Cet article (rédigé en anglais à l’occasion d’un groupe de travail Eurocontrol pour la préparation d’un outil de séquencement Départs & Arrivées) s’adresse aux contrôleurs curieux de savoir comment fonctionne notre séquenceur Maestro, actuellement déployé à Roissy, Orly et Lyon.

VARIOUS CONTROLLERS

In Aix en Provence area center, there are upper and lower sectors with an executive and a planner controller in each sector. Aix ACC has no interaction with Maestro. In Lyon approach room, there are : • 1 MAESTRO controller • 2 INI (“initial approach”) controllers (1 for the Western part of the TMA, 1 for the Eastern) with one assistant controller each • 1 ITM (“intermediary”) controller In the tower, the controllers have no interaction with Maestro.

NORMAL SITUATION

Aircraft are controlled by Aix ACC lower sector executive controller and handed over to the Lyon INI controller a few minutes before reaching the IAF. The INI controller guides all the aircraft in the vicinity of his IAF and hands over the aircraft to the ITM controller before the final axis. The ITM controller gives aircraft the final vectoring for ILS interception and hands over the aircraft to the tower controller on final. With normal traffic, Maestro displays arrivals but is not used or monitored.

HEAVY TRAFFIC SITUATION

During daily hubs, one controller in the approach room activates the Maestro position. This “Maestro” controller reads the sequence proposed by Maestro according to the aircraft time over a point located a few miles before the runway [I’ll give more details below]. He can swap two aircraft in the sequence on his own initiative or on another controller’s request (Aix lower sector, Lyon’s INI or ITM). INI assistants and ITM controller have a simplified Maestro display, so they can know the sequence. An INI assistant can phone an Aix lower sector assistant to indicate the times that the aircraft must meet over the IAF located in this lower sector. This Aix lower sector assistant informs the executive controller who transmits the times to the pilots over the frequency. Some Aix lower sector assistants even retransmit the aircraft times to the upper sector assistants, so that pilots are informed as soon as possible of the time they must enter in their FMS to make the best use of the RTA function.

MAESTRO DISPLAYS

A dedicated Maestro position is used for display and modification of the aircraft sequence. It is manned by the “Maestro” controller. Maestro is also displayed on INI and ITM positions for consultation only. For each aircraft, Maestro displays the callsign, its IAF and the time it is required to meet over this IAF, as well as a time over a point a few miles from the runway. The difference in minutes between this required time and the time the aircraft would have flown is displayed in red (if the aircraft arrives too soon) or green (if the aircraft is late). There is no suggestion of manoeuvre, vectors or speed guidance : only the time the aircraft must gain or lose to meet the required time over the IAF. It is up to the controller to vector or control speed or ask the pilot to use the RTA function. Neither Aix nor Genève ACC have Maestro displays, so phone coordination is needed if Maestro controller wants pilots to be informed as soon as possible in Aix or Genève airspace. Paris ACC (located in Athis-Mons, near Orly airport) has Maestro information : Roissy and Orly Maestros transmit their data to Paris ACC where it is displayed in each of the relevant lower sectors. Paris controllers can read the sequence on a small Maestro text screen and adapt their vectors and speed instructions to comply with the sequence requested by Roissy or Orly Maestro. Tactical swaps are of course possible with a phone coordination with Roissy or Orly INI controllers.

CALCULATIONS

Maestro only has AMAN capability in Lyon, Roissy and Orly. It uses flight plans from Paris or Aix ACC flight plan data processing system to extract callsign, aircraft type, route,… This is not enough for Maestro to calculate a precise time to integrate the aircraft in the sequence. It needs updated radar information. The ACC radar system correlates the Mode A radar signal with a flight plan (offering ACC controllers an enriched radar label) and the approach has a duplicate of the ACC radar display. This allows Maestro to extract the radar position and calculate for each aircraft the times over the IAF and the point close to the runway. According to the airport runways configuration, the Maestro controller enters the corresponding time separation between aircraft. For each known aircraft Maestro then calculates a new time over the point close to the runway and associated time over the IAF. The difference is displayed in green or red to indicate if the aircraft must gain or lose time. If the Maestro controller swaps two aircraft in the proposed sequence, Maestro recalculates automatically the times for these two aircraft (and following aircraft if the swap has an impact on the whole sequence).

DRAWBACKS

An issue with the time horizon in Lyon Maestro is related to the way Maestro acquires radar data to calculate precise times. Flights arriving from Paris or Bordeaux ACCs are known by Aix ACC flight data processing system and radar system long in advance, and radar correlation takes place early enough for Maestro to establish the sequence. The problem is for flights arriving from Genève ACC : their flight plan is well known, but radar correlation in Aix ACC happens only a few minutes before the Swiss/French boundary. It’s only with the radar correlation that Maestro can have a precise estimation of the time over the IAF and the point close to the runway, so Maestro can only integrate this “Swiss” flight among all the long known “French” flights very late. Usually the Swiss flights pop up in the Maestro sequence and provoke a modification of the whole sequence to give room to these flights among the other French flights. Operationally, it is not dangerous but creates an extra workload for the Maestro controller to communicate all the freshly recalculated times. This problem also occurs for short distance flights, even within the same ACC. As long as the short haul aircraft has not taken off, Maestro cannot use any radar correlation to refine this aircraft time schedule. It’s only when the aircraft passes a few thousand feet that the radar correlation happens and Maestro can integrate it in the sequence. Usually, many other aircraft flying to the same IAF have already been given an RTA time, but the short haul aircraft may be geographically ahead of them and require a change in the Maestro sequence so that these aircraft are delayed a few more minutes. Another issue is the wind direction, which is not taken into account by Maestro. It only uses the radar position and speed, and cannot anticipate the speed changes resulting from direction changes along the trajectory. For example, the “Mistral” strong North wind impact on the aircraft ground speed decreases when they turn East by almost 90 degrees during the procedure. Of course the aircraft actual position is updated on the radar, and Maestro can correct its calculations accordingly. Operationally controllers know that during strong wind conditions Maestro times calculations may not be totally exact, and anticipate how they will be corrected.

CONTROLLERS’ IMPRESSIONS

Before Maestro, Lyon controllers only coordinated speed reductions with Aix ACC lower sectors. They would then call Aix ACC lower sectors to ask for specific speed maintenance or reduction, or global speed reductions (“this aircraft at full speed” or “from now on, all aircraft at 250 Kt”). This was not optimal because each lower sector controller vectored his aircraft for his own sector’s IAF in a partial sequence, without consideration for the aircraft on the other IAFs (not under his control). The result was 4 partial sequences from each of the 4 IAFs that the Lyon INI controllers had to integrate into a single global sequence. When Maestro was installed, few teams actually used it but with time more and more teams adopted it. One day the team in Lyon would use the traditional speed procedure, and the next day another team using Maestro would phone Aix ACC lower sectors assistants to communicate the aircraft required times over the IAFs. Today, 7 out of the 8 teams use Maestro, and the last team will soon be “converted”. This transitional phase was very interesting to compare the efficiency of the two methods, which is clearly in favor of Maestro. Aix ACC used to open and manage 2 or 3 stacks during the hubs, but now that Lyon Maestro controller phones Aix ACC to give the required times and that pilots are informed soon enough, the hub peak traffic is absorbed very easily with very rare stack holding. Aix ACC controllers receive more phone calls and may not have the full picture to understand the need for Maestro required times for their own aircraft, but everyone enjoys the simplicity and the efficiency of the new method. With moderate traffic, a lower sector controller will sequence his aircraft for his IAF ; when traffic increases to the point where Maestro requires specific times over the IAF, the controller simply warns each pilot of the time he must comply with over the IAF. The pilot then asks if he can reduce accordingly, and the controller generally accepts. The controller will ask the following traffic for a similar speed reduction. If the second aircraft prefers to stack at normal speed instead of reducing his speed, the controller will not descend them lower than the first aircraft (this is rare because generally all aircraft receive a required time over the IAF that implies a similar speed reduction). Paris ACC controllers use their Maestro display to read the required sequence, which relieves them from deciding themselves and coordinating too much with Orly or Roissy INI controllers. Paris Approach and ACC controllers enjoy the reduction in phone coordinations thanks to the extra Maestro displays in Paris ACC, and most of Aix controllers would like to have a similar display to avoid some phone coordinations with Lyon Maestro controller. One Roissy controller admitted that wouldn’t be possible to handle the same amount of traffic without automatic Maestro sequencing, and a controller in Nice airport, which struggles with limited capacity and problematic stack holding, said she was eager to have Maestro installed in Nice… Surprisingly, Maestro is appreciated by pilots because they now have a precise idea of their delay, compared to the previous uncertainty they felt when radar vectored or arbitrarily reduced in speed by ACC and approach controllers. They have more information and control than before, and they use the RTA function to reduce their workload. But it’s always surprising for a controller to hear a pilot asking “can we reduce 230 Kt ?” !