Introduction
On June 26, 2023, at approximately 15:47 UTC, a loss of separation occurred at Porto Airport (LPPR), Portugal, involving a Boeing 737-800 (registration EI-DLX) and an Airbus A321neo (registration CS-TSI). The event was classified as an AIRPROX incident by the Portuguese Aviation Accident Investigation Authority (GPIAAF).
Event Description
The Airbus A321neo, operated by Sata, had been cleared by air traffic control to line up on runway 35 after a preceding aircraft landed. The A321 entered and lined up on the runway at 15:45:06, awaiting take-off clearance. Meanwhile, a Boeing 737-800, operated by Ryanair, was on final approach to the same runway and had been instructed to reduce speed to minimum approach speed.
At 15:46:53, less than 30 seconds from landing, the Boeing 737 pilot contacted the tower controller. The controller issued wind information and landing clearance. However, the Boeing pilot noticed the runway was occupied by the Airbus and alerted the controller, stating "just confirm there is an airplane on the runway." The controller then instructed the Boeing to go-around approximately 13 seconds before crossing the runway threshold, cancelling the landing clearance.
Data showed the Boeing descended to 275 feet above ground level (AGL) at a distance of 950 meters from the runway start, where the A321 was located, before it began to climb. After the A321 took off for Porto Santo and traffic normalized, the Boeing conducted a new approach and landed without further incident.
Traffic Conditions
Prior to the event, Porto Airport experienced intense ground movement. Between 15:47 and 16:00, ten take-offs were planned and sequenced, with six aircraft on the ground in contact with the tower and three in flight. Activities included multiple push-backs, a request for cross-bleed engine start, an arriving aircraft that overshot its stand, and three vehicles on the movement area: a Follow-Me vehicle scheduled for runway inspection, a maintenance vehicle obstructing a taxiway, and another maintenance vehicle on taxiways Sierra. These required coordination by the tower controller.
Tower Setup
At the time, all operational positions at Porto Tower were manned: Approach/Area Control (APP), Clearance Delivery (DLV), and Aerodrome Control (TWR). The TWR controller also handled ground (GND) functions, contrary to typical practice at larger aerodromes where these roles are separate. The entire team of five controllers was on duty; two were on break while three manned positions, with a temporary supervisor present. The TWR controller was primarily focused on visual traffic coordination due to the busy environment. When the Boeing pilot called on short final, the controller visually checked the runway before issuing clearance but was immediately alerted by both the temporary supervisor and the Boeing pilot about the A321's presence.
Consequences
There were no injuries or damage to either aircraft as a result of the incident.