On-Board zone navigation equipment (RNAV), as with all navigation instruments, has accuracy requirements. These requirements are enshrined in the concept of PBN, and are expressed in the form of so-called navigation specifications RNAV and RNP and can be installed for air routes, airfield schemes or for entire regions.
In the late 80's, ICAO issued guidance on RNP (Required Navigation Performance) (not to be confused with the RNP specification of the PBN concept). The main focus of the RNP manual was on the accuracy of airborne and ground equipment. RNP-1 and 4 were required to monitor current navigation characteristics as well as issue warnings. Accuracy requirements were expressed in nautical miles of linear lateral deviation, for example RNP-1 means that with a probability 0.95 linear lateral deviation must remain within &pl;1 nautical mile relative to the axis of the track (probability 0.95 corresponds to two RMS errors). It is also said that during 95% of the time the flight must pass within one nautical mile of the axis of the track. This does not mean that the remaining 5% can be flown off-piste. The route means any line of a way, including operatively set, and not only the published route of ATS.
Since the ICAO document had the status of recommended practice, many States set their own requirements. In fact, these requirements were in line with the RNP, but there were no requirements for monitoring current navigation characteristics by on-Board equipment. There was only a requirement for accuracy of navigation, expressed in nautical miles. It was connected first of all with features of the navigation equipment operated at that time.
In the US, the standards RNAV-5 and RNAV-1 were in force, and in Europe in General, similar B-RNAV and P-RNAV. Requirements B-RNAV or Basic-RNAV corresponded to lateral accuracy of 5 nautical miles, and P-RNAV or Precision-RNAV – 1 nautical mile. BRNAV requirements were introduced in the European region in 1998. The PRNAV rules were intended to be applied in the aerodrome area.
The next step was the concept (PBN – performance based navigation) or performance based navigation, which combined and systematized all pre-existing requirements for navigation accuracy.
The PBN concept assumes a more flexible approach, with the following hardware requirements: accuracy, integrity, availability, continuity, and functionality. From the point of view of practical application of PBN, only accuracy and functionality of system are important, other parameters are interesting to developers of the equipment and those who allows system to operation according to this or that specification. In principle, it is not very important what means will be used to fulfill the conditions set out in a particular navigation specification. Each specification requires a choice of navigation sensors, i.e. the specified accuracy can be achieved using, for example, DME/DME and GNSS. The refusal to bind the requirements to a particular equipment allowed to optimize the structure of the airspace.
There are two types of specifications: RNP and RNAV, the main difference of which is the requirement to monitor and alert the crew in case of failure to maintain the specified characteristics for the RNP specifications.
The concept of PBN in the future involves a transition to RNP specifications, which will allow for a higher density of the route network in the face of growing traffic volume.
The two main aspects of the PBN application are the requirements set out in the relevant navigation specification, as well as the infrastructure of the navigation AIDS (both terrestrial and satellite) that support the operation of the system.
The navigation specification is a set of requirements for the equipment of the aircraft and for the flight crew, which are necessary to ensure the process of zone navigation within the established airspace.
For both the RNP and RNAV designations, the following number (where given) indicates the accuracy of horizontal navigation in nautical miles, with a probability of 0.95 the aircraft must be within specified limits.
Each specific aircraft is certified for compliance with certain navigation specifications, depending on its equipment and characteristics of the navigation system. Flight crew members must also undergo appropriate training.
Due to the fact that the navigation specification is a set of requirements where accuracy is not the only criterion, an aircraft that has a tolerance of, for example, RNP-1 may not meet the less stringent requirements of RNAV-5.
Today, the pre-existing PRNAV, BRNAV, US-RNAV requirements have been replaced by PBNspecifications. According to the concept, each specification has its own purpose.
Information about the PBN specification in coded form is indicated in field 18 of the flight plan, thus, ATS personnel are notified about the admission of the aircraft performing a particular flight to navigation in accordance with a certain specification.
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