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inaccurate. FMC predictions for the climb and descent path are not usable.
Do not use FMC fuel predictions. Cruise fuel predictions are based on a clean
configuration. Fuel consumption may be significantly higher than predicted in
other configurations.
Note: VNAV PTH operation for approaches is usable for non-normal
configurations.
An accurate estimated time of arrival is available if current speed or Mach is
entered into the VNAV cruise page. Estimates of fuel remaining at waypoints or
the destination may be computed by the crew based upon current fuel flow
indications, but should be updated frequently. Performance information for gear
down altitude capability and gear down cruise performