Dan Ivanescu

Models of Air Traffic Merging Techniques: Evaluating Performance of Point Merge

A new technique, Point Merge, for merging aircraft without vectoring in terminal areas (TMA), is modelled, and used in fast-time simulatio ns. Four arrival traffic streams are merged for landing on a single runway. A method for designing fast-time models of vectoring and Point Merge is proposed and validated using real-time simulation trajectories. Relative performances of fast-time simulations of t he corresponding models are compared. Interactions with departure traffic are also assess ed. Results show the Point Merge model reduces: mean controller task load (20±1%), the number of instructions to pilots (~30%), and fuel consumption (170±14 kg), compared with vectoring.

Effect of aircraft self-merging in sequence on an airborne collision avoidance system

This air traffic management research study analysed the interaction between a potential future airborne spacing application and an existing Airborne Collision Avoidance System (ACAS). The time-based airborne spacing application ‘merge behind’ was simulated in fasttime for a range of merge angles (45°, 90°, 135° and 180°), target spacing times (60 and 90 s) and altitudes (6,000 and 11,000 feet) under turbulent wind and extreme entry conditions. Trajectory pairs were analysed for potential collision alerting conditions using an ACAS simulator based on Traffic Alert and Collision Avoidance System (TCAS) II version 7 logic. Results show how, with realistic turn anticipation, the TCAS estimated time to go to Closest Point of Approach (CPA) decreased as merge angle was increased and as target spacing was reduced, but still remained above the Traffic Advisory (TA) and Resolution Advisory (RA) thresholds for the duration of all trials.

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

The objective of this air traffic management study was to analyse the trade-off between time spacing accuracy and corresponding control effort in a potential future application of airborne separation assistance systems (ASAS). The ASAS application airborne spacing sequencing and merging was simulated in fast-time. Lead aircraft speed profiles were generated using complete descent profiles from real-time experiments. For validation purposes, three metrics were derived from real-time experiments: time spacing error (accuracy), frequency of speed adjustments (control activity), and cumulative airspeed variations (control cost). Four experimental parameters were varied: automatic and manual speed control, spacing dead-zone, guidance law dynamics time constant and initial time spacing error. A trade-off between the metrics was found for a sequence of two aircraft by comparing their variation with the experimental parameters. Corresponding ‘minimum’ performance requirements for the metrics are proposed: (i) time spacing error - mean less than 1.5s with 0.5 to 85% of the values between -4 and +4s (automatic mode), and mean less than 2.5s with 0.5 to 85% of the values between -6 and +6s (manual mode), (ii) frequency of speed adjustments - mean less than 1 action per minute (manual mode) and (iii) cumulative airspeed variations - mean less than 10 knots (automatic and manual modes). These requirements form a basis for investigating sequences longer than two aircraft where chain propagation effects may lead to additional constraints.

Impact of ADS-B Link Characteristics on the Performances of In-Trail Following Aircraft

In the general context of the delegation of some controller tasks to the flight deck, the pilots could be instructed to adjust its aircraft speed so as to maintain a prescribed longitudinal spacing with respect to the aircraft flying ahead. ADS-B (Automatic Dependent Surveillance – Broadcast) technology is one of the potential key enabler to support the implementation of such application. In this paper, the relationship between the ADS-B surveillance data characteristics (information exchanged, update rate, latency, accuracy) and the performance of the in-trail following aircraft application (stability of the in-trail aircraft, expected accuracy of in-trail aircraft time or distance spacing) is investigated based on a mathematical model of the in-trail aircraft.

Effect of Entry Conditions on Airborne Spacing when Sequencing Multiple Converging Aircraft

This air traffic management research study analysed the range of admissible entry conditions for using airborne spacing to sequence aircraft on multiple trajectories merging at a fixed waypoint. A guidance law was developed capable of merging multiple aircraft in descent under turbulent wind conditions. Effects of initial distances and speeds on the ability of an aircraft to descend from 29,000 to 3,000 feet and establish a stable spacing (8 NM) behind another by a given merge point were measured using fast-time simulations. Results for two aircraft at the same initial speed (272 knots calibrated airspeed) show how the possible initial spacing error envelope grew from [-0,+0] to [-22,+25] NM when the initial distance of the lead aircraft to the merge point was increased from 0 to 100 NM. The impact on initial spacing error of varying the difference in initial speed from –60 to +50 knots between the two aircraft was slight (magnitude less than 5 NM). Results for three aircraft of similar initial speeds are presented as contour maps to show how the initial spacing error envelopes of the second and third aircraft grew with initial distance of the lead aircraft to the merge point.

EFFECT OF MIXED AIRCRAFT TYPES AND WIND ON TIME BASED AIRBORNE SPACING

This air traffic management research study analysed the performance of constant time based airborne spacing under different operational conditions using fast time simulation. The effects of mixed aircraft types and wind conditions on the ability of an aircraft to maintain a constant time delay along-track spacing behind a descending lead aircraft were investigated. An exact constant time delay (60 s) spacing criterion based on lead aircraft position history was used to compare the spacing performance of all combinations of heavy and light aircraft for different wind conditions. Results show for both constant and turbulent winds that cross-track winds could have just as detrimental an effect on along- track time based spacing performance as along-track winds. Turbulent winds severely degraded time based spacing stability particularly in cross and head wind conditions. Tail winds were the least disturbing for time based spacing in both constant and turbulent cases. A heavy aircraft following a light tended to produce the maximum spacing errors. The other three combinations of aircraft type resulted in similar maximum spacing error behaviour.

Aircraft Punctuality at Arrival Terminal-Area: Impact on Sequence Conformance, Saturation and Cost

Aircraft arrival punctuality is a key performance measure of the Single European Sky Air Traffic Management Research (SESAR) target concept. A large source of uncertainty in landing times today is due to the merging of poorly synchronised traffic streams in the terminal area (TMA). The objective of this collaborative study was to evaluate benefits of aircraft accurately controlling their own entry time in to the arrival terminal area. Probabilistic modelling is used to investigate the air traffic control performance benefits of aircraft respecting a Controlled Time of Arrival (CTA) at an initial approach fix (IAF~10,000 feet) agreed up to about one hour before with an accuracy of ±10s, 95% of the time. Results indicate the probability of a sequence of CTAs all being met within a tolerance of ±30s, greatly increases with proportion of aircraft RTA equipped. RTA equipage enables CTA sequences to be met for arrival control horizon times much longer than today with an air traffic controller using an arrival manager. The risk of a busy TMA saturating or having to re-sequence due to bunching at the IAF is reduced by orders of magnitude when all aircraft are equipped with RTA. Extended arrival control horizon times enabled by RTA allow delay absorption by speed control instead of path-stretching resulting in fuel savings increasing (relative to a controller without an arrival manager) from 110±10kg at 15 minutes to 150±25kg at 70 minutes.