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Airborne Precision Spacing

Airborne precision spacing has been developed by the National Aeronautics and Space Administration (NASA) over the past seven years as an attempt to benefit from the capabilities of the flight deck to precisely space their aircraft relative to another aircraft. This knowledge has been studied for over 40 years with the aim to improve arrival in terminal area operations. Airborne precision spacing consists of an air traffic controller instructing an aircraft to achieve an inter-arrival spacing interval on the runway, in parallel to another aircraft. Flight crew will often use airborne automation to achieve this. Airborne precision spacing is used to keep speed within suitable limits and promote system wide stability (Barmore, 2006).

History and research background

NASA experimented with Airborne precision spacing using simulator technology. They found that pilots could use information displayed airborne-managed spacing. This research also determined that time-based spacing was more effective than distance-based spacing, this is due to the speed reductions seen in arrival flows (Williams, 1983). With today’s technology changing and progressing to have greater intelligence, computing capabilities has changed. This has made way for the introduction of Automatic Dependent Surveillance – Broadcast (ADS-B) technology. This technology allows the data from the pilot deck to be shared with engineers on ground level. Since the rise in technology, NASA researchers developed a concept of operations for terminal-area precision spacing in 1999 (Koenke & Abramson, 2004).

Researchers in Europe have studied airborne precision spacing using a variety of different methods. They namely focused on time-delay algorithms in different operational conditions and measured the impact the new procedures on flight crew and air traffic control operations. With American and European research combined it has been proven that airborne-managed precision spacing is possible (Ivanescu, Powell, Shaw, Hoffman & Zeghal, 2004).The Advanced Air Transportation Technologies Project that’s run by NASA, formed an operationally viable approach to the spacing concept. This concept went through several name changes but finally agreed with Airborne Precision Spacing (APS). APS focus’s not just on pairing of aircrafts, but on spacing aircrafts in a stream on the tarmac. APS will always work to achieve the assigned goal at the runway threshold, not early or late. This allows for the spacing aircraft to clear out errored reactions far from the runway and only tightly manage the spacing where it is necessary (Grimaud, Hoffman, Rognin & Zeghal, 2005).

The first stage of development was called ‘ATAAS’. ATAAS uses time-history spacing between two aircrafts and concentrations on in-trail and final approach spacing. This is achieved by an extended Standard Terminal Arrival Route (STAR). The air traffic controller will clear the spacing aircraft when safe. The air traffic controller will then begin spacing relative to the assigned target aircraft as well as assigned spacing interval (Abbott, 2002). ATAAS was then developed to introduce the ability to merge traffic through different arrival routes. The calculations then changed from a time-history approach to a trajectory-based approach. The new spacing tool that in recent years has been created by NASA called the ‘AMSTAR’ can calculate the expected time of arrival for both the ownship and the leader. It can use the time difference as input to the speed control law, which is a law that remains unchanged. AMSTAR has had an upgrade in recent years, to improve the stability of the trajectory prediction and estimated time of arrival calculations. This way, the internal wind model can get real-time updates and to enable operations to start at cruise altitudes. Cruise altitudes enables for en-route merging and Continuous Descent Approaches (Weitz, Hurtado & Bussink, 2005).

A ‘Human-in-the-loop’ study was conducted at NASA’s Air Traffic Operations Laboratory (ATOL), this involved testing the merging and in-trail operations. Nine different aircrafts where studied at ATOL, where in which they would arrive at one of three different modeled airspaces. Sic of those nine aircrafts where flown by pilots, and three were flown by confederate pilots. The pilots could achieve a mean spacing deviation at the runway threshold of -0.8 seconds with standard deviation of 4.7 seconds. Several pilots made mistakes in vertical navigation modes and therefore had significant deviation from the reference vertical profile. Similar errors occurred during the same frequency in baseline runs. No significant difference was found in merging and in-trail operations, or between the different airspaces (Barmore, Abbott & Capron, 2005). Throughout research of APS, many extraneous variables, meaning interferences have been identified. These include limited surveillance range, wind forecasting accuracy, preconditioning of traffic before spacing operations start and the effects of having a range of final approach speeds (Lohr, Oseguera-Lohr, Abbott, Capron, Howell, 2005).

