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Airspace Infringement of Class D Airspace – Stansted Control Area 4 and Luton Control Area 1

Date 26 September 2020
Aircraft Category Fixed-wing Aeroplane
Type of Flight Recreational Flight
Airspace/Class Stansted & Luton CTA / Class D

The Air Traffic Controller

The Air Traffic Controller reported that they had traffic on a right-base for Runway 25 at London Luton Airport descending to 3,000 feet. A radar contact was seen to climb into controlled airspace south of Royston passing 2,600 feet before stopping the climb at 3,000 feet on an approximate track of 250o. Traffic information was passed to the Luton arrival aircraft and it was turned onto a shorter final to avoid the infringing aircraft. At this point the unknown aircraft selected 0013 squawk and the controller was able to ascertain their callsign and get 2-way communication with him. The pilot informed the controller they were leaving controlled airspace to the north which they subsequently did. The aircraft was then identified and given a service as per the pilot’s request. The Luton arrival was then re-vectored and completed a safe approach to land.

The Pilot

The pilot reported carrying out a recreational flight from Duxford to Cornwall via Wing (west southwest of Leighton Buzzard) to route to the north of the Luton Control Zone. The route was planned to be flown at 3,000 feet to remain below the CTAs with a lowest base of 3,500 feet. The plan was to climb straight ahead to 3,000 feet on a heading of 251o after departure from Runway 24 (Figure 1).

Figure 1

Figure 1

On the morning of the flight there was a strong northerly wind flow down the east side of the UK. The associated TAF were as follows:

  • Stansted: 300/14, PROB 40 TEMPO 2606/2609 32018G28
  • Luton: 300/14, TEMPO 2606/2706 33018G28.
  • The forecast 2,000 feet wind at 5230N 00E was 340/35 (35 knots at 90o to the planned track)

Just before departure an aircraft called Duxford Information to state they would be conducting visual circuits at Fowlmere (2.5NM west southwest of Duxford). On lining up for departure the pilot was informed of the traffic at Fowlmere and the surface wind “being something like 310/16”.

On climb out the pilot encountered the most vigorous turbulence that they could recall flying in for many years. They elected to hold runway heading as best they could to climb straight ahead out of the ATZ without turning right to the track of 251o degrees to enable them to remain clear of Fowlmere (blue line in Figure 2); the passenger was asked to look out for the Fowlmere circuit traffic. Given the turbulence, the pilot elected to climb at best rate of climb speed, which was approximately 80 knots, with the aim of getting into smoother air as soon as possible.

Once clear of Fowlmere, the pilot called Duxford to leave their frequency, changed to Luton Radar on 129.550 MHz and then selected the Luton Frequency Monitoring Code (FMC) of 0013. With the long nose of the aircraft, forward visibility is limited when climbing steeply; unfortunately, that meant fewer visual cues as to actual track were available to the pilot. As the aircraft approached 3,000 feet the pilot asked the passenger to pass them their Moving Map tablet that had been running since departure. The pilot was just noting they had had flown to the left of the airspace line (magenta line in Figure 2) when Luton Radar called to advise that they were indicating at 2,800 feet and was advised immediate descent to below 2,500 feet. Realising their error, the pilot responded that they were descending and turning north to head out of the Stansted CTA as quickly as possible.

Figure 2

Figure 2

ATC aspect

The airspace and track where the aircraft infringed is routinely used by Luton and Stansted traffic. This incident took place when the traffic was light and therefore the consequences of the infringement was minimal. Following agreement with the pilot of the arriving aircraft the controller re-positioned the aircraft and ensured minimum separation was achieved between the two aircraft However, in normal traffic levels with a continuous stream of arrivals the ability to reposition the aircraft without any impact on subsequent arrivals is unlikely. The workload increase for pilot and controller is significant under these circumstances with safety remaining paramount. One infringement of only a few minutes can result in many minutes of delay to operators, with additional fuel burn and emission also a consideration.

Causal Factors/Findings

The pilot carried out detailed and effective planning in route selection to remain outside controlled airspace and included the use of FMC along the route. In addition, they were equipped with a Moving Map which was intended to be used actively en-route. They also recognised the Threat associated with dual operations at Duxford/Fowlmere.

However, a minor change to the plan moments prior to departure allowed the introduction of lapses in wider Threat and Error Management. The decision to fly further south in strong cross winds and to climb at a higher rate resulted in the aircraft’s track being affected greater over a shorter distance the aircraft drifting further south of track than had been anticipated. The pilot, unaware of their ground track due to reduced forward visibility associated with the aircraft’s attitude then lost situational awareness and extended beyond that required to avoid the traffic flying circuits to the north of Fowlmere. By the time the aircraft was south abeam the Runway 25 threshold at Fowlmere, it was 1.2NM south and passing 1,500 feet. In addition, had the pilot identified that routing to the south of Fowlmere would take them closer to the Class D CTAs they may have identified the increased value to using the Moving Map. This would have enabled them to regain situational awareness lost through the aircraft’s attitude. The pilot could have either turned right back onto track or stop their climb below 2,500 feet to remain below the CTA. However, the pilot was faced with several distracting factors from their original plan and their capacity was rapidly being used in handling the aircraft in extremely turbulent conditions whilst considering the traffic at Fowlmere and the wellbeing of their passenger.

In their wider plan, the pilot had considered the Take 2 aspect to remain clear of controlled airspace but that was not revised following the amended plan to deviate to the south of Fowlmere and thereby fly close to the CTA. Had the pilot only climbed to, for example 2,300 feet, until closer to Royston, the infringement could also have been avoided. This probably did not enter the pilots thought process as the focus was on climbing out of the turbulence, avoiding the Fowlmere visual circuit, and selecting the next radio frequency and FMC.

Notwithstanding the lapses in Threat and Error Management, the pilot’s initial plan was good and incorporated several key measures to prevent airspace Infringements:

  1. Comprehensive planning including airspace avoidance and meteorology;
  2. Use of a Moving Map; and
  3. Use of an FMC.

That decision to use an FMC enabled early intervention by air traffic control to assist the pilot and resolve the situation promptly. In addition, detailed post-occurrence analysis and open and detailed reporting by the pilot enabled lessons to be identified to avoid a recurrence.

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Other narratives in this series can be found on the Infringement occurrences page

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