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On Saturday, June 28, 2025, two aircraft came closer to each other than the separation minima prescribe. One aircraft was an inbound flight heading to Rotterdam The Hague Airport, the other was an inbound flight heading to Amsterdam Airport Schiphol.
LVNL conducts its own investigation into the occurrence and has also reported it, in accordance with the investigation process, to the Dutch Safety Board, the Human Environment and Transport Inspectorate, and the Public Prosecution Service.
The Amsterdam Area Control Center (ACC) guides aircraft at altitudes ranging from approximately 1.7 to 7.5 kilometers. They ensure that aircraft remain safe and maintain sufficient distance from one another. Minimum separation requirements apply: 5 nautical miles (approximately 9.3 kilometers) horizontally or 1,000 feet (approximately 300 meters) vertically. The air traffic controller monitors these distances and, when necessary, issues instructions regarding altitude, heading, and speed, among other things.
Various traffic flows pass through ACC Sector 3, including traffic to and from Schiphol and Rotterdam. Just as the ACC air traffic controller is guiding traffic toward Rotterdam, two other aircraft check in on the frequency: a Boeing 737-900 (B739) en route from Brussels to Amsterdam Airport Schiphol and a Boeing 737-800 (B738) en route to Rotterdam. The air traffic controller guides both aircraft to their destinations.
At one point, the B738 is at flight level 160 (approximately 4.9 kilometers in altitude) and the B739 at flight level 140 (approximately 4.3 kilometers in altitude). When the B738 requests permission to descend further, the air traffic controller grants permission to descend to flight level 130 (approximately 4 kilometers in altitude). Shortly thereafter, the air traffic controller notes that the flight paths of both aircraft are crossing. To maintain sufficient vertical separation between the aircraft, the air traffic controller issues a corrective course instruction to the B738 and instructs it to halt its descent at flight level 150 (approximately 4.6 kilometers in altitude), thereby maintaining the required vertical separation of 1,000 ft (approximately 300 meters) from the B739 at flight level 140.
The air traffic controller expects that these instructions will maintain the required vertical separation of 1,000 ft. However, the B738 appears to be descending more rapidly from flight level 160 and, while attempting to halt its descent, consequently passes below the assigned altitude of flight level 150. The aircraft descends to flight level 144 before beginning to climb again.
The air traffic controller notices this and issues the B739 an additional course instruction to turn right, thereby increasing the distance from the B738. Thanks to these additional instructions, the situation remains under control. However, the minimum separation standard is breached.
The minimum distance between the two aircraft was 2.8 nautical miles horizontally (nearly 5.2 kilometers) and 600 feet vertically (just over 180 meters).
ACC air traffic controllers apply separation criteria in this area of 5 nautical miles (approximately 9.3 kilometers) horizontally or 1,000 feet (approximately 300 meters) vertically.
The incident was investigated by LVNL, in consultation with the airlines involved.
The incident occurred after the ACC air traffic controller issued an instruction without immediately noticing the conflict between the flight paths of the B738 and B739. Shortly thereafter, the air traffic controller corrected the situation. However, at that moment, the B738 was already descending too rapidly to be stopped at the intended altitude. The air traffic controller was also busy handling several other aircraft en route to Rotterdam. After determining that the altitude instruction was insufficient, the air traffic controller issued an additional course instruction to the B739 to mitigate the severity of the separation breach.
The incident was reported to and discussed in detail with the air traffic controllers involved. During this discussion, they reflected on the events leading up to the incident and the combination of factors that played a role. Those involved acknowledge the conclusions of the investigation and have learned lessons from the situation.
The investigation did not identify any causes that would require structural changes to the system. The safety nets in place functioned as intended in this situation. The ACC air traffic controller was alerted to the situation by a so-called STCA (Short-Term Conflict Alert) notification on the radar screen. This notification drew attention to a potential separation violation.
The pilots of both aircraft also stated that they had visually observed the other aircraft and thereby determined the distance between them. In addition, the distance between the aircraft was sufficient to prevent any warnings from the safety systems (TCAS) from being triggered in the cockpit.
Classification: major incident
