PBN Code Selection

PBN is the acronym for Performance Based Navigation. From the FAA website:

Performance Based Navigation (PBN) comprises of Area Navigation (RNAV) and Required Navigation Performance (RNP) and describes an aircraft's capability to navigate using performance standards. RNAV enables aircraft to fly on any desired flight path within the coverage of ground or space based navigation aids, within the limits of the capability of the self-contained systems, or a combination of both capabilities. 

RNP is RNAV with the addition of onboard performance monitoring and alerting capability. A defining characteristic of RNP operations is the ability of the aircraft navigation system to monitor the navigation performance it achieves and inform the crew if the requirement is not met during an operation. The performance requirements of PBN are conveyed to the operators through navigation specifications. PBN navigation specifications include Advanced RNP (A-RNP), RNP 0.3, RNP 1, RNP 2, RNP 4, RNAV 1, RNAV 2, RNP 10(RNAV 10), as well as RNAV (GPS) and RNAV (RNP) approaches.

Not all pilots need to use PBN codes. In fact, if you only file today using the FAA/Domestic Flight plan format where there is no such capability, you may never need to use a PBN code. Specifying PBN codes adds capabilities beyond what it was possible to specify using an FAA/Domestic flight plan. So if you can fly a particular approach today when filing an FAA/Domestic flight plan, you will still be able to request and fly the procedure without the need to specify a PBN code.

 

RNAV and RNP specifications

RNAV and RNP specifications will include a number which  defines the width within which the aircraft path must remain on at least a 95% basis. So an RNAV 2 specification means that the aircraft path must remain within 2 NM of the centerline of the route 95% of the time, and any deviations outside of the 2 NM must be corrected by the pilot immediately. Pilots are also expected to fly the centerline of the route. Obstacle protection at the minimum route altitude is provided along the route centerline +/- twice the RNAV or RNP specification, so for an RNAV 2 specification, obstacles will be evaluated out to +/- 4 NM at the route minimum altitude.

The difference between an RNAV and RNP specifications is that RNP adds alerting capability. The alerting is to indicate to the pilot that the navigation system is incapable of assuring the accuracy of the navigation system and therefore the pilot must revert to using other means of navigation. 


RNAV Navigation Sensor Types

There is more than one way to determine aircraft position by using different navigation aids for navigating on an RNAV path. Some use ground based systems while others are space based or long range systems. 

 

GPS

The system most pilots are familiar with is GPS. GPS is a space based system and can also be used both for navigation over land and for long range navigation over the oceans. This system is found in all classes of aircraft and may be used in any of the PBN Navigation specifications, although individual systems need to be approved for use in the specific navigation specification. 

 

DME/DME

Over land, a DME/DME RNAV sensor can also be used. This system is based on DME, but is not the type of simple DME found in piston aircraft. Rather it is a sophisticated system involving more than one DME that is driven by a database which knows the frequency, latitude-longitude, and identity of all the DME ground facilities in the coverage area of the database. The system simultaneously tunes and receives multiple DME ground stations to triangulate the current position of the aircraft. This equipment is found in Turboprop and Turbojet class of aircraft and is integrated with an FMS (Flight Management System). This system is mostly limited to being used in RNAV 5, RNAV 2 and some RNAV 1 navigation specifications.

IRU or INS 

Inertial Navigation is also a sensor type that is based on precise measurement of accelerations to determine speed and direction. These systems are initialized to the aircraft position prior to flight, so the beginning accuracy is high, but the accuracy drifts over time and there are limits on how long they can be used in flight without having the position being corrected by other sensors. These systems are used for long range oceanic navigation and when supplemented with other sensors, can be used over land where greater positional accuracy is required. This sensor is limited to being used in RNAV 10 (RNP 10) navigation specifications in Oceanic operation and RNAV 5 and RNAV 2 over land. 

 

DME/DME/IRU

This sensor is based on an Inertial Navigation sensor in combination with a DME/DME sensor. With the DME/DME sensor input, the IRU is continuously corrected for drift when suitable DME reception is available. This expands the capability of the system to be used for RNAV 1 routes over land in addition to RNAV 5, RNAV 2 and RNAV 10 (RNP 10) over oceanic/remote areas.

