Documented Evidence from both IFALPA and IFATCA

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Documented Evidence from both IFALPA and IFATCA

38TH ANNUAL CONFERENCE, Santiago, Chile, 15-19 March 1999

WP No. 92

Documented Evidence from both IFALPA and IFATCA


Documented evidence from both IFALPA and IFATCA suggest that the FANS-1/A data link system has a number of significant deficiencies. These problems stem from various causes, some technical, some procedural, some related to the Human Machine Interface (HMI), and some related to user training and currency.

A survey of air safety incident reports submitted in relation to a currently operating oceanic control system utilising FANS1/A reveals no incidents relating to loss of separation but reports frequently unreliable datalink communications. There are references to several network outages with no advance notice of the downtime. This has led to a general feeling among ATC users of the system that it provides doubtful message exchange integrity and a real potential to add significantly to controller workload.

This situation has led IFATCA to accept the following Policy at its recent Annual Conference held in Toulouse, France:

“FANS-1/A CPDLC has limitations. These shortcomings must preclude further proliferation of this technology, into states of the world where it is not currently deployed. Once the Aeronautical Telecommunications Network (ATN) data link system is deployed, use of the FANS-1/A CPDLC shall be replaced by the ATN system and FANS-1/A systems shall not be accommodated in the ATN, as this would seriously degrade the operational suitability of the ATN.”


The purpose of this paper is to explore the nature and development of FANS 1/A in order that the above policy can be further developed.


It needs to be emphasised that the above policy applies only to the CPDLC element of FANS 1/A. It is not intended to refer to ADS applications that may be supported by the system.

The Aeronautical Telecommunications Network (ATN) in concept is the central plank of CNS/ATM. Unfortunately it is also the most complex and consequently the slowest developing.

The ICAO standards for the ATN have been validated and are expected to be approved late in 1998.

The European regional ATN implementation plan and will be subject to ICAO approval in 1999. A start to the implementation of mobile ATN data services is expected at the end of 2004 with Europe wide services expected to be available one year later.

Several ATN development projects are underway in the Asia Pacific region among them the ASIATN project which is a joint venture between Thomson Airsys and Airservices Australia.

The FANS 1 project was initiated by the Boeing Commercial Airplane Group in response to a need expressed by various airlines to obtain early benefits from the developing CNS/ATM technology. Airbus Industries later embraced that philosophy by fielding the FANS A system.

FANS 1/A set out to implement ADS and datalink using what was available of the ATN definition and existing satellite communications protocols (AIRINC 622). It is purely an aircraft system in contrast to the ATN which will, by its specification guarantee end to end communications standards and integrity. ATC automation elements have been developed to support FANS 1/A they have however, been essentially independent efforts operating from a common but in many ways immature set of standards.

While FANS 1/A was only designed for low density transcontinental and oceanic airspace it has been instrumental in providing valuable experience in the vital areas of interfaces and procedures.

Given that this effort represents a considerable investment by a number of airlines it is reasonable to expect that there will be strong pressure on ATS providers, particularly those in the Asia Pacific region to deliver a service using, or at least accommodating, this technology.

Draft material has been prepared by the ATN and ADS panels of ICAO for addition to the ICAO Comprehensive ATN Manual (CAMAL). This material sets out to provide guidelines to States that implement CNS/ATM systems to support air traffic services using the ATN and that elect to accommodate FANS 1/A aircraft.

This material divides the issue into two parts, the operational accommodation and the technical accommodation.

1. The operational accommodation section highlights the need to consider three scenarios:

a) That of FANS 1/A and ATN aircraft operating in a common ATN airspace:

i. FANS 1/A operating on the same flight in both ATN and FANS 1/A airspace;

ii. Different levels of operational requirements in different kinds of ATN airspace.

2. The technical accommodation section contains several elements which in many ways reflect the concerns expressed in the IFATCA policy on FANS 1/A and on ADS, for instance:

a) “Considerations should be given to avoid having two applications for the same operational purpose interfacing the pilot or controller in different ways. Operationally significant differences can not be tolerated for either pilot or controller.’

b) ‘Communication services provides integrity measures to protect against the failure conditions, such as undetected corruption of data, undetected mis-addressed messages, and undetected messages received out of sequence.’

c) The decision on the FANS 1/A technical accommodation solutions should consider the results of an assessment to determine the cost and technical feasibility to implement integrity measures and development assurance methods necessary to show compliance with operational requirements.

A general note adds the caveat:

“Further evaluations of functionality, performance, safety and interoperability are needed to determine if FANS 1/A data communication and surveillance capability is acceptable for uses other than primary means of controller pilot communication in oceanic and remote airspace.”

Writing for the ICAO Secretariat, Chris Dalton (well known for his work in IFATCA particularly in the Asia Pacific Region) proposes some assumptions as useful for the development of a ground accommodation strategy. These assumptions include:

  • The goal is to migrate to uniform ATN compliance;
  • ATN SARPS will not be changed to accommodate FANS 1/A aircraft;
  • Differences in handling aircraft are to be minimised for both the controller and the flight crew;
  • Mixed fleet equipage ie. FANS 1/A and ATN may exist for a period of time.


ATN can hardly be said to be ‘around the corner’ in the absence of FANS 1/A there is currently no other vehicle by which ADS or Datalink can properly develop.

There is concern though that the third party communications providers concerned are not capable of providing the level of reliability, availability and integrity required for an Air Traffic Control system.

The very airspaces in which FANS 1/A is currently being used are likely to be the areas in which the ATN is first deployed owing to the low density of operations within it. It is therefore reasonable to expect considerable pressure to continue to accommodate FANS 1A for at least an initial period.

While there is no immediate pressure to migrate the use of FANS 1/A CPDLC to denser airspaces, there will be continued pressure to expand its use in Oceanic and low density transcontinental airspace.

It may well benefit IFATCA and its MAs to take a more pragmatic approach to the future of FANS 1/A by participating in the development of the ATN and cooperating with ICAO in the work being done in the highly complex area of transition to a uniform CNS/ATM environment. Areas of particular interest should be:

  • Non proliferation of the FANS 1/A CPDLC application in its current form to other than oceanic and low density transcontinental airspace.
  • The protection and assurance of data integrity.
  • The proper integration of transitional systems in terms of ATC automation systems and controller interfaces.


FANS1 – Air Traffic Services Systems Requirements and Objectives 747 – 400 – presented by BCAG as RGCSP WG/A IP/4 October 1995.

Draft text on FANS 1/A accommodation for inclusion into the CAMAL Part II, Chapter II – Attachment 1 to 98ATS095.

In Search of a Strategy – ICAO Journal March 1998.

Last Update: September 28, 2020  

March 10, 2020   777   Jean-Francois Lepage    1999    

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