Enroute Flight

User Preferred Routes

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 specific mission requirements.

Typically a UPR will be calculated by an aircraft operator’s flight dispatch based on factors such as forecasted winds, aircraft type and 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 published flexible 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.

Dynamic Airborne Reroute Procedures

Dynamic Airborne Reroute Procedures (DARP) refers to an oceanic in-flight procedure whereby the lateral profile of a flight can be modified periodically in order to take advantage atmospheric conditions of updated and updated forecasts. Typically, flight operators file flight plans some hours prior to a flight estimate 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 update profile is coordinated by the Airline Operations Center (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. A recent Air New Zealand analysis concluded that 58% of all flights from Auckland to North America assessed during the analysis sample would achieve fuel savings from the DARP procedure, resulting in an average fuel burn reduction of 453kg per flight, or roughly 1431kg of CO2 emissions.2

Flexible Track Systems

In an oceanic environment where the use of UPRs is not feasible, flexible track systems can provide an alternative 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 provide a generic optimised route between nominated city pairs.

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.

In a recent trial, 592 Emirates Airlines flights from Dubai to Melbourne and Sydney were selected to examine the benefits of the flexible track system.

For eastbound flights alone Emirates Airlines saved 628 tonnes of fuel and 57 hours in trip time. Analysing one recent flight from Dubai to Sydney, using this optimal air traffic management, Emirates Airlines saved 8040kg of fuel and 43 minutes of flight time. This equates to more than 6,800 kilograms of C02 saved. The average saving per flight was six minutes of flight time and one tonne of fuel.

Oceanic Separation Minima (50/50 & 30/30)

The capacity of oceanic airspace is severely constrained when legacy oceanic separation standards are in use.

Improvements in navigation capabilities have enabled reduction in the Oceanic separation minima to 50NM longitudinally and 50NM 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 30NM laterally.

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. This is due to the vastly increased access to optimum flight profiles associated with the tighter spacing of the aircraft. This enhanced efficiency is reflected in lower fuel burn and reduced emissions as more aircraft can fly closer to optimal tracks and altitudes.

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 increases airspace capacity and allows aircraft to fly closer to fuel efficient altitudes.

Cruise Climb (Block levels)

A cruise climb allows pilots to execute a gradual climb from one cruise altitude to another, which when properly configured enables the optimum altitude to be sustained for reduce fuel burn and emissions.

In circumstances where cruise climb is not permitted, block levels provide an efficient alternative. In a block level clearance a pilot is cleared to operate between two altitudes. As with the cruise climb the pilot is able to configure the aircraft for the optimum altitude to reduce fuel burn and emissions.

Time Based Arrivals Management

To reduce the environmental impact of delays caused by congestion at airports ANSP’s have introduced traffic flow management procedures and automated decision support automation to reduce the need for fuel techniques such as low altitude vectoring and aircraft holding, and improve fuel and emissions efficiency by shifting delays to the enroute phase of flight.


1 ISPACG/22 IP-16

2 Each minute of flying-time saved reduces fuel consumption by an average of 62 litres and reduces C02 emissions by 160 kilograms