A new allocation of tasks between controller and flight crew is envisaged as one possible option to improve air traffic management and in particular the sequencing of arrival flows. It relies on a set of new spacing instructions where the flight crew can be tasked by the controller to maintain a given spacing with respect to a designated aircraft. In order to assess the benefits and limits of airborne spacing, two streams of air and ground experiments were conducted. The latest air experiment aimed at assessing the feasibility of time-based spacing in final approach and its impact on flight crew activity. Flight crews were tasked to maintain a spacing behind a target aircraft, through adjustments of the selected speed. Their feedback on feasibility was generally positive despite an increase of mental effort which remained acceptable. Every crew successfully achieved the spacing task: the deviation was maintained within the tolerances. The impact on flight crews' activity was assessed through the speed actions needed to perform the spacing task. The average number of speed actions was less than 1 per minute, and most were small adjustments comprised between -15kt and +5kt. The effect of various reactions of preceding aircraft under airborne spacing will be investigated in further experiments, as well as monitoring load and scanning pattern.

To assess the benefits and limits of a new spacing instruction from flight crew perspectives, a pilot-in-the-loop experiment was conducted. Beyond assessing interface usability and overall feasibility, the experiments aimed at analysing the impact of various tolerance margins on flight crew activity and efficiency. Flight crew feedback was generally positive. Despite a new task in the cockpit, which requires appropriate assistance to contain workload, pilots highlighted the positive aspects of getting in the loop, understanding their situation (through goal-oriented instructions), and gaining anticipation. Results showed that even though the smallest tolerance margin (0.25NM) led to increased workload, the spacing deviation was usually below 0.5NM.

This paper reports on an experiment conducted with airline pilots on a fixed-based cockpit simulator. The objective was to assess the use of a speed managed mode for airborne spacing, compared to a speed selected mode. The availability of a speed managed mode reinforced the pilot acceptability. All pilots found airborne spacing feasible and compatible with their usual flying task, from cruise until automatic disengagement at 2000 feet. The speed managed mode was found as the most appropriate during the initial descent but the speed selected mode was preferred by some pilots during final approach. The spacing was well maintained below the 5 seconds tolerance margins with an average of-0.1 second and a 95% containment within ±2.5 seconds. The cost induced is in the order of 60 knots additional speed changes for the complete descent phase, with a maximum but also a minimum cost when using the speed selected mode. This raises the issue of trade-off between required performance (spacing accuracy) and cost induced (speed changes).

To assess, from flight crew perspectives, the benefits and limits of a new spacing instruction, a pilot-in-the-loop experiment was conducted. Beyond assessing interface usability and overall feasibility, the experiment aimed at analysing the impact of various tolerance margins on flight crew activity. Flight crew feedback was generally positive. Despite a new task in the cockpit, which requires appropriate assistance to contain workload, pilots highlighted the positive aspects of getting in the loop, understanding their situation, and gaining anticipation. Results showed that the average spacing deviation was usually below 0.5NM.

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