Enroute & Oceanic Flight
User Preferred Routes (UPRs)
A User Preferred Route (UPR) during the oceanic phase of flight is defined as a lateral profile developed for each individual flight by the flight operator. These lateral profiles are customised in order to meet the specific needs of the aircraft operator for that flight, such as fuel optimisation, cost-index performance, or military mission requirements.
Typically a UPR will be calculated by an aircraft operator's flight dispatch based on factors such as forecasted winds, type aircraft and aircraft performance, convective weather and scheduling requirements.
UPRs are a favoured enhancement to oceanic operations where air traffic control (ATC) limitations previously required that aircraft fly on fixed air traffic services (ATS) routes, or flexible published track systems. This enhancement is directly attributable to the implementation of ground and airborne improvements such as automated conflict prediction, conformance monitoring, and automatic dependent surveillance (ADS).
When UPRs are created based on fuel optimisation considerations, the corresponding savings in greenhouse gas emissions can be substantial.
UPRs are often constrained by requirements for flights to cross boundaries between Flight information regions at predetermined points. This can be alleviated through improved ground-ground integration. Fore example through the implementation of ATS interfacility data communication (AIDC)
A key enabler for the implementation of UPRs is the implementation of Air-Ground Datalink Communications.
Dynamic Airborne Reroute Procedures (DARP)
Dynamic Airborne Reroute Procedures (DARP) refers to an oceanic in-flight procedure to periodically modify the lateral profile of a flight in order to take advantage of updated atmospheric conditions and updated forecasts. Typically, flight operators file flight plans some hours prior to a flight's estimated time of departure. Often, revised upper wind forecasts are available after the flight plan is filed or the aircraft departs.
DARP allows aircraft operators to calculate revised profiles from the aircraft's present position to any subsequent point in the cleared route of flight in order to realise savings in fuel or time. This updated profile is coordinated by the Airline Operations Centre (AOC) with the flight crew, and sent to ATC as a reroute request from the aircraft.
Initially demonstrated in the South Pacific in 1999, recent enhancements to conflict prediction, conformance monitoring and inter-facility coordination in Air Traffic Management automation systems have enabled the wider implementation of the DARP. Participating ANSPs can accommodate multiple in-flight reroute requests across airspace boundaries.
The DARP can provide significant savings in fuel and emissions.
Flexible Track Systems
In circumstances where fixed routes are in use and the implementation of UPRs in continental airspace is not practicable in the medium term, flexible track systems can be considered as an interim best practice as they are vastly more efficient than fixed ATS routes.
A flexible track is typically calculated so that all flights flying a specific city-pair route will utilise a single lateral profile or track. This track is calculated based on forecasted meteorological data and a representative aircraft performance model and published via NOTAM. A flexible track system is a series of flexible tracks designed to be laterally separated from one another to accommodate high traffic density.
Flexible tracks provide greater efficiencies than fixed ATS routes, because they are optimised to take advantage of favourable winds. Flexible tracks do not provide the same level of efficiencies to individual aircraft that can be achieved in a UPR system. However in circumstances where implementation of UPRs is not yet feasible a flexible track system provides a notable improvement in efficiency and reduction in emissions.
Reduced Separation Minima
Reduced separation minima allow more aircraft access to optimum routings and altitudes; the enhanced efficiencies of optimum routes and altitudes can result in lower fuel burn and reduced emissions. This enhanced efficiency is reflected in lower fuel burn and reduced emissions as more aircraft can fly closer to optimal tracks and altitudes.
Direct surveillance in remote areas
Within the Asia Pacific area there are a number of regions which have been treated as remote airspace and subject to large horizontal separation minima, but lend themselves to the introduction of direct surveillance systems such as ADS-B.
The introduction of direct surveillance into these areas can provide an environmental benefit if reduced separation minima are also implemented.
Oceanic Separation Minima
Improvements in navigation capabilities have enabled reduction in the Oceanic separation minima to 50NM longitudinally and laterally. When coupled with direct controller pilot communications via data-link and automatic dependent surveillance, aircraft meeting certain navigation performance requirements can be safely separated at as little as 30NM longitudinally and laterally. In late 2014 a further reduction to 20NM longitudinally and laterally is expected.
The reduced separation minima for use in the oceanic environment are published in the ICAO Procedures for Air Navigation Services – Air Traffic Management (Doc 4444) and the ICAO Annex 11 - Air Traffic Services.
Qualified aircraft navigating in airspace where these reduced separation minima have been implemented achieve significantly greater efficiencies than aircraft that cannot meet these standards.
Reduced Vertical Separation Minima (RVSM)
Improvements in vertical height keeping and altimetry in the modern fleet of aircraft, coupled with new procedures and monitoring requirements has allowed a reduction of vertical separation between aircraft operating above FL290. This standard, known as Reduced Vertical Separation Minimum (RVSM), allows the vertical spacing of qualified aircraft to be reduced from 2000ft to 1000ft in airspace where the standard has been implemented.
Oceanic RVSM allows aircraft to fly closer to fuel efficient altitudes, and execute smaller step climbs, which require less fuel.
Time Based Arrivals Management
To reduce the environmental impact of delays caused by the demand placed on airports ANSPs have introduced traffic flow management procedures and automated decision support automation to reduce arrivals congestion into high density airspace and improve fuel and emissions efficiency by shifting delays to the less congested en- route phase of flight.
These systems provide controllers with sequencing information, including times at strategic arrival points that the controllers may use to meter aircraft. Effective time-based arrivals management reduces low altitude vectoring and arrivals holding while also improving merging and spacing of arriving aircraft to maximize airspace efficiency.