On Tuesday 2 July, during the parallel approach on runway 36C (Zwanenburgbaan) and runway 36R (Aalsmeerbaan) towards Amsterdam Airport Schiphol, two aircraft approached each other closer than the prescribed separation minima. LVNL conducted its own investigation into this incident and reported the incident to the Onderzoeksraad voor Veiligheid (Dutch Safety Board).
Description of occurrence
An Airbus A330-300 aircraft was approaching from the west to land on runway 36C (Zwanenburgbaan). Coming in from the east, an Embraer 175 aircraft was on approach to land on runway 36R (Aalsmeerbaan). Both aircraft were descending.
There were two approach controllers on duty at the time, one assigned to runway 36C (Zwanenburgbaan) and the other to runway 36R (Aalsmeerbaan). The approach controller had instructed the Airbus to intercept the Instrument Landing System (ILS) at an altitude of 1,200 metres (4,000 feet) for a landing on runway 36C (Zwanenburgbaan). The Airbus had carried out this task as instructed. The Embraer was flying at an altitude of 900 metres (3,000 feet) and was instructed by the other approach controller to intercept the ILS of runway 36R (Aalsmeerbaan). According to the procedure followed in this situation, there was sufficient distance in altitude (vertical separation) between the two aircraft (300 metres/1,000 feet).
The approach controller of runway 36R (Aalsmeerbaan) noted that the Embraer did not intercept the ILS of runway 36R (Aalsmeerbaan). For that reason, the traffic controller instructed the pilot to make a right turn to a north-northeast heading to intercept the ILS from the other side. Initially, the pilot did not respond to this instruction. The approach controller repeated the instruction, after which the Embraer pilot responded and carried out the course correction. Meanwhile, the Airbus had started the descent according to the ILS glide path to runway 36C (Zwanenburgbaan). As the Embraer had not yet intercepted the ILS, there was insufficient difference in altitude between the aircraft; this is called a separation breach. The approach controllers contacted each other about the situation and agreed on how to achieve a safe distance between the aircraft. To that end, the approach controller assigned to runway 36R (Aalsmeerbaan) instructed the pilot of the Embraer to descend to 600 metres (2,000 feet) and provided information about the position of the Airbus. The Embraer then flew away from the Airbus on a divergent heading. After this, the Embraer intercepted the ILS of runway 36R (Aalsmeerbaan) and sufficient distance between the aircraft was achieved.
Both aircraft landed safely.
During this occurrence, the minimum distance between the two aircraft was 3.5 kilometres (1.9 nautical miles) horizontally and more than 180 metres (600 feet) vertically. The standard at that stage of the flight was 300 metres (1,000 feet) vertical. At the moment of minimal separation, the Embraer flew away from the Airbus on a divergent heading. Shortly after the moment of minimal separation, both aircraft were stabilised on the ILS for their landing runway. By then, sufficient safe distance had been established between the two aircraft.
Conclusions of the investigation and follow-up actions
The investigation into this occurrence showed that the pilots of the Embraer had forgotten to select the approach mode of the flight control computer to intercept the ILS. This prevented the aircraft’s on-board computer from intercepting the ILS. The aircraft continued on the intercept heading. Because it took some time before the Embraer started the corrective heading, the Airbus had meanwhile started the descent according to the ILS glide path. Because of this, there was insufficient difference in altitude. The approach controller restored the distance between the aircraft by providing additional altitude instruction and information about the position of the Airbus.
Based on comparable occurrences, LVNL conducted an internal investigation to thoroughly analyse all underlying causes of occurrences with parallel approaches at Schiphol Airport. The results of the investigation led to the implementation of a number of improvements, such as paying extra attention to the specific procedures for parallel approaches among air traffic controllers as well as pilots, researching technological options for providing further support to air traffic controllers, and more detailed monitoring of the parallel operation to learn from the resulting observations.
Classification: significant occurrence