37TH ANNUAL CONFERENCE, Toulouse, France, 30 March – 3 April 1998

WP No. 107



Approximately 9 years ago the NATSPG tasked itself to improve the utilisation of airspace within the North Atlantic and find a suitable route ahead for reduction of separation standards.

The group came up with the initial idea of , once MNPS had been “bedded in” and was acceptable to all ATC agencies and users, a reduction of the Vertical Separation Minima would occur.

This they confirmed would be an initial step on the long road to Free Flight.

So, on the 27th March 1997, Phase 1 of RVSM commenced, utilising the levels 330, 340, 350, 360 and 370.

The Problem

To enable aircraft to utilise RVSM levels the operators had to ensure that they were Minimum Aircraft System Performance Specification (MASPS) approved. This approval would in turn allowed the operators the right to flight plan and fly within RVSM airspace.

Another major benefit for the users would be the reduction of area taken up by the Organised Track System on the North Atlantic. This basically meant that there would be more area available for flying random routes outside the track system whilst within the OTS the number of flight profiles nearer the required Minimum Time track would also increase.

RVSM operations had Condensed the size of the core of traffic by enabling more aircraft to fly within a smaller area.

Unfortunately the commencement of RVSM OPS brought to ahead a problem which had been with us for a long time, Turbulence or to be more specific Wake Turbulence.

Together with TCAS Nuisance TA’s , Wake Turbulence has become an integral part of NAT library of problems.

This significant increase in density of traffic also meant that during aircraft emergencies or during contingency operations within the OTS, crews would be encountering for more aircraft than was previously seen.

The main reason for this is the fact , that due to the standard of aircraft navigational systems, all aircraft within the NAT OTS are flying from one point e.g. 55N 010W to the next e.g. 55N 020W extremely accurately. They are being piled one on top of another with only 1000ft between them. No wonder the crews are subject to nuisance TA’s and Wake Turbulence.

Possible Solution

What is needed to resolve this predicament is better utilisation of the minimum lateral separation, 60 miles.

If this separation was reduced to 50 miles an airway could be established for each organised track instead of a straight line.

This airway would be 10 miles wide ( 5 miles either side of track centerline) thus enabling aircraft to be spread out yet still on the minimum timetrack.

It would also enable aircraft at set levels e.g. 310, 330 etc to fly left of centerline whilst FL 320, 340 etc flew right of the centerline. This would immediately reduce the physical density of aircraft on tracks.

Another tool available for the reduction of traffic density within the OTS would be the omission of a Safety Flight Level (s) on the published tracks.

This level (or levels) could provide a safe haven for aircraft during periods of emergency whilst not reducing the advantages for users of RVSM.

The two levels initially suggested were FL 300 and FL 400 ( easy to remember)

The omitting of such levels, incorporated with the establishment of airways, would I believe drastically reduce the occurrences of wake turbulence and nuisance TA’s on the North Atlantic. If these measures were in place by the time Full RVSM was commenced it would ensure that the North Atlantic continued to be area where safety and traffic awareness was paramount.

Last Update: September 28, 2020  

March 10, 2020   503   Jean-Francois Lepage    1998    

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