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the procedure, airspace, or route, may cause nuisance crew alerts. If the RNP is set
larger than that specified for a procedure or segment, crew alerting may occur at
the incorrect RNP (if the specified RNP is exceeded). Operators should select
FMC default values that meet the requirements of their route structure or terminal
area procedures. However, AFM requirements may specify RNPs for certain
approaches. (For example, RNP 0.3 is required for RNAV (GPS) approaches).
The FMC calculates and displays its Actual Navigation Performance (ANP) as
described in the FCOM. When the ANP exceeds the RNP a crew alert is provided.
When this occurs on a route or terminal area procedure where an RNP is
published, the crew should verify position, confirm updating is enabled, and
consider requesting an alternate clearance. This may mean changing to a non-RNP
procedure or route or changing to a procedure or route with a RNP higher than the
displayed ANP value. Crews should note that ANP is only related to the accuracy
of FMC position. Lateral deviation from the route or procedural track is indicated
by the XTK ERROR (cross-track error) value shown by the FMC. LNAV is
required for all RNP operations. Use of the autopilot is recommended to minimize
cross-track error. An excessive cross-track error does not result in a crew alert.
October 31, 2006
777/787 Flight Crew Training Manual
General Information
Copyright © The Boeing Company. See title page for details.
FCT 777/787 Preliminary (TM) 1.35
777-200 - 777-300ER
Note: The NPS system (as installed) provides an alert on the PFD when lateral or
vertical deviation exceeds preset limits. Reference the FCOM for specific
NPS system indications and description.
The following illustration shows the FMC position and displayed ANP and shows
the relationship of ANP to RNP for a particular route segment. Normally, a route
segment or procedural leg is defined by its required width (the illustration shows
2.0 NM either side of the centerline). RNP is normally set at 50% of the allowed
maximum deviation from the route centerline. Required width is determined by
minimum terrain or traffic clearance requirements. The probability of exceeding
this maximum deviation while in LNAV with the autopilot engaged is very small.
For each airplane type, minimum demonstrated RNPs are given in the AFM.
These minimum values vary depending on LNAV, flight director and autopilot
use, and whether GPS is the active source of position updating.
Low RNP operations such as RNP 0.15 and below require precise path tracking.
Use of the autopilot and LNAV normally provide the required path tracking
accuracy. Some RNAV (RNP) approach procedures also require use of VNAV
PTH for vertical guidance. These procedures show only LNAV/VNAV approach
minima and do not allow use of LNAV only. Use of the flight director alone may
not provide sufficient guidance to maintain the path accurately.
787-8
Note: If the autopilot is not available, flight crews should use the flight director
and the additional cues displayed on the navigation display (position trend
vector, airplane symbol, and digital cross track deviation) with at least one
map set at a range of 10 NM or less.
777-200 - 777-300ER
Note: If the autopilot is not available, flight crews should use the flight director
and the additional cues displayed on the navigation display (position trend
vector, airplane symbol, and digital cross track deviation) with at least one
map set at the 10 NM range.
October 31, 2006
777/787 Flight Crew Training Manual
General Information
Copyright © The Boeing Company. See title page for details.
1.36 FCT 777/787 Preliminary (TM)
RNAV Route and RNP/ANP
Radius-to-Fix RF Legs
RF legs are waypoints connected by a constant radius course similar to a DME arc.
These are shown on terminal procedures as a curved track between two or more
waypoints. Some considerations regarding use of RF legs:
• there may be a maximum speed shown on some RF legs of smaller radius.
This limitation is critical for the crew to observe since the ability of the
AFDS to track the RF leg is determined by ground speed and maximum
available bank angle. In high winds, the maximum bank angle may be
reached, causing excessive course deviation if the maximum speed is
exceeded
• do not begin a procedure by proceeding direct to an RF leg. This may
cause excessive deviation when the airplane maneuvers to join the RF leg.
Normally there is a track-to-fix leg prior to an RF leg to ensure proper RF
leg tracking
ANP
RNP
(1.0 NM example)
FMC
Position
Required Route Width
　
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