REQUIRED NAVIGATION PERFORMANCE
The continuing growth of aviation places increasing
demands on airspace capacity and emphasizes the need for the best use of the available airspace. These factors,
along with the accuracy of modern aviation navigation
systems and the requirement for increased operational
efficiency in terms of direct routings and track-keeping
accuracy, have resulted in the concept of required navigation
performance—a statement of the navigation
performance accuracy necessary for operation within a
defined airspace. Required Navigation Performance
(RNP) is a statement of the navigation performance
necessary for operation within a defined airspace. RNP
includes both performance and functional requirements,
and is indicated by the RNP value. The RNP
value designates the lateral performance requirement
associated with a procedure. [Figure 1-11]
RNP includes a navigation specification including
requirements for on-board performance monitoring and
alerting. These functional and performance standards
allow the flight paths of participating aircraft to be both
predictable and repeatable to the declared levels of accuracy.
More information on RNP is contained in subsequent
The term RNP is also applied as a descriptor for airspace,
routes, and procedures — including departures,
arrivals, and instrument approach procedures (IAPs).
The descriptor can apply to a unique approach procedure
or to a large region of airspace. RNP applies to navigation
performance within a designated airspace, and includes the capability of both the available infrastructure (navigation
aids) and the aircraft. Washington National Airport
(KDCA) introduced the first RNP approach procedure in
September 2005. An example of an RNP approach chart
is shown in Figure 1-12.
The RNP value designates the lateral performance
requirement associated with a procedure. The required
performance is obtained through a combination of aircraft
capability and the level of service provided by the
corresponding navigation infrastructure. From a broad
Aircraft Capability + Level of Service = Access
In this context, aircraft capability refers to the airworthiness
certification and operational approval elements
(including avionics, maintenance, database, human
factors, pilot procedures, training, and other issues).
The level of service element refers to the NAS infrastructure,
including published routes, signal-in-space
performance and availability, and air traffic management.
When considered collectively, these elements
result in providing access. Access provides the desired
benefit (airspace, procedures, routes of flight, etc.).
A key feature of RNP is the concept of on-board monitoring
and alerting. This means the navigation equipment
is accurate enough to keep the aircraft in a specific
volume of airspace, which moves along with the aircraft.
The aircraft is expected to remain within this block of
airspace for at least 95 percent of the flight time.
Additional airspace outside the 95 percent area is provided
for continuity and integrity, so that the combined
areas ensure aircraft containment 99.9 percent of the
time. RNP levels are actual distances from the centerline
of the flight path, which must be maintained for aircraft
and obstacle separation. Although additional FAA-recognized
RNP levels may be used for specific operations,
the United States currently supports three standard RNP
- RNP 0.3 – Approach
- RNP 1.0 – Terminal
- RNP 2.0 – Terminal and En Route
RNP 0.3 represents a distance of 0.3 nautical miles
(NM) either side of a specified flight path centerline.
The specific performance required on the final approach
segment of an instrument approach is an example of this
For international operations, the FAA and ICAO member
states have led initiatives to apply RNP concepts to
oceanic routes. Here are the ICAO RNP levels supported
for international operations:/p>
- RNP-1 – European Precision RNAV (P-RNAV)
- RNP-4 – Projected for oceanic/remote areas where 30 NM horizontal separation is applied
- RNP-5 – European Basic RNAV (B-RNAV)
- RNP-10 – Oceanic/remote areas where 50 NM lateral separation is applied
NOTE: Specific operational and equipment performance
requirements apply for P-RNAV and B-RNAV.