Investigation of the Nomenclature used in the Acronyms CIB & CIC

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Investigation of the Nomenclature used in the Acronyms CIB & CIC

42ND ANNUAL CONFERENCE, Buenos Aires, Argentina, 17-21 March 2003

WP No. 84

Investigation of the Nomenclature used in the Acronyms CIB & CIC

Presented by SC1


1.1  WP 82/2001 presented by SC1 at Geneva reviewed the concept of Controller Intervention Buffer (CIB) and Controller Intervention Capability (CIC) as it relates to the development and application of ATC separation standards and procedures.

1.2  WP 87/2002 expanded on that work in an attempt to address some concerns over the possible use of these concepts as a controller performance measurement regime.

1.3  IFATCA policy on the CIB/CIC concept now states:

  • The Controller Intervention Buffer be defined as:
    • The time required for the Air Traffic Controller to intervene ensuring that a collision would be averted in the event that a separation standard being applied breaks down. This will include an allowance:
      • to recognize the ‘blunder’,
      • to formulate a solution,
      • to convey instructions to the pilot,
      • for the pilot to react and cause the aircraft to achieve the required change of trajectory.
  • A Controller Intervention Buffer should be included in the development and specification of any separation minima where controller intervention is used as a risk mitigator.
  • All of the parameters used to determine the Controller Intervention Buffer should be part of the documentation of any such separation minima.
  • ATC systems should be developed with the capability to monitor relevant Controller Intervention Capability (CIC) parameters and warn controllers when they fall outside the values used in determining separation standards in use so that alternative standards can be applied.


1.4 Concerns remain in some MAs that the nomenclature chosen is not appropriate for the concept and has the potential to cause confusion.


2.1  It is universally understood that Safe and orderly air traffic management relies on communications, navigation and surveillance (CNS).

2.2  The Required Navigation Performance (RNP) concept has been developed to define the various levels of navigational accuracy that can be relied upon in designing airspace and separation standards. The RNP value defines the positional accuracy that is achieved 95% of the time by an aircraft. For example and aircraft operating to RNP 4 can be expected to be within 4nm of its planned or cleared track at least 95% of the time. Airspace buffers can then be added to increase the containment level.

2.3  It is the ATC system that is most often used to control the percentage of navigational errors (and thus the collision risk for the subject airspace) that lie outside the containment limits based on the RNP value in use.

2.4  CIB and CIC have been put on the work programme of SC1 as a result of RGCSP discussions in the development of the “Manual on Airspace Planning Methodology for the determination of separation minima” (ICAO doc 9689, first edition 1998). Appendix 5 of that document, Assessment of longitudinal separation in the Asia/Pacific regions, introduces the terminology “Communication and Controller Intervention Buffer”. The reason for this was “that rather than base the calculations solely on the time interval to the next distance check; the model uses the concept of a communication and controller intervention buffer”. IFATCA was asked its support for the introduction of the communication controller intervention capability/buffer concept in the anticipation of the RCP concept.

2.5  Doc 4444, PANS-ATM, para “Longitudinal separation minima based on distance using RNAV where RNP is specified” refers the communication criteria to the safety assessment as referenced in para 2.4.

2.6  The latest PANS-ATM amendment, 28 Nov 2002, “Longitudinal separation minima based on ADS” refers to a safety assessment used to determine these separation minima, including examples of communication media and operational assumptions that can satisfy the intervention requirements. This safety assessment is a revised version of the assessment as referenced in para 2.4 and uses the same terminology.

2.7  The CIB and CIC concept has been investigated by SC1 in recognition of the fact that the ability of the ATC system to recognise and initiate correction of navigational ‘blunders’ by aircraft is a critical factor in the risk profile of most separation standards used by ATC. Over the years it seems to be forgotten that the origin of CIB and CIC was developed for communication purposes only.

2.8  To date there are no general principals or parameters by which the performance of the surveillance and the communications elements of the ATM trinity (CNS) can be measured.

2.9  Current IFATCA policy on CIB/CIC is designed to give guidance to IFATCA representatives on the various IFATCA and industry bodies in their efforts to correct this basic deficiency.

2.10  Quite reasonably there is nervousness in some ATC circles when ATC system performance parameters are advocated. This is particularly so when the nomenclature used suggests that it is the Controller’s performance alone that is being measured. The terms Controller Intervention Buffer and Controller Intervention Capability may give such an impression.

2.11  SC1 investigated a reason to change “controller” in the terminology CIB/CIC to “ATC System Intervention Buffer”/”ATC System Intervention Capability”. Discussions took into account para 2.4, 2.5 and 2.6 and concluded that a change would no longer serve the purpose as referenced in those paragraphs.


3.1 It has been concluded that changing the nomenclature used in the acronyms CIB & CIC would take the concept much further than its original intent. This is based on the information sourced from the SASP documentation. It was therefore decided that the policy remains as is.


It is recommended that:

4.1 This paper be accepted as information material.

Last Update: September 29, 2020  

March 21, 2020   152   Jean-Francois Lepage    2003    

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