 

VOR/DME 

This sensor is based on simultaneous reception of a collocated VOR and DME ground facility and is mostly found in General Aviation piston class aircraft. Examples of avionics systems that have this capability include the Bendix King KNS80 and KNS81. Some refer to these type of systems as Rho-Theta RNAV, but these 1980 vintage systems have been largely replaced by GPS. The system allows for simple point to point navigation as long as the aircraft remains in the service volume of the VORTAC or VOR-DME ground stations. The pilot inputs a VOR frequency, a radial, and a distance to define the location of an RNAV waypoint. The computer in the avionics receives the current radial and distance from the VORTAC or VOR-DME being received and using trigonometry calculates a CDI/HSI course deviation and distance to the pilot entered waypoint. This system is limited to being used as a navigation sensor for point to point navigation using RNAV 5 and over land or within VOR and DME ground station reception service volumes.

 

LORAN C 

This sensor has been cancelled by the US Coast Guard and is no longer available in North America and Europe. 

 

PBN Coding

There are currently 24 PBN codes that are used to specify if an aircraft and crew are authorized to fly a particular route or procedure requiring various PBN RNAV or RNP based navigation specifications. PBN codes either imply or specify a navigation sensor that is used to meet the specification. With ICAO, a maximum of 8 PBN codes may be specified in any single flight plan. In many cases, aircraft and crews are approved for more than one means of meeting the RNAV/RNP navigation specification. It is my experience that an aircraft may meet more PBN categories than they actually use, so I am an advocate of just specifying what is needed and not everything that the aircraft and crew are approved for, but rather what they have a use for.

PBN codes are specified using a letter and a number. They  are included in field 18 after the keyword PBN/. The letter specifies the relevant RNAV or RNP performance navigation specification and the number describes either the sensor used to provide the capability or a sub capability. For example, all the D PBN codes apply to the RNAV 1 Navigation specification and the number indicates the sensor type. D2 indicates the sensor is GPS. D3 indicates the sensor is DME/DME, and D4 indicates the sensor is DME/DME with Inertial Navigation.  D1 indicates that  the aircraft is equipped with all the sensors. When a PBN code uses a sensor or implies a sensor, the basic ICAO equipment code must also specify the sensor. So D2 is RNAV 1 using GPS, that means that the ICAO equipment code of G must also be specified. D3 required DME/DME, so the ICAO equipment code must have a D for DME specified. If D4 is specified, then the ICAO equipment must also specify both D for DME and I for Inertial Navigation. Using D1 would require specifying D, G, and I in the ICAO equipment as all sensors are being claimed. A failure to be consistent between the sensors and the PBN codes will result in a rejection of the flight plan. Also, if any PBN codes are specified, R must also be specified in ICAO equipment. Don’t specify the R if you don’t specify a PBN code.

 

RNAV 10/RNP 10 (A1) 

This PBN specification is used for flight in Oceanic airspace. To fly in much of the Oceanic airspace between FL285 and FL420, aircraft must be capable of navigating RNP 10. Just because an aircraft is equipped with systems that support this capability is not sufficient to include the A1 specification. For a part 91 operation, an FAA Letter of Authorization from the local FAA Office is required to be obtained and carried on board the aircraft. Not many piston aircraft will be specifying this code.

 

RNAV 5 (B1 thru B6)

The RNAV 5 PBN navigation specification supports basic point to point navigation. A route that is defined as direct from one airport to another airport is a point to point route. Any route that does not depend on the use of airways, but is rather a great circle (direct) route between points would use RNAV 5. The route can be established by the pilot merely defining the departure and destination airports with any number of points in between. Pilots are expected to fly  the centerline of the defined route with the pilot remaining within +/- 5 NM of the centerline at least 95% of the time.

In the US, RNAV 5 is assumed if you have coded a G for GPS, so there isn’t much use for using the B2 PBN code. But, If you are not GPS equipped, RNAV 5 has utility when you have another form of point to point navigation such as DME/DME (B3), VOR-DME RNAV (B4) equipment, or Inertial equipment (B5) will allow you to file a point to point route. RNAV 5 is required in Europe and is called BRNAV (Basic RNAV). Any GPS that is approved for IFR enroute and terminal operation qualifies for specifying this PBN code. I don’t bother to specify B2 (RNAV 5 - GPS) because it is not needed if you specify G in your ICAO equipment.

B6 specifies RNAV 5 using a LORAN sensor. Since LORAN is no longer supported in the US, this code is no longer used. B1 indicates the aircraft is equipped with all the possible senor types except LORAN. If B1 is specified, the aircraft must have ICAO equipment codes of D, G, I, and either S or O.

