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or autopilot’s ability to control the aircraft so that its
indicated position matches the desired position. For
example, FTE increases as the CDI swings further from
center. If the cockpit instruments show the airplane to
be exactly where you want it, the FTE is essentially
zero.
Navigation System Error (NSE) is the error attributable
to the navigation system in use. It includes the navigation sensor error, receiver error, and path definition
error. NSE combines with FTE to produce the Total
System Error (TSE). TSE is the difference between
true position of the aircraft and the desired position.
It combines the flight technical errors and the navigation system tracking errors.
Actual navigation performance (ANP) is an estimate of
confidence in the current navigation system’s performance. ANP computations consider accuracy, availability, continuity, and integrity of navigation performance
at a given moment in time. Required Navigation
Performance (RNP) necessitates the aircraft navigation
system monitor the ANP and ensures the ANP does not
exceed the RNP value required for the operation. The
navigation system must also provide the pilot an alert
in the primary field of view when ANP exceeds RNP.
[Figure B-3 on page B-4]
While you may have thought of protected airspace as
static and existing at all times whether aircraft are present or not, protection from conflicts with other aircraft
is dynamic and constantly changing as aircraft move
through the airspace. With continuous increases in air
traffic, some routes have become extremely congested.
Fortunately, the accuracy and integrity of aircraft navigation systems has also increased, making it possible to
reduce the separation between aircraft routes without
compromising safety. RNP is a standard for the navigation performance necessary to accurately keep an
aircraft within a specific block of airspace.
Containment is a term central to the basic concept of
RNP. This is the idea that the aircraft will remain within
a certain distance of its intended position (the stated
RNP value) at least 95 percent of the time on any flight.
The FDA is smallest when
the NAVAIDs are close to
the fix and the angle
defining the fix is
90 degrees.
At greater distances
from the NAVAIDs,
the FDA is larger.
At less favorable angles,
the FDA is larger.
Fix Displacement Area (FDA)
Facility
Facility
Facility
Figure B-2. The size of the protected airspace depends on where the terrestrial NAVAIDs that define it are located.
B-4
This is a very high percentage, but it would
not be enough to ensure the required level of
safety without another layer of protection outside the basic containment area. This larger
area has dimensions that are twice the RNP
value, giving the aircraft two times the lateral
area of the primary RNP area. Aircraft are
expected to be contained within this larger
boundary 99.999 percent of the time, which
achieves the required level of confidence for
safety. [Figure B-4]
Figure B-5 on pages B-6 through B-9 helps
explain the cockpit indications and tolerances that will comply with criteria to keep
you within protected airspace. The tolerances are predicated on zero instrument error
unless noted otherwise. Special Aircraft and
Figure B-3. An alerting system in the pilot’s primary view must warn if ANP
exceeds RNP. This alerting system is comparable to an “OFF” flag for a VOR
or ILS.
Twice RNP Value
RNP Value
Aircraft must remain
within this area 95
percent of the flight.
Aircraft remains within this
area 99.999 percent of the time.
Figure B-4. RNP Containment.
B-5
Aircrew Authorization Required (SAAAR) routes are
not covered in this table.
For approaches, it is not enough to just stay within protected airspace. For nonprecision approaches, you must
also establish a rate of descent and a track that will
ensure arrival at the MDA prior to reaching the MAP
with the aircraft continuously in a position from which a
descent to a landing on the intended runway can be made
at a normal rate using normal maneuvers. For precision
approaches or approaches with vertical guidance, a transition to a normal landing is made only when the aircraft
is in a position from which a descent to a landing on the
runway can be made at a normal rate of descent using
normal maneuvering.
For a pilot, remaining within protected airspace is
largely a matter of staying as close as possible to the
centerline of the intended course. There are formal definitions of what it means to be established on course, and
　
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