Direct Controller Pilot Communications (DCPC)

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Direct Controller Pilot Communications (DCPC)

36TH ANNUAL CONFERENCE, Taipei, Taiwan, 17-21 March 1997

WP No. 114

Direct Controller Pilot Communications

This paper will:

a)  discuss the concept of Direct Controller Pilot Communications (DCPC);

b)  highlight how this concept affects proposals to reduce required separation minima, especially within Oceanic/ Remote airspace;

c)  outline the often heated discussions that have gone on within ICAO between the RGCSP (Review of the General Concept of Separation Panel) and the ADSP (Automatic Dependent Surveillance Panel);

d)  relate that there is not general agreement even as to what constitutes direct voice communications;

e)  discuss the concept of Required Communication Performance (RCP) and how it may affect DCPC, and

f)  propose IFATCA policy regarding DCPC.

As work matures on ICAO standards for data link communications systems to provide Air Traffic Services (ATS) and as initial data link systems such as FANS are implemented by various States, there is considerable discussion regarding whether and how this new technology can be used to reduce separation standards, especially in Oceanic/Remote FIR’s. The pressure for these reductions comes principally from the airline industry looking for financial benefits and is being felt especially in those States with early data link systems and in ICAO.

Two ICAO Panels, the RGCSP and the ADSP, are currently working on standards that affect the concept of DCPC. There has been heated debate between these two Panels regarding this work, with the ICAO RAC/SAR acting as moderator through the respective Panel Secretaries.

The RGCSP initially introduced the term DCPC. In the report on the Ninth Meeting of the RGCSP, specifically Appendix B to the Report on Agenda Item 2, par. states, “Direct controller/pilot communication shall be maintained while applying a distance based separation minima. Direct controller/pilot communication shall be voice or controller/pilot data link communications (CPDLC).” Further in the same section, par. states, “For aircraft cruising, climbing or descending on the same track, the following separation standards may be used:” and for both 80 NM and 50 NM separation standards the communications requirement states, “Direct controller/pilot communication.”

The work of the ADSP seems to present a more stringent operational requirement. In the Draft ICAO Manual of Air Traffic Services (ATS) Data Link Applications, which the ADSP has submitted to the ICAO Air Navigation Commission (ANC) with a proposal for publication, Part I Chapter 3, par. 3.4.2 states the following Generic Operational Requirement, “In any data link based ATS, provision must always be made for direct pilot-controller voice communications.” It is extremely important to keep in mind that this draft Manual, if accepted for publication by the ANC, will have the status of Guidance Material and as such does NOT have the regulatory nature of ICAO Annexes or of Doc. 4444 – PANS/RAC.

Because the draft Manual would only have the weight of Guidance Material, the ADSP proposed two other items to the ANC. In the ICAO report on the Fourth Meeting of the ADSP, Appendix A to the Report on Agenda Item 4, the Panel proposed the following amendment to Annex 11, Chapter 6. Under 6.1.1 General, par. is proposed to read, “Suitable arrangements shall be made to enable direct controller-pilot voice communications whenever the loss of CPDLC could adversely affect the level of safety.”

If the above proposed Annex change is accepted by the ANC, the applicability date would likely be late 1998. Because of this and because of the rapid pace of developments in the area of data link, the ADSP included in the same report the following recommendation to the ANC.

“Recommendation 4/4 – Use of controller pilot data link communications (CPDLC) without direct controller-pilot voice communications. That, until such time that ATM requirements for communications, including the concept of required communications performance, have been fully developed by ICAO, the use of CPDLC without complementary direct controller-pilot voice communications should not be considered as an essential element to provide the necessary level of safety.”

The crux of this important debate seems to be that the RGCSP states that separation standards, specifically longitudinal standards, may be reduced and the communications requirement for this reduction is for DCPC. Further, the RGCSP states that DCPC can be either voice or data link (CPDLC), and it is unclear whether the voice in this requirement must be direct voice communication or whether third-party HF voice through a communicator would suffice. The ADSP draft Manual states that when any ATS is provided over data link, direct controller-pilot voice communications capability must be provided. The Annex 11 proposed change would require that in situations where the loss of CPDLC could reduce the level of safety (and this could arguably be the case where separation minima are reduced based on data link) direct voice communications capabilities are mandatory.

It must also be pointed out that in the organizations that are currently discussing direct voice communications, there is not even a general consensus as to what constitutes direct voice communications. In the VHF environment, when the controller keys the mike and the communication is delivered to the cockpit nearly simultaneously, direct voice communications is not a difficult concept to understand. However, the picture is not so clear in the HF and Satcom environments.

In States that utilize HF radios for ATC, there are a couple of setups that have been instituted or proposed to meet direct voice communications requirements. One is a system that uses third- party communicators between pilots and controllers but which gives the controller a capability to directly transmit over all HF channels. This system is essentially a one-way, direct voice communication capability. Another system would also use third-party communicators, but either the pilot or controller could request that the HF operator set up a “patch” that would allow direct voice communications between the pilot and controller.

In the Satcom environment, at least one State has published satcom phone numbers of ATS Units for use by pilots. This allows pilots who need to make emergency or non-routine communications to place a call to the supervisor’s desk in the area in which the appropriate control sector is located. The phone can then be delivered to the appropriate controller, resulting in direct controller-pilot voice communications. Also, satcom phone numbers can be listed in flight plans that allow controllers to dial direct satcom phone calls to specific aircraft.

In addition, satellite communications service providers are attempting to develop capabilities that would allow direct satcom calls to be made to specific controller positions. At this time, any such capability would require elaborate and time-consuming set up procedures.

There is effort underway at the ICAO level and in several States to progress the concept of Required Communications Performance (RCP). This concept is seen as a complement to Required Navigation Performance (RNP). It is hoped that if RCP standards can be achieved, it may answer the questions of what levels of voice communications are required to complement data link capabilities. This work is progressing in the United States by the FAA and RTCA, and at the ICAO level the ANC has tasked the ADS Panel to be the coordinating body, working with the RGCSP and the Aeronautical Mobile Communications Panel (AMCP), to develop standards for RCP. It should be noted that ICAO envisions RCP, RNP, and Required Surveillance Performance (RSP) as joint elements comprising Required Total System Performance (RTSP).


As data link becomes an important means of delivering ATS, there are crucial questions that must be answered before this technology is used for safety-critical communications. This need is especially true where a data link communications system is the primary, or even integral, element in allowing the reduction of separation standard minima.

IFATCA, along with IFALPA, are crucial players in answering these questions because these two organizations represent the human beings that are the two vital ends of any ATS communications system. Because of this, IFATCA, through this Committee, must formulate a clear, formal position on these issues.

It is recommended that:

“In any ATS system, where data link is considered a safety-critical element of that system, data link based ATS must be accompanied by direct two-way controller-pilot voice communications which is also safety critical. This direct voice functionality shall be rapid, continuous and static free.”

“If, however, the provision of data link ATS is not used as a factor in either reducing separation standards or increasing airspace capacity, the voice capability need not be of a direct nature.”

“The definition of direct as used in voice or data link communications requires that no third human party is involved in the set up and/or delivery of these communications. Any set up procedures by either the pilot or the controller must be minimal and nearly instantaneous.”

Current policy on datalink to be amended as pertains to the table in that policy. With respect to the tables detailing both the rows for Oceanic Continental Low Density and for Oceanic High Density, under the column for Tactical Separation, should read,

“Voice, either alone or in addition to Data Link.”

Last Update: September 28, 2020  

March 4, 2020   951   Jean-Francois Lepage    1997    

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