 

RNAV 2 (C1 thru C4)

The RNAV 2 PBN navigation specification is used for flying airways based on RNAV waypoints. In the US, T routes (low altitude RNAV routes) and Q routes (high altitude RNAV routes) are examples of airways that are based on RNAV. These routes are the same width as airways with the low routes having a defined MEA.  Pilots are expected to fly  the centerline of the RNAV route and remaining within +/- 2 NM of the centerline at least 95% of the time.

All GPS systems approved for IFR for enroute and terminal operations qualify for the RNAV 2 PBN specification. Pilots should specify C2 if they have a GPS. Without a GPS, one would need to specify either D3 (RNAV 2 using a DME/DME sensor) or D4 (RNAV 2 using a DME/DME/INS sensor). 

C1 indicates the aircraft is equipped with all three types of sensors and the ICAO equipment codes of D, G, and I must also be specified to avoid an error. This code is highly unlikely to be used by piston aircraft.

 

RNAV 1 (D1 thru D4)

The RNAV 1 PBN navigation specification is used for flying RNAV SID and RNAV STAR procedures. These are SID and STAR procedures with RNAV in the title. This is one of the few PBN codes that add capability when switching from using  the FAA/Domestic Flight plan form to using the ICAO form. The RNAV 1 PBN codes D1 thru D4 are essential if you plan to file or fly RNAV SID or RNAV STAR procedures, as RNAV 1 PBN capability is required to fly them. Without one of the D codes being specified, the ATC computer will reject any flight plan that includes an RNAV SID/ STAR procedure. This is a common reason that FAA/Domestic flight plans get rejected because you simply can’t file a flight plan with an RNAV SID or STAR  as there is no means of indicating the aircraft meets RNAV 1 capability.

Not all GPS systems are approved to fly RNAV 1 procedures including most of the legacy TSO C129 pre-WAAS systems which are not approved. The only pre-WAAS GPS systems that I am aware of that are approved to fly these procedures are the GNS430/530 and G1000 systems from Garmin. All of the WAAS version GPS systems are approved, so if your GPS is WAAS, it can fly these procedures.  If you have a GPS system and don’t know if it qualifies to fly one of the RNAV 1 SID/STAR procedures, you can look it up in this FAA document  FAA AC-100A Compliance Matrix  A dead giveaway to check If the GPS system is approved or not to fly the RNAV SID/STAR, the procedure will not be in the database if the GPS is not approved. Examples of common GPS systems that are not approved to fly these kinds of procedures include the KLN90B, KLN94, GNC300XL.

If your GPS is approved to fly the RNAV 1 SID/STAR procedures, specify D2. Other sensors may be used to fly these procedures unless the chart has a NOTE limitation on it such as “GPS required” or “DME/DME/IRU or GPS required.”

D3 is specified if the sensor is DME/DME. This sensor depends on satisfactory multiple DME stations in the vicinity of the procedure and it is often the case that these type of sensors are not permitted to use a particular procedure. D4 is specified if the aircraft is equipped with DME/DME/IRU sensor.  

D1 is specified if the aircraft is equipped with all three sensor types and the aircraft must have ICAO equipment codes of D, G, and I specified. It is highly unlikely that a piston aircraft will be able to legitimately specify this code.

 

RNP 4 (L1)

This PBN Navigation specification is used for flight in Oceanic airspace. To fly in more and more of the Oceanic airspace between FL285 and FL420, aircraft must be capable of RNP 4. Just because an aircraft is equipped with systems that support this capability is not sufficient to include the L1 specification. For a part 91 operation, an FAA Letter of Authorization from the local FAA Office is required to be obtained and carried on board the aircraft.

This navigation specification is only based on GPS as the sensor type, so G must also be specified.

 

RNP 1 (O1 thru O4)

These PBN navigation specifications may be used on some SIDs and STARs. The default SID will use RNAV 1, RNP 1 will be used when a SID contains an RF (Radius to Fix) leg or when surveillance (Radar) monitoring is not desired for when DME/DME/IRU will be used. An RF leg is an advanced RNAV capability and defines a curved route to join two waypoints. The center point of the radius is set to the inside of the curve so that the path is tangent to the two points. This allows for a smooth curve between the two points and takes less airspace to construct and results in a more repeatable route by aircraft than a straight segment between the two waypoints. A straight segment between two points needs to account for variations in when the aircraft will begin and end the course change at the waypoints. Only certain GPS systems are capable of  support this type of leg and even then there are other equipment requirements such as a Flight Director, an HSI with Auto Slew, an or an autopilot with roll steering. These procedures are rare and typically are noted for turbojet only and GPS only. The Atlanta airport, ZELAN 4 RNAV (RNP) SID is an example.

