North Atlantic traffic streams
The major traffic flow between Europe and North America takes place in two distinct
traffic flows during each 24-hour period due to passenger preference, time zone
differences and the imposition of night-time noise curfews at the major airports. The
majority of the Westbound flow leaves European airports in the late morning to early
afternoon and arrives at Eastern North American coastal airports typically some 2
hours later - local time - given the time difference. The majority of the Eastbound
flow leaves North American airports in mid/late evening and arriving in Europe early
to mid morning - local time. Consequently, the diurnal distribution of this traffic, has
a distinctive tidal pattern characterised by two peaks passing 30° W - the Eastbound
centred on 0400 Universal Co-ordinated Time (UTC) and the Westbound centred on
1500 UTC.
Baseline forecasts for 2015 show a 71 % increase of traffic compared to 1996, while
optimistic figures show 96% increase (almost double).
The current North Atlantic tracks
There are three types of tracks above the North Atlantic Ocean:
1. Tracks in the Organised Track System (OTS),
2. Fixed Tracks,
3. Random tracks.
The OTS is set up on a diurnal basis to facilitate a high throughput of traffic by
ensuring separation for the entire oceanic crossing. Each core OTS is comprised of a
set, typically 4 to 7, of parallel or nearly parallel tracks, positioned in the light of the
prevailing winds to suit the traffic flying between Europe and North America.
Examples are shown in Figure 1 and 2. Longitudinal separation between in-trail
aircraft using the Mach Number Technique is 10 minutes and aircraft which satisfy
MNPS are separated laterally by a minimum of 60 NM. Re-clearances for change
tracks are normally limited to the provision of some step climbs and/or re-routes.
Figure 1: Example of a Day-Time, Westbound Oceanic Track System, Reference [1]
Figure 2: Westbound tracks, Reference [2]
Operators may also choose to flight plan random routes. However, random traffic
competes for routes and flight levels on a first-come, first-served basis and aircraft
flying random routes conflicting with the OTS are likely to be subject to flight level
or routing restrictions. - unless the track is above or below the system. Aircraft
electing to fly random tracks are required to flight plan on great circle tracks joining
successive significant points defined by whole degrees of latitude intersecting
meridians spaced by 10 degrees of longitude (20 degrees North of 70 degrees N).
Shortcomings of the current North Atlantic system
The North Atlantic System has a series of existing shortcomings, as identified by the
North Atlantic Systems Planning Group, working on behalf of the International Civil
Aviation Organisation (ICAO) Error! Reference source not found.. These
shortcomings are identified to be structural, that is, inherent to the system itself and
make that the users currently do not enjoy maximum economy in their operations with
minimum restrictions.
The existence of a track structure brings in rigidity, making the traffic flow over the
Atlantic not efficient. As the variability of the wind patterns is higher than the
variability of the OTS ammulgation, the system is penalising in terms of flight time
and consequent fuel usage. Inaccuracies in the meteorological forecast may cause the
operator to choose a track which does not make optimal use of prevailing conditions,
which plays an important role in flight economics. In addition, the limitations of
turbulence forecasting may operationally impact upon the application of RVSM levels
for OTS and random flights resulting in reduced capacity and efficiency.
Besides the OTS system inevitably limits users to choose preferred cruise parameters
as flight level and Mach number. Cruise climbs and tracks changes are possible
during a crossing, but not always and certainly not real-time.
Furthermore, the surveillance and communication systems limit the ATC capabilities
in the Atlantic region. Manual waypoint insertion errors for example can cause Gross
Navigational Errors and the current surveillance system provides only a limited ability
to detect those errors and to contain them by ATC intervention. The ATC limitations
dictate relatively large separation minima and this in turn limits exploitation of the
airspace capacity. The inability in certain areas to apply RVSM reduces system
capacity further. While the North Atlantic Region as a whole is not saturated, a
capacity shortfall can occur in the busiest part of the Europe/North America axis. This
further constraints on aircraft profiles: aircraft may not obtain the desired route or
flight level and therefore must be re-cleared on a less optimal flight profile.
In areas outside the OTS, some tactical flexibility is achieved, particularly where
traffic operates on random routes. An efficient use of such tactical control is however
again limited by present communication and surveillance systems.
A significant problem for the introduction of new ATM concepts, such as “Free
Flight”, is that the main stakeholders in the ATM system, the airlines, require a quick
return on their investments. Another problem for the introduction of “Free Flight” is
the difficult transition path from today’s Core-European or US domestic ATM system
to a new ATM system incorporating “Free Flight”. For this reason, a way to introduce
“Free Flight” was figured out, while still meeting the short term, return on investment
requirements of the airlines and the requirement for a smooth transition path. The
solution is called: “North Atlantic Free Flight”.
NLR, in the ASSTAR (Avanced Safe Separation Technologies and AlgoRithms)
project is heavily involved in this “North Atlantic Free Flight” concept, which forms
part of ASAS Package II. This ASAS application will be assed on the Eastbound
traffic flow, see figure 3
ASSTAR aims to improve management of domestic/oceanic interface and facilitate
flow management where required, without compromising operational safety levels.
ASSTAR is a Eropean Union co-funded project which started in January 2005.
Figure 3: Eastbound track
ASSTAR will perform research into the operational and safety aspects of the ASAS
Package II type applications indicated below in order to realise the significant
potential benefit to the user community in the 2010 plus time frame:
 Delegation of conflict resolution manoeuvres to the air in radar controlled
airspace, i.e. crossing and passing.
 Reduced controller workload and improved flight efficiency is expected
 Use of ADS-B to support new operations in oceanic and other non-radar
airspace, enabling more optimal routing, including enhanced use of wind
corridors and passing and level changing
 Improvements to flight path efficiency currently restricted due to the
procedural separation standards
Research objectives include:
 ASAS manoeuvre design, simulation and evaluation
 Definition of supporting procedures
 Air & Ground installation & implementation issues
 Benefits
 Safety assessment
 Impact on Regulations
References
Reference [1] : “Guidance and Information Material Concerning Air Navigation in
the North Atlantic Region”, Seventh Edition, January 2002, Prepared by the ICAO
European and North Atlantic Office, NAT DOC 001.
Reference [2]: http://www.bcavirtual.com/crossing_the_north_atlantic.htm)