Figure: Communications capabilities and performance related to separation assurance, from ICAO Document 9869, Figure 3-2.
Most pilots who have flown internationally in the last decade or so are well acquainted with the concept of Required Navigation Performance (RNP), the idea that where you can fly will be determined on how accurately you can fly and how well the system alerts you when things are less than promised. While it isn't a perfect statement, you can think that the XX in your RNP-XX relates to that accuracy. The same concept holds true for communications and surveillance. In the case of communications, the number attached to your Required Communications Performance (RCP) is the number of seconds it takes for an instruction to travel from the ground to you and your acknowledgement back to the ground. Does it matter? Yes, the lower the number the tighter the airspace you will be allowed to fly. Put another way, the higher the number, the more airspace around the world that will be denied you.
What follows are quotes from various sources, listed below, as well as my comments in blue.
[ICAO Doc 9869, ¶1.1.4] The fourth meeting of the Aeronautical Mobile Communications Panel (AMCP/4) (Montreal, April 1996) recognized the absence of objective criteria to evaluate communication performance requirements. This objective criteria was seen as a set of values for parameters, which would be based on the operational requirements for communication systems in the various phases of flight. The meeting agreed that there was an urgent need to assess the various technical options of communication systems against such a set values for these parameters. The term RCP type is used to denote a set of values for these parameters.
This all grew out of the initial efforts to formalize the Future Air Navigation System (FANS) that led to the development of a Required Navigation Performance (RNP) standard. It may not seem as significant as the revolutionary changes seen in navigation, but RCP is the underlying principle behind getting rid of HF and moving toward SATCOM. That also spawned the need to differentiate SATVOICE versus SATCOM.
[ICAO Doc 9869, ¶2.2]
- The RCP concept characterizes the performance required for communication capabilities that support ATM functions without reference to any specific technology and is open to new technology. This approach is essential to evolving operational concepts using emerging technologies. An ATM function is an individual operational component of air traffic services. Examples of ATM functions include the application of separation between aircraft, the re-routing of aircraft, and the provision of flight information.
- The RCP concept assesses operational communication transactions in the context of an ATM function, taking into account human interactions, procedures, and environmental characteristics.
- The contribution of the human can be significant to RCP. Communication is the accurate transfer of information between sender and receiver, the content of which can be readily understood by both.
- An operational communication transaction is the process a human uses to send an instruction, clearance, flight information, and/or request, and is completed when that human is confident that the transaction is complete.
- The RCP concept is based upon “operationally significant” benchmarks to attain confidence that the operational communications supporting the ATM functions will be conducted in an acceptably safe manner.
The benchmark of choice is the round trip time between a controller's instruction to a pilot and the pilot's acknowledgement back to the controller.
- The basis for the development of the RCP concept was the need for objective operational criteria, in the form of an RCP type, to evaluate a variety of communication technologies. Once these criteria have been set and accepted, a specific implementation, considering system technical and human performance, may be assessed for its viability against acceptable operational criteria.
- An RCP type is a label (e.g., RCP 240) that defines a performance standard for operational communication transactions. Each RCP type denotes values for communication transaction time, continuity, availability, and integrity applicable to the most stringent operational communication transaction supporting an ATM function.
[ICAO Doc 9869, ¶3.2]
- In order to simplify RCP type naming convention and to make the required communication transaction time readily apparent to airspace planners, aircraft manufacturers and operators, the RCP type is specified by the value for the communication transaction time associated with the ATM function.
- An RCP type comprises values assigned to the parameters: communication transaction time, continuity, availability, and integrity.
- RCP type parameters
- Communication transaction time - The maximum time for the completion of the operational communication transaction after which the initiator should revert to an alternative procedure.
- Continuity - The probability that an operational communication transaction can be completed within the communication transaction time.
- Availability - The probability that an operational communication transaction can be initiated when needed.
- Integrity - The probability that communication transactions are completed within the communication transaction time with undetected error.
This is good stuff for a comm geek but really not that pertinent to a pilot. But it helps to understand what is to follow:
Figure: Recommended RCP Types, from ICAO Document 9869, Table 3-1.
[ICAO Doc 9869, ¶3.3]
- There may be multiple operational communication transactions that support an ATM function. These transactions are assessed to determine the most stringent. The value for the communication transaction time parameter is based on the time needed to complete the most stringent transaction.
- The assessment would take into consideration the time needed to safely execute the contingency procedure and can include simulations, demonstrations, operational trials, and analysis of empirical data applicable to the operational communication transaction times needed to support the ATM function.
- Separation assurance is an ATM function for which the operational communication transaction time can be determined by collision risk modeling. Collision risk modeling considers the operational communication transaction times in the communications and controller intervention buffer supporting separation assurance. [The figure at the top of this page] illustrates the operational communication transaction in the context of communications and controller intervention buffer.
There you see the crux of the RCP issue for a pilot. If you are flying in an environment where you have 50 nm or more lateral spacing, you are probably flying in an RCP-400 environment. The turn around time from the controller to the radio operator to you and back is 400 seconds. An HF will suffice. But, on the other hand, if you are flying with only 30 nm of lateral spacing and reduced longitudinal separation, you are probably dealing with an RCP-240 environment. Now you need CPDLC. If you combine CPDLC with ADS, you can get even lower with a thing called Required Surveillance Performance (RSP):
Figure: Examples of applying RCP and RSP specifications, from ICAO GOLD, Tables 2-3 and 2-4.
Portions of this page can be found in the book International Flight Operations, Part IV, Chapter 1.
ICAO Document 9869 AN/462 (Draft), Manual on Required Communication Performance (RCP)
ICAO Global Operational Data Link Document (GOLD), International Civil Aviation Organization, Second Edition, 26 April 2013