Introduction of RVSM on a Trial Basis in the North Atlantic Region

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Introduction of RVSM on a Trial Basis in the North Atlantic Region

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

WP No. 83

Introduction of RVSM on a Trial Basis in the North Atlantic Region


Following the introduction of RVSM on a trial basis in the North Atlantic region from the 27th March 1997 and the proposed introduction on a trial basis within the ECAC region of European Airspace from November 2000 , the time has come for IFATCA to review policy in a global context rather than by regions as hithertofore.

The policy adopted by conference previously together with the outcome from the European Regional Meeting 1997 needs to be updated and formulated in Global terms for the future guidance of our Federation.


In the mid 1970’s a series of fuel shortages and the resultant rapid escalation of fuel costs, together with a demand for more efficient use of available airspace prompted the need for an examination of the feasibility of reducing the vertical separation above FL290 from 2000ft (600m) to 1000ft (300m).

In 1980 at RGCSP/4 the ICAO Review of the General Concept of Separation Panel concluded that despite cost and time involved the potential benefits were so great that states should be encouraged to conduct the major evaluations necessary. 1982 – co-ordinated by RGCSP States initiated programmes to comprehensively study the question of reducing the VSM above FL290. Canada, Japan, France, the former Federal republic of Germany, Kingdom of the Netherlands, the United Kingdom, the former Union of Soviet Socialist Republics and USA carried out studies. In December 1988 the results were presented at RGCSP/6. The studies employed quantitative methods of risk assessment to support operational decisions concerning the feasibility of reducing the VSM. Risk assessment had two elements:

  1. Risk estimation which concerns the development and use of methods and techniques with which the actual level of risk of an activity can be estimated;
  2. Risk evaluation which concerns the level of risk considered to the maximum tolerable value for a safe system. The level of risk deemed acceptable is termed the target level of safety (TLS).

The basis of the process of risk estimation was the determination of the accuracy of height keeping performance of the aircraft operating at/above FL290. This was achieved through the use of high precision radar’s to determine the actual geometric height of aircraft in straight and level flight . This was compared to the geometric height of the flight level to which the aircraft had been assigned in order to determine the total vertical error (TVE) of the aircraft in question. With this information it was possible to estimate the risk of collision solely as a consequence of vertical navigation errors of aircraft to which procedural vertical separation had been applied. Similarly, the RGCSP assessment TLS was derived to apply to this contribution to collision risks only- it did not encompass the contributions from other sources of vertical collision risk like emergency descents or human error.

The recognition of the fact that there were several sources of vertical risk in addition to vertical navigational errors played a role in the choice of TLS values by States during their studies. Derived values for TLS ranged between 1×10 to the power of minus 8 and 1×10 to the power of minus 9 fatal accidents per flight hour. On the basis of these figures the RGCSP employed an assessment TLS of 2.5×10 to the power of minus 9 fatal accidents per flight hour to assess the technical feasibility of a 1000ft. VSM above FL290 and also for developing aircraft height keeping capability requirements for operating 1000ft VSM RGCSP/6 concluded that 1000ft VSM was technically feasible. In reaching its conclusion the panel found it necessary to establish:

  1. Airworthiness performance requirements embodied in a comprehensive MASPS for all aircraft utilising the reduced separation;
  2. New operational procedure;
  3. A comprehensive means of monitoring the safe operation of the system.

RGCSP/7 (November 1990) completed the global guidance material for the implementation of the 1000ft. RVSM. Main purpose was to provide regional planning groups with the basis for development of documents , procedures and programmes to enable the introduction of the RVSM within their particular regions in accordance with the criteria , requirements and methodology outlined in the report of RGCSP/6 (Doc. 9536). The panel noted that further detailed work by RPG’s would be required to establish the conditions for the implementation of RVSM in each region individually and that any necessary amendments to the Regional Supplementary Procedures (Doc 7030) should be developed by the RGP concerned.

In parallel with the work of RGCSP the NAT SPG ( North Atlantic Systems Planning Group) initiated studies in May 1990 (NAT SPG/26) to examine the application of the RVSM in the NAT Region. NAT SPG/27 incorporated the RVSM concept in the NAT future concept description and in the NAT Implementation Document (NAT ID). It established a Vertical separation implementation group (VSIG) to prepare for NAT SPG/28 for May1992. At NAT SPG/29 -the VSIG was subsumed into the Reduced Separations Standards Implementation Group (RSSIG).