Future of airborne precision spacing It has been shown through simulations and commitment of research to flight testing, that Airborne Precision Spacing is able to achieve delivery to the aircraft runway threshold with high precision. With a standard error of only 1 second and a standard deviation of 2-3 seconds. Some studies and forms of research at NASA unfortunately have had confronting effects attributed to non-spacing aspects of the test. However, this is dependent on the influence the human in operation has on APS. Further testing with subject pilots would help to solidify this problem. In both the human-in-the-loop and fast-time simulations, there have been no signs that destabilizing effects the long string of spacing aircrafts. The testing of non-spacing aircrafts in the traffic flow has not yet been carried out, this could cause additional difficulties (Krishnamurthy, Bussink &Barmore 2004).

The spacing operations means that the pilot workload will only be mildly impacted. The Integration Flight Deck (IFD) and ATOL studies shows through subject questionnaires that pilots feel that an overall workload when spacing was not significantly different than the workload without spacing. Eye scan data was also collected during IFD tests and found that there was minimal change to the pilots scan pattern and dwell time when comparing spacing and non-spacing (Oseguera-Lohr &Nadler, 2004).

NASA views APS as one of the key specialty skills seen in safety in regards the Flight Management System. This flight management system would make room for capabilities of the aircraft to fly precise trajectories and to self-optimize under general constraints to become a useful resource when managing the changing demands on the air traffic system. In the future improvements that could be made is the ability to modify the planned route in real-time and continue to space along it. This would allow for the planned rout of both the lead aircraft and the ownship (Turkey, 1977).

Reference List

Barmore, B. (2006). Airborne Precision Spacing: A Trajectory-Based Approach to Improve Terminal Area Operations. Digital Avionics Systems Conference 2006, 25, pp.1-12.

I.Grimaud, E.Hoffman, L.Rognin, K. Zeghal, "Spacing Instructions in Approach Benefits and Limits From an Air Traffic controller Perspective", Proceedings of the 6th USA/Europe ATM Seminar at Baltimore, 2005.

T.S. Abbott, "Speed Control Law for Precision Terminal Area In-Trail Self Spacing" in NASA TM 2002-211742, Washington, DC, NASA, 2002.

D.H. Williams, "Time-Based Self-Spacing Techniques Using Cockpit Display of Traffic Information During Approach to Landing in a Terminal Area Vectoring Environment" in NASA TM-84601, Washington, DC, NASA, 1983.

E. Koenke, P. Abramson, "DAG-TM Concept Element 11 Terminal Arrival: Self Spacing for Merging and In-trail Separation" in Advanced Air Transportation Technologies Project, Washington, DC, NASA, 2004.

D. Ivanescu, D. Powell, C. Shaw, E. Hoffman, K. Zeghal, "Effect of Aircraft Self-Merging in Sequence on an Airborne Collision Avoidance System" in AIAA 2004-4994, Reston, VA, AIAA, 2004.

L. Weitz, J. E. Hurtado, F.J.L. Bussink, "2005 Increasing Runway Capacity for Continuous Descent Approaches through Airborne Precision Spacing" in AIAA 2005-6142, Reston, VA AIAA.

B. Barmore, T.S. Abbott, W.R. Capron, "Evaluation of Airborne Precision Spacing in a Human-in-the-Loop Experiment" in AIAA-2005-7402, Reston, VA, AIAA, 2005.

G.W. Lohr, R.M. Oseguera-Lohr, T.S. Abbott, W.R. Capron, C.T. Howell, "Airborne Evaluation and Demonstration of a Time-Based Airborne Inter-Arrival Spacing Tool" in NASA/TM-2005-213772, Washington, DC NASA, 2005.

R.M. Oseguera-Lohr, E.D. Nadler, "Effects of an Approach Spacing Flight Deck Tool on Pilot Eyescan NASA/TM-2004-212987" in, Washington, DC, NASA, 2004.

K. Krishnamurthy, F.J.L. Bussink, B. Barmore, "Fast-Time Evaluations of Airborne Merging and Spacing for Terminal Arrivals (AMSTAR)" in Advanced Air Transportation Technologies Project, Washington, DC, NASA, 2004

J. W. Tukey, "Explanatory Data Analysis" in, Reading, MA:Addison-Wesley, pp. 39-43, 1977.