC1 controller when the LC1 and LC2 positions were combined in the tower in that the controller was responsible for areas of the airport he/she could not readily observe and deconflict. The assisting controllers in the tower, the controller-in-charge and the local assistant were otherwise occupied and did not assist the LC1.

Verbatim NTSB analysis and probable cause from the NTSB dataset