Notice
On Monday, July 1, two aircraft breached the separation minima in controlled Dutch airspace over the North Sea (Amsterdam FIR) in which air traffic services have been permanently delegated by LVNL to a UK air navigation services provider.
LVNL is investigating this incident and has reported it to the Dutch Safety Board, Public Prosecution Service and the Human Environment and Transport Inspectorate.
Situation and investigation
An Embraer E190 takes off from Runway 24 at Schiphol Airport with destination London City. The aircraft is transferred by the Schiphol approach controller to area radar control, which instructs the pilot to climb to FL200 (approx. 6.1 kilometres ASL). This is the maximum altitude at which the aircraft will fly to London City. In addition, the radar controller gives instructions to fly directly to 'ABNED’, one of the coordination/changeover point points (COP) at which traffic must be transferred to UK air traffic control.
LVNL has standard agreements with each neighbouring foreign Air Navigation Services Provider (ANSP) that are laid down in a Letter of Agreement (LOA). Under these agreements, it is standard practice to transfer outbound flights between LVNL Area Control Centre (ACC) and NATS London Terminal Control (LON TC) via 'ABNED' at FL200.
With the Embraer E190 still well within Dutch airspace, at FL200, LON TC coordinates with ACC about a Boeing 737-800 departing from London Stansted bound for Eindhoven and flying at FL190 (approx. 5.8 kilometres ASL) towards the COP 'REDFA'. LON TC asks ACC permission to the direct the Boeing 737-800 from its current position to navigation point 'TUPAK'. TUPAK is a COP in Dutch airspace between ACC and Military Air Traffic Control. The flight paths of the Embraer E190 and the Boeing 737-800 will cross each other, but because the two aircraft meet the minimum vertical separation criteria in ACC airspace of 1000ft (about 300 metres), the request is approved by ACC.
Soon after, the Embraer E190 pilot is instructed to switch to the frequency of LON TC. Three minutes later, the Boeing 737-800 is transferred by LON TC to Amsterdam ACC and contacts the Amsterdam ACC radar controller. The lateral separation between the aircraft at that time is about 40 nautical miles (74 kilometres) at this point, with an altitude difference of 1000ft (300 metres), while the Embraer E190 is still in Dutch airspace and the Boeing 737-800 in UK airspace.
A few minutes later, both aircraft fly into a segment of Dutch airspace in which air traffic control responsibility has been delegated to LON TC. This airspace, the 'AMRIV area', is located in the most south-western part of Dutch airspace and has been delegated to LON TC to safely and efficiently handle traffic to and from airports around London in particular.
The horizontal separation between the Embaer E190 and the Boeing 737-800 is now 10 nautical miles (18.5 kilometres). As the aircraft are flying in opposite directions, their lateral separation quickly reaches the 5-nautical-mile minimum (9.2 kilometres), with the 1000ft (300 m) vertical separation initially ensuring proper separation. Separation criteria dictate that aircraft must at all times be laterally separated (5 nautical miles) or vertically separated (1000 ft). In this case, the Embraer E190 heading for London is set to fly above the Boeing 737-800 heading for Eindhoven with 1000 ft separation.
According to separation standards, the Embraer E190 would be allowed to descend once it had flown 5 nautical miles past the Boeing 737-800. However, shortly after the aircraft have passed each other but before lateral separation exceeds the prescribed 5 nautical miles (9.2 kilometres), the Embraer E190 starts its descent following instructions from the LON TC controller, thus breaching the separation minima. ACC notes this anomaly and coordinates with LON TC, where it becomes clear that the LON TC controller gave an incorrect instruction to the Embraer E190. No action is required from ACC, LON TC or the pilots to expedite recovery of the situation.
Minimum separation
The minimum separation between the Embaer E190 and the Boeing 737-800 is 2.9 nautical miles (5.4 km) horizontally and 500ft (150 m) vertically. Separation was restored within a minute as the aircraft passed each other, creating 5 nautical miles (9.2 kilometres) of separation.
Conclusion
This incident was shared with the NATS safety department and one internal recommendation was issued after the investigation to help prevent such situations in the future.
Classification: Major Incident
