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terms of gaseous emissions and noise, on airspace users in terms of fuel burn and on the
air transport system in terms of capacity utilisation.
7.3.18 Care should be taken to avoid that fuel savings made in one flight phase are offset by
increased fuel burn in another phase. Figure 96 outlines some of the issues that need to be
considered.
ATFM ground holding
Keeping the aircraft on the ground is not always the most fuel efficient strategy. It
can be more fuel efficient to let the aircraft fly at reduced speed. The amount of time
that can be absorbed in this way is however limited.
With the current ICAO “first come first served” rule, ATFM delays can
paradoxically even lead to a higher overall fuel burn as pilots fly at higher speed to
recover part of the ATFM delay en-route only to join the arrival queue at the airport
of arrival.
PRR 2009 81 Chapter 7: Environment
Speed adjustments
The reduction of speed already in the en-route phase is more fuel efficient than
airborne holdings or path stretching and arrival sequencing should be achieved to the
extent possible through speed adjustments en-route.
Due to the narrow speed envelop in cruise, any speed reduction (to fuel optimum
speed) has to start early enough. Efficient management of the flight trajectory
therefore require co-ordination across ATC units and in many cases across different
ANSPs. The amount of time that can be absorbed in this way is however limited.
Airborne holdings
Optimum holding levels vary considerably by aircraft type. For many aircraft types
(e.g. A300 A330-203, A310-324) it is more efficient to hold at FL100 than at FL
350. As a result, for a number of aircraft types where a holding requirement is
transferred to the en-route phase in order to support a continuous descent (CD), if not
properly managed, could even result in a higher fuel burn than if the CD operation
had not been attempted.
Figure 96: Considerations for optimising the arrival flow
7.3.19 The current operational ATM concept
in Europe is fragmented and the focus is
on the management of departure times.
When traffic is anticipated to exceed the
available capacity en-route route or at
airports, aircraft are held at the
departure airports through the
application of ATFM departure slots to
limit airborne holding (and fuel burn) at
the arrival airports (see Figure 97).
additional fuel burn
due to increased speed to
recover delay & to join arrival
queue
Ground holding
at departure
Airborne holding
Unconstrained & path stretching
Figure 97: ATM concept today
7.3.20 A more integrated approach focusing on
optimising the four dimensional (4-D)
trajectory of flights in order to minimise
fuel burn (and emissions) while
maximising the utilisation of available
en-route and airport capacity should be
facilitated.
7.3.21 The integrated approach would combine
flow management techniques to reduce
fuel burn but requires a well designed
set of tools and procedures.
Limited ground
holding
Optimised
descend
Speed
adjustments
fuel saving
due to reduced speed
already in the en-route phase
Figure 98: Integrated trajectory
management
7.3.22 In the short term priority should be given in the implementation of arrival managers at
main airports as required by DMEAN and SESAR IP1. While arrival managers have been
in place for many years at some airports (COMPASS at Frankfurt, MAESTRO at Paris)
they may not yet be fully utilised for the purpose envisaged and are still not available at
many airports. When fully utilised, arrival managers will help to improve fuel efficiency
in two complementary ways:
Firstly by optimising the arrival sequence at the runway and therefore by optimising
the arrival throughput; and,
Secondly by moving part of the sequencing en-route and thus reducing the need to
vector arriving aircraft which in turn facilitates Continuous Descent Operations
(CDO) without the need to absorb delay in other parts of the flight.
PRR 2009 82 Chapter 7: Environment
7.3.23 In the longer term (SESAR) the focus should
move from operations based on accurate
departure times (current ATFM concept) to a
concept that focused on the required time of
arrival. This would make better use of the
Required Time of Arrival (RTA) functionality
available on many aircraft today.
7.3.24 Moving towards a requested time of arrival
concept needs an increased predictability of
capacity variations (and therefore better
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Performance Review Report 2009(60)