A decision on the implementation and operation of a 1000ft. vertical separation minima with MNPS airspace of the NAT Region was made in 1992. MNPS airspace is defined as being that portion of the NAT Region airspace extending between latitude 27 North and the North Pole , bounded in the East by the Eastern boundaries of the control centres (CTA) Santa Maria Oceanic , Shanwick Oceanic and Reykjavik and in the West by the Western boundary of New York Oceanic excluding the area west of 60deg west and south of 38deg 30min North (ICAO Doc 7030 Regional Supplementary Procedures- NAT Part 1)

In order to obtain maximum benefit from the implementation of the full range of RVSM (FL290 to FL410 inclusive), the vertical dimensions of MNPS Airspace will extend from a floor of FL285 to a ceiling of FL420 when RVSM is implemented in the NAT MNPS Airspace.

During the NAT verification phase each aircraft group of each NAT operator underwent verification of height keeping performance accomplished by carriage of a Global Positioning System (GPS) Monitoring Unit (GMU) or by overflying a H eight Monitoring Unit (HMU)- although GMU carriage or HMU overflight did not necessary have to be made on a NAT flight , it had to be carried out in level flight between FL290 and FL410.

Trial Phase will be used to confirm and then to build statistical confidence that the risk in the system is at or below the TLS and to assess whether it will remain so taking into account increases in traffic and improvements in lateral navigation performance.

ICAO NAT Doc 002- Guidance Material on the Implementation of a 300m (1000ft) Vertical Separation Minima in the North Atlantic Region (1st Ed. July 1994). Part 6 gives material with the purpose of giving the pilot and the Air Traffic controller guidance on actions to take under conditions of equipment failure and encounters with turbulence.

Results of trials to be inserted when available for first six months March – September 97

In the European context it is proposed to introduce RVSM not in the ICAO European Region (EUR) but in the ECAC States on an Operational Evaluation Phase from November 2000 and from November 2001 for its full Implementation. Within the ECAC Area the safe and efficient introduction of RVSM requires a number of ATC Support Functions to be implemented at the start of RVSM Operational Evaluation Phase:

  1. Aircraft Equipage: all aircraft except state aircraft will be required to be “RVSM approved” in order to operate within the RVSM Airspace. (ICAO definition of State Aircraft “Aircraft used in military, customs and police services”) Eurocontrol will urge states to adapt their state aircraft operating as General Air Traffic (GAT) to the level of MASPS compliance to the extent possible.
  2. Minimum Separation: required in RVSM Airspace will be:

a) 1000ft between aircraft RVSM approved;

b) 2000ft between a non approved and an RVSM approved aircraft;

c) 2000ft between two aircraft neither of which is RVSM approved.

Two major safety considerations of a very high order have been carefully assessed:

  1. ATC will be obliged to apply a distinct vertical separation minima within the RVSM airspace according to the aircraft’s RVSM approved status;
  2. ATC must ensure that non-RVSM approved aircraft ,other than state aircraft are not inadvertently cleared into RVSM Airspace.

An accurate, timely and unambiguous display of this information to the controller is necessary to ensure the safe handling of this mix of aircraft inside the Flight Level Band s FL290-410.

Flight Planning Provisions

It is proposed that information regarding:

(1) Type of Flight (State/non State) will appear in ICAO FPL: Field 8

(2) RVSM approved status: Field 10

(3) Requested FL: Field 5

(4) Other request for special handling: Field 18

The IFPS (Integrated Initial Flight Plan Processing System) will need to process such information for distribution to the individual FDPS’S of the ACC’s of the ECAC area.

Operational Requirements

(1)  ATC must have a means of readily identifying when to apply 2000ft vertical separation.

(2)  ATC must have a means of readily identifying State aircraft non-RVSM approved.

The following operational features are required ATC support functions :

(3)  RADAR ENVIRONMENT; position symbols and/or labels of State non-RVSM approved, operating as GAT within RVSM airspace Shall have clear distinguishable features different from the position symbols of RVSM approved aircraft. The means by which it is applied to the Radar position symbol and /or label of the aircraft concerned shall be automatic with the required data extracted from the FDPS. Where the system cannot ensure this a manual intervention shall be necessary;

(4)  Information regarding a State or Civil aircraft’s non-RVSM compliance Shall be displayed on flight strip (paper or electronic);

(5)  Indication that a State aircraft, non RVSM approved is a “State” aircraft Shall be displayed on flight progress strip(paper or electronic);

(6)  Short Term Conflict Alert and Medium Term Conflict Detection Tools:

(1)  STCA and MTCD systems in ACC’s applying RVSM shall be able to assess a VSM of 1000Ft up to and including FL410.

