What happened
On June 26, 2023, at 15:47 UTC, a runway incursion occurred at Porto Airport (LPPR), Portugal. An Airbus A321neo, registration CS-TSI, had been authorized to line up on runway 35 and was awaiting takeoff clearance. Meanwhile, a Boeing 737-800, registration EI-DLX, was on short final approach to the same runway.
As the Boeing 737-800 approached the threshold, the pilot noticed the Airbus A321neo still occupying the runway and contacted the air traffic controller to confirm the presence of the other aircraft. Upon receiving this alert, the controller immediately instructed the Boeing 73 and-800 to perform a go-around. Data indicates the Boeing 737-800 descended to 275 feet AGL at a distance of 950 meters from the runway threshold before regaining altitude. There were no injuries and no aircraft damage resulting from the event.
The investigation
The GPIAAF investigation examined air traffic control recordings, A-SMGCS/SMR data, and witness statements. The investigation focused on the high-workload environment at the tower and the physical layout of the control position. Investigators found that the tower controller was managing intense traffic activity, including multiple aircraft requesting push-back and various ground vehicles in the movement area.
Crucially, the investigation identified that the controller's view of the runway 35 threshold was obstructed by a metal structural beam, a consequence of a 2021 tower renovation. This obstruction prevented the controller from visually detecting the CS-TSI at the threshold. The situation was only identified because a temporary supervisor, positioned with a clear line of sight, alerted the controller alongside the pilot's radio call.
Findings
- The controller experienced a loss of situational awareness due to high workload and intense ground movements.
- A structural metal beam in the tower obstructed the controller's visual monitoring of the runway 35 threshold.
- The tower's operational setup required the Tower (TWR) controller to also manage Ground (GND) functions, increasing cognitive demand.
- The safety-critical alert was provided by the pilot of the arriving aircraft and a supervisor, rather than the primary controller's visual scan.
- Management was aware of the visibility obstructions and the high workload but had not implemented sufficient mitigation measures.