The operational advantages of RNP include accuracy
and integrity monitoring, which provide more precision
and lower minimums than conventional RNAV.
RNP DAs can be as low as 250 feet with visibilities as
low as 3/4 SM. Besides lower minimums, the benefits
of RNP include improved obstacle clearance limits, as
well as reduced pilot workload. When RNP-capable
aircraft fly an accurate, repeatable path, ATC can be
confident that these aircraft will be at a specific position,
thus maximizing safety and increasing capacity.
To attain the benefits of RNP approach procedures, a
key component is curved flight tracks. Constant radius
turns around a fix are called “radius-to-fix legs,” or RF
legs. These turns, which are encoded into the navigation
database, allow the aircraft to avoid critical areas
of terrain or conflicting airspace while preserving positional
accuracy by maintaining precise, positive course
guidance along the curved track. The introduction of
RF legs into the design of terminal RNAV procedures
results in improved use of airspace and allows procedures
to be developed to and from runways that are otherwise
limited to traditional linear flight paths or, in
some cases, not served by an IFR procedure at all.
Navigation systems with RF capability are a prerequisite
to flying a procedure that includes an RF leg. Refer
to the notes box of the pilot briefing portion of the
approach chart in figure 5-17.
In the United States, all RNP procedures are in the category
of Special Aircraft and Aircrew Authorization
Required (SAAAR). Operators who seek to take advantage
of RNP approach procedures must meet the special
RNP requirements outlined in FAA AC 90-101,
Approval Guidance for RNP Procedures with SAAAR.
Currently, most new transport category airplanes
receive an airworthiness approval for RNP operations.
However, differences can exist in the level of precision
that each system is qualified to meet. Each individual
operator is responsible for obtaining the necessary
approval and authorization to use these instrument
flight procedures with navigation databases.
RNAV APPROACH AUTHORIZATION
Like any other authorization given to air carriers and Part
91 operators, the authorization to use VNAV on a conventional
nonprecision approach, RNAV approaches, or
LNAV/VNAV approaches is found in that operator’s
OpsSpecs, AFM, or other FAA-approved documents.
There are many different levels of authorizations when
it comes to the use of RNAV approach systems. The
type of equipment installed in the aircraft, the redundancy
of that equipment, its operational status, the level
of flight crew training, and the level of the operator’s
FAA authorization are all factors that can affect a
pilot’s ability to use VNAV information on an
Because most Part 121, 125, 135, and 91 flight departments
include RNAV approach information in their
pilot training programs, a flight crew considering an
approach to North Platte, Nebraska, using the RNAV
(GPS) RWY 30 approach shown in figure 5-18, would
already know which minimums they were authorized
to use. The company’s OpsSpecs, Flight Operations
Manual, and the AFM for the pilot’s aircraft would
dictate the specific operational conditions and
procedures by which this type of approach could
There are several items of note that are specific to this
type of approach that should be considered and briefed.
One is the terminal arrival area (TAA) that is displayed
in the approach planview. TAAs, discussed later
in this chapter, depict the boundaries of specific arrival
areas, and the MIA for those areas. The TAAs should
be included in an IAP briefing in the same manner as
any other IFR transition altitude. It is also important to
note that the altitudes listed in the TAAs should be
referenced in place of the MSAs on the approach
chart for use in emergency situations.
In addition to the obvious differences contained in the
planview of the previous RNAV (GPS) approach procedure
example, pilots should be aware of the issues
related to Baro-VNAV and RNP. The notes section of
the procedure in the example contains restrictions
relating to these topics.
Figure 5-17. RNAV (RNP) Approach Procedure with Curved Flight Tracks.
Figure 5-18. North Platte Regional (KLBF), North Platte, Nebraska, RNAV (GPS) RWY 30.
Baro-VNAV avionics provide advisory VNAV path
indications to the pilot referencing a procedure’s
vertical path angle (VPA). The computer calculated
vertical guidance is based on barometric altitude,
and is either computed as a geometric path between
two waypoints or an angle from a single waypoint. If
a flight crew is authorized to conduct VNAV
approaches using an RNAV system that falls into this
category, the Baro-VNAV temperature limitations
listed in the notes section of the approach procedure
apply. Also, since Baro-VNAV is advisory guidance,
the pilot must continuously crosscheck the primary
barometric altimeter to ensure compliance with all
altitude restrictions on an instrument procedure.
Considering the pronounced effect of cold temperatures
on Baro-VNAV operations, a minimum
temperature limitation is published for each
procedure for which Baro-VNAV minimums are
published. This temperature represents the airport
temperature below which the use of Baro-VNAV
is not authorized to the LNAV/VNAV DA. The
note “Baro-VNAV NA below -20°C (-4°F)”
implies that the approach may not be flown at all
using Baro-VNAV when the temperature is below
-20° Celsius. However, Baro-VNAV may be used
for approach guidance down to the published
LNAV MDA. This information can be seen in the
notes section of the previous example.
In the example for the RNAV (GPS) RWY 30
approach, the note “DME/DME RNP-0.3 NA” prohibits
aircraft that use only DME/DME sensors for
RNAV from conducting the approach.
Because these procedures can be flown with an
approach approved RNP system and “RNP” is not sensor
specific, it was necessary to add this note to make it
clear that those aircraft deriving RNP 0.3 using
DME/DME only are not authorized to conduct the procedure.
The lowest performing sensor authorized for RNP navigation
is DME/DME. The necessary DME NAVAID
ground infrastructure may or may not be available at
the airport of intended landing. The procedure designer
has a computer program for determining the usability
of DME based on geometry and coverage. Where FAA
Flight Inspection successfully determines that the coverage
and accuracy of DME facilities support RNP, and
that the DME signal meets inspection tolerances,
although there are none currently published, the note
“DME/DME RNP 0.3 Authorized” would be charted.
Where DME facility availability is a factor, the note
would read, “DME/DME RNP 0.3 Authorized; ABC
and XYZ required,” meaning that ABC and XYZ DME
facilities are required to assure RNP 0.3.