(2)  STCA and MTCD systems in ACC’s applying RVSM should be able to assess the selective application of a VSM of 1000FT or 2000FT as determined by the approval or non-approval status of the aircraft concerned.

The following additional features are highly desirable :

(1)  Where radar is used as the primary tool for applying separation, above or below RVSM airspace according to the operational requirements of each ACC, the radar position symbols and/or radar labels of both State Aircraft, non RVSM approved operating as GAT and civil non State aircraft non-RVSM approved should have clear distinguishable features different from the radar symbols and/ or radar labels of RVSM approved aircraft.

(2)  In addition to Flight Plan Data distributed by IFPS, OLDI should support the transfer of information related to requests for special handling in the RVSM airspace contained in Field 18 of ICAO Flight Plan.

The ANT grouping have drawn up “ATC Procedures required for the Implementation of RVSM” taking into account the results of simulations sponsored by Eurocontrol namely-

(1)  The second continental RVSM Simulation _ S04

(2)  Real Time RVSM Simulation Study – Nieuw Millligen, The Netherlands

(3)  Third Continental RVSM Simulation – S08

The procedures cover :

(a) General Procedures

(b) Non-RVSM approved State aircraft operating as GAT

(c) State Aircraft operating as OAT within RVSM Airspace

(d) Airspace Restrictions and reservations

(e) Flight Planning

(f) Inter-centre co-ordination

(g) Contingency Procedures Comms. Failure/Emergency Descents

(h) Transition Procedures

(i) Phraseology

Major difference between NAT RVSM and Continental ECAC RVSM

Generally the NAT flow is unidirectional i.e. either East/West or West/East and level flight while Continental traffic is multidirectional with high proportion of climbs/descents giving totally different complexities.

In the simulations carried out in Europe there was a failure in determining any clear advantage for either the single or double FLOS but a decision has been adopted to commence the trials/evaluations using the single alternate – maintaining the status quo as pertained to airspace below FL290 of odd and even levels.

Current Policy

The current policy derives from conference working papers 90/B4/WP50 and 96/B3/WP115. It states:

“The reduction of vertical separation above FL 290 should not be implemented in any Region until the necessary procedures, staff and equipment are available to safely and expeditiously handle aircraft in the airspace experiencing the reduction and also in systems responsible for transition areas to airspace not affected by a reduction.

Only aircraft capable of meeting the Minimum Aircraft Systems Performance Specifications upon which reduced separation is dependent be permitted to operate in areas where reduced vertical separation is in effect. Exceptionally, State aircraft may be accepted when appropriate procedures have been evaluated, validated and ATCO’s are trained in the operation of a mixed traffic environment.”

Single or Double Alternate FLOS

Following the simulations in Europe and no clear preference for either system being available IFATCA representative looked for direction from European MA’s at the European Regional Meeting October 1997 as to what should be supported.

After protracted discussions the following was accepted by the majority of MA’s with the exception of two as Provisional Policy:

“Failing a clear operational advantage for either the single or double alternate FLOS, IFATCA Europe proposes that the RVSM trials utilise the single alternate FLOS in order to achieve the global application in accordance with ICAO Annex 2. In order to validate the results during this trial period , enhancements on a sub-regional level may become necessary through adequate FLAS.

IFATCA Europe is concerned about the actual state of preparations regarding the introduction of RVSM in the ECAC area planned for trials in November 2000.

IFATCA Europe urges all states concerned to ensure that the appropriate infra- structure will be in place prior to the commencement of these trials ,this involves staff, equipment, training airspace and route structure, including the transition areas. All factors must be verified and validated through simulations prior to implementation.

IFATCA Europe insists that the number of non-MASPS State aircraft, entering the RVSM airspace, be kept to the absolute minimum.”

To Conclude

The IFATCA Policy should consider what preference it supports in relation to the application of a single or double alternate FLOS in the interest of providing an eventual global seamless system.

IFATCA Europe has accepted as provisional policy the use of the single alternate FLOS in a portion of its region. Conference must decide whether to endorse this provisional policy amended for global application.

Last Update: September 28, 2020  

March 5, 2020   863   Jean-Francois Lepage    1998    

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