Airborne Spacing: Managed vs. Selected Speed Mode on the Flight Deck

Abstract

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).

Towards Performance Requirements for Airborne Spacing- A Sensitivity Analysis of Spacing Accuracy

“…The time-based airborne spacing 'Merge behind' application involves an air traffic controller instructing a pilot to select a neighbouring aircraft as a target on a Cockpit Display of Traffic Information (CDTI). An example of the phraseology developed [9] is:…”

“…where constant t is the guidance time constant that defines the guidance dynamic. Note that this algorithm was validated in real-time experiments (see [9]).…”

“…The scenario used in real-time experiments [9] and replicated in Matlab was as follows: the lead aircraft speed profile in cruise is representative of a chain effect (4 aircraft with initial spacing alternatively too small then too large). Preceding pilots had a quick reaction time and thus could anticipate the speed reductions.…”

“…A real time experiment was conducted on an Airbus A320 fixed-based cockpit simulator to investigate the use of a speed managed mode (automatic) for airborne spacing [9]. The speed managed mode was found to be the most appropriate during the initial descent (as it reduced workload) but some preferred the speed selected mode (manual aided by airborne spacing director) during final approach to respect airline recommendations or to keep the control of their speed in this critical phase.…”

Airborne Spacing: Flight Deck View of Compatibility with Continous Descent Approach (CDA)

“…The air experiments conducted in 2004 and 2005 considered the complete descent phase with the preceding aircraft under airborne spacing and assessed the effect of different positions in the chain in simulating varied target speed profiles 12 . The subsequent air experiment conducted in 2005 in a fixed based cockpit simulator aimed at going a step further by assessing the use of a speed managed mode from cruise until automatic disengagement at 2000ft 14 . From all these experiments, pilots reported benefits in terms of situation awareness, accuracy of spacing, reduction of communications, but expressed concerns in terms of flight efficiency.…”