Trajectory-Based Operations (TBO) - Joint Planning and ...

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Trajectory-Based Operations (TBO) Study Team Report • Loss of three-mile separation using ADS-B, since the GNSS is the source of broadcast surveillance, requiring reversion to the equivalent of radar separation • Loss of functions enabled by TBO, like self separation, paired approaches, and airborne merging and spacing, since aircraft could not “see” each other • Loss of VCSPR operations • Loss of low-visibility surface operations between 300 and 1,200 RVR • Degradation of oceanic and off-shore separation as inertial systems begin to lose precision, requiring procedural measures to begin diverging aircraft and using vertical separation and speed control in the interference area • Oceanic and off-shore operations by aircraft not carrying an inertial system where dual GNSS without inertial is an accepted equipment installation for oceanic and remote areas (FAA Order 8400.12A and 8400.33) • Diversity of departure paths dependent on lower RNP values would be reduced to support larger separations • Some aircraft lose conflict-free 4DT because they lack a source of position and navigation capable of supporting RNAV The duration and size of the interference area determines the impact of an interference event. The time to replace the signal in space dictates a large-scale system failure impact. As an example, it is reasonable to assume a 300 nm radius area of interference in oceanic airspace (the point source may be a ship on the surface) 22 . Flying through the widest part of the interference would take approximately 100 minutes before GNSS coverage would be restored. In that same 100 minutes, the inertial reference unit will have lost 13 nm of precision. 23 If the aircraft takes its output for ADS-B from the navigation bus, then other aircraft that had ADS-B In would still be able to see the aircraft. However, if GNSS were the only source of ADS-B, the aircraft would now only be seen on TCAS. Likewise, the worst case is for those aircraft flying with dual GNSS receivers and no inertial that would now be without navigation signals and have to rely on dead reckoning, especially in airspace that has no surveillance coverage from radar. Within TBO airspace, quick identification by the ANSP of the extent of the interference area by mapping ADS-B position reports (there before, not there now) will provide a plot that can then be used to re-route traffic. Once mapped, the area becomes the equivalent of a weather event and aircraft are handled accordingly to route around the interference. Those that are trapped in the interference are now dependent on a backup. Most air carrier aircraft will still have DME-DME updates supporting the FMS, and will continue under TBO with some separation changes needed. Those aircraft not able to derive their own position will require vectoring until clear of the interference area. While this approach will work in the case of interference, it is of little use with a system failure of GNSS itself, where the coverage area could be quite large. A likely scenario for disruption of flight operations is a localized intermittent, mobile interference source. The scenario is based on the greatest possible disruption in a major metropolitan area, and 22 300 nm diameter distance is used here based on DOD point interference experience for testing interference. 23 AC 90-100A U.S. Terminal and En Route Area Navigation (RNAV) Operations specifies no greater than two nm/15 minute interval of no update to the IRU. Joint Planning and Development Office 73
Trajectory-Based Operations (TBO) Study Team Report relies on disruption of operations to gain publicity. Most air carrier and large business aircraft could continue to dispatch using inertial navigation and flying out of the interference area. No very-light jets and smaller business aircraft carry inertial systems and would be dependent on a VFR departure only. Most arrivals would continue, but the question is whether or not the vectoring workload would be too great. Today, radar vectors manage the majority of arriving traffic at a major airport. In 2025, traffic densities would nearly double, making radar vectors a fallback in the absence of any other alternative PNT questionable because of controller workload. It is likely that demand would need to be cut back to approximately half for air traffic controllers to handle a busy airport. The continuing intermittent disruption of PNT raises the need to identify the maximum traffic density that could be handled by radar vectors as a backup to GNSS and whether there is an alternative PNT strategy that could continue to support TBO in the presence of GNSS interference or system failure. 16.4 Security Incident An aircraft is deviating from its 4DT and not responding to communications. Alerts from conformance monitoring have already sounded and the aircraft is being tracked with ADS-B, secondary, and primary radar. Its destination and intentions are a mystery for the Department of Defense (DOD) and the Department of Homeland Security (DHS). The ANSP’s job is to clear out airspace by modifying the 4DTs of other aircraft. Some of this will be through the use of closed trajectories; others will be open trajectory vectoring as control by exception. The situation is quite fluid, but simulations and drills have established the boundaries of a new flight corridor for our deviating aircraft. As its flight track changes, a buffer is established that will be treated by the ANSP TBO evaluation service and distributed through network-centric operations. While the concept of clearing the airspace is likely, the threat scenarios are highly variable. This aircraft could have been in en route cruise, or could have just taken off. Time and location of detection of the deviation plays a central role in the ANSP-required actions. What TBO brings to the table is the continuous nature of conformance monitoring. Parameters can be built into the conformance monitoring module to detect more than just a deviation from flight track. Speed changes, altitude deviations, missed turn points, and erratic changes within the boundary of RNP performance can all be detected and used as an early indicator of problems. Time is lost in assuming that the aircraft has some other reason for deviating. By setting performance parameters on conformance and linking this action to net-centric operations, common situational awareness allows for earlier detection of rogue action. AOCs are alerted to the event and the nature of incident. The AOC can verify intent and provide necessary information to DHS and DOD. The ANSP’s TBO evaluation service begins to build a moving temporary flight restriction (TFR) around the deviating aircraft against criteria that are preestablished and based on speed and altitude. 16.5 Regulating Demand Off-nominal operations require balancing demand with the capacity for conditions. The challenge is to regulate demand only to the extent that it is needed to manage the throughput. A significant increase in capacity (less demand constraint) will be realized just by shared situational awareness and the use of network-centric operations to exchange information and strategically manage an event. This transparency of actions helps to make control measures more realistic for the situation and removes Joint Planning and Development Office 74
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