 

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Image 1. Zelan4 RNAV (RNP) SID

O2 is the code used when the navigation sensor is GPS. O3 is used when the navigation sensor is DME/DME. O4 is used when the navigation sensor is DME/DME/IRU. 

O1 is specified if the aircraft is equipped with all three sensor types and the aircraft must have ICAO equipment codes of D, G, and I specified. 

It is highly unlikely that a piston aircraft will need to legitimately specify this navigation specification.



RNP APCH (S1 or S2)

These two PBN specifications are used to indicate the aircraft is capable of flying RNAV (GPS) approaches to the LNAV or LNAV/VNAV lines of minima. Naming of these approaches has evolved from being called GPS approaches to being called RNAV (GPS) in the US and outside of the US RNAV (GNSS). ICAO is recommending that the names be changed once again to be RNP (GPS) approaches, although the US will retain its current procedure names. I can’t find any ATC system that makes actual use of these codes and they don’t appear to have an impact on filing. If a pilot requests to fly an RNAV (GPS) approach, they will be cleared to fly it, although you should at least specify you have a GPS. S1 indicates that the aircraft is capable of flying an RNAV (GPS) approach to LNAV MDA minimums. S2 indicates the ability to fly either the LNAV MDA or to fly vertical guidance to a LNAV/VNAV DA. AC 90-105A allows these procedures to be flown in US airspace using either WAAS or Baro VNAV for the vertical guidance. 

Do not specify both S1 and S2, only one may be chosen. A TSO C129 GPS certified to fly approaches  without Baro VNAV capability can specify S1. A WAAS GPS may specify S2 (US only) as can aircraft with Baro VNAV based vertical guidance for approach operations. I don’t specify either because as I noted earlier, it does not affect filing a flight plan or obtaining a clearance to fly the approach. 

 

RNP AR APCH (T1 or T2) 

These codes are used to indicate that the aircraft and crew are approved to fly approach procedures with the title RNAV (RNP). The AR in the specification stands for Authorization Required and this statement appears as the first note in the approach notes on every chart. These procedures do not appear in the databases of GPS equipment that are not approved to fly them. The pilot requires special training and FAA approval along with specialized equipment only found on Turbojet/Turboprop aircraft. T1 is used for RNP AR approaches with RF (Radius to Fix) capability. Radius to fix is an advanced RNAV feature that guides an aircraft on a constant radius path between two waypoints. It requires the use of a Flight director and /or an autopilot.  T2 is used for aircraft and crews that are qualified to fly RNP AR Approaches, but that do not support RF capability. Only T1 or T2 should be specified. If you were flying an aircraft using the FAA/Domestic Flight plan, your aircraft would not qualify for either of these codes and it is highly unlikely that any piston aircraft will legitimately specify these codes. 

 

Using NAV/RNV

PBN codes were introduced in 2012, but RNAV SID and STAR procedures were introduced in 2008. In the interim period, the FAA devised another means of indicating the aircraft met the RNAV 1 or RNAV 2 Navigation specification requirements. This was accomplished by specifying Z in the ICAO equipment and using the NAV/ sub field in field 18. The coding works like this:

 

Specify NAV/RNVD1E2A1 if the aircraft is capable of meeting the RNAV 1 specification on departure (D1), RNAV 2 specification enroute (E2), and RNAV 1 specification on arrival (A1). The D1, E2, and A1 can be in any order or a specification may be omitted, for example D1A1 would be used if the aircraft only met the RNAV 1 specifications for departure and arrival. One could also selectively specify that RNAV 1 was not to be used for departure (no RNAV SID desired) by specifying D0 or not including the D1. The same applied to A1 or A0 or E2 or E0. For the most part, these codes have been obsoleted by PBN codes, but because they offer a means of selectively using either RNAV SIDs or RNAV STARs, but not the other, they may still be used for this purpose in the US. If both PBN codes and NAV/RNV codes are used in the same flightplan, the NAV/RNV codes take precedence.