|
|
|
|
4D trajectory management: an initial pilot perspective |
|
|
|
A real-time simulation investigated the feasibility of 4D trajectory management en-route from the perspective of the pilot. Adherence to a reference business trajectory time constraint (-2 minutes; +3 minutes) caused no difficulty. A controlled time of arrival window (±30 seconds) was slightly more difficult to achieve and required closer coordination between pilots and controllers. The findings from this simulation and from a ground simulation will be used to help refine the 4D trajectory management concept in the context of SESAR.
|
|
|
|
4D Trajectory Management in SESAR |
In the context of SESAR, 4D trajectory management is expected to improve air traffic operations, in particular to increase the overall predictability of traffic, with benefit to airlines and air traffic management. The concept relies on a reference business trajectory (RBT) which the airspace user agrees to fly and the service provider agrees to facilitate (subject to separation provision). It implies a target time of arrival over a waypoint of the trajectory, e.g. the initial approach fix (IAF), within a time window tolerance. However, in busy airports during peak hours, the RBT time window tolerance (-2min; +3min) may not be accurate enough to ensure an efficient pre-regulation of traffic and to optimise the runway capacity. In that case, the aircraft could be tasked to achieve a Controlled Time of Arrival (CTA) at the IAF with a refined time tolerance window (±30s).
Several projects (e.g. PHARE, AFAS) were conducted to assess 4D trajectory concepts and capabilities from both air and ground perspectives. Some flight trials were also conducted to evaluate the use of the 4D Flight Management System (FMS). A real-time simulation, held in March 2007 at the Experimental Centre, investigated 4D trajectory management in an en-route environment from the perspective of the air traffic controller. Allowing aircraft to adhere to their preferred 4D trajectories enhanced flight time predictability, but impacted controllers’ tasks.
To go a step further, a flight deck experiment was conducted in December 2007. The objective was to perform an initial assessment of the operational feasibility of the management and the execution of a Reference Business Trajectory and a Controlled Time of Arrival from a pilot’s perspective.
|
|
|
The simulation was conducted over a period of one week and involved eight pilots from European airlines and from an aircraft manufacturer. These pilots made up four crews and each crew participated in the simulation for one day. The airspace chosen was a subset of the current Maastricht airspace as used in the en-route ground simulation. It comprises three busy high level en-route sectors: Delta, Ruhr and Munster.
The flights started in cruise and included initial descent (to a minimum FL260); they lasted approximately 40 minutes. Adherence to the trajectory was expressed as the degree to which a time constraint at a specific waypoint was respected. The tolerance window was set to (-2min; +3min) by default (RBT) and to ±30s for a CTA. The time constraint was set on the last waypoint of each scenario (Figure 1).
|
 |
| Figure 1. Overall description of scenario |
|
|
|
|
Pilots were exposed to typical situations in which aircraft deviate from the planned trajectory; these situations were derived from the preceding ground experiment. The situations selected involved deviation from RBT or CTA. The deviation was caused by the entry conditions and could be exacerbated by ATC intervention for separation purposes. The three resulting runs were:
- Run 1: aircraft enters the airspace with 2 minutes to lose with respect to its RBT.
- Run 2: aircraft enters the airspace with 1 minute to gain with respect to its CTA.
- Run 3: initially the aircraft enters the airspace with 30 seconds to gain with respect to its RBT. Subsequently (see Figure 2) a CTA constraint is issued requiring the aircraft to gain a further 30 seconds.
|
|
|
 |
| Figure 2. Timeline description of one of the runs |
|
|
|
|
The experiment was conducted on an Airbus A320 fixed based simulator, equipped with an emulation of the current Honeywell RTA function (Figure 3). Each flight was immersed in a previously recorded scenario with background traffic. Flight crews were tasked to fly the simulator as they would do in a regular flight, performing their usual tasks, including communications with ATC and checklists. Navigation charts, and checklists were provided. The pilots were instructed to respect the time constraint with the support of the RTA function. The strategy to adhere to the time constraint was left to the pilots’ discretion, who could use speed (managed or selected) or lateral (e.g. direct) manoeuvre (request to ATC).
|
 |
| Figure 3. RTA function, in selected (left) and managed (right) speed modes |
|
|
|
|
Four dimensions were considered for analysis: feasibility, workload, effectiveness and foreseen benefits and limitations. These dimensions were addressed using both subjective data (observers’ notes, questionnaires and debriefing items) and objective data (aircraft data and pilots’ actions).
|
|
|
|
In the simulated situations, the pilots found adherence to 4D trajectories to be feasible in cruise: gaining or losing time in order to respect an RBT time constraint (-2min; +3min) caused no difficulty. The tighter CTA tolerance window (±30s) was reported slightly more difficult to achieve and required closer coordination between pilots and controllers. Pilots suggested they should be in charge of speed control, and the controllers should facilitate or propose lateral changes if speed adjustments were not sufficient.
As anticipated, improvements to the current RTA functions are required. The computation of the managed speed as well as estimated times of arrival should be enhanced to increase the robustness of the guidance, especially during descent. Moreover, additional support (late/early indication on the navigation display, and a “what if” tool) were requested for monitoring and selecting appropriate action.
Although 4D trajectory management implies an additional task on board, especially for the pilot flying, this was felt to be an acceptable increase of workload in cruise. However, in the case that the RTA cannot be met, renegotiation would potentially cause a larger workload increase. As anticipated, most of the pilots agreed that they would rather use only speed to lose time whereas both speed and lateral actions could be required to gain time (Figure 4). Despite large differences between individuals, the limitations of the current RTA function might explain the large use of the selected speed mode.
|
 |
| Figure 4. Pilots' preferred strategy to adhere to 4D trajectory |
|
|
|
|
|
In terms of effectiveness, objective results show that all the flight crews always achieved both RBT and CTA time constraint within the tolerance windows (Figure 5).
|
 |
| Figure 5. RTA accuracy over the time constraint waypoint per run |
|
|
|
|
Despite the induced speed variations, the pilots thought that the flight efficiency was similar to today. Speed variations lead to an increase in fuel consumption, although this could be improved by smoother speed guidance. Reduction in holding or vectoring later in the approach area should lead to gains in fuel efficiency.
Most of the pilots agreed that 4D trajectory management could provide a better predictability of traffic flows (for traffic management) and of arrival times (for airlines) assuming adequate planning before take-off. However, the pilots expressed some doubts concerning the overall efficiency of the system since unexpected events (weather, boarding delays, separation provision…) may trigger many renegotiations of the RBT. |
|
|
|
This simulation was made in the frame of the European ATM Validation Platform (EVP) programme from EC DG-TREN.
|
|
|
|
| |
|
 |
|
Last validation: 23/06/2008
|
|
|
|
|
|
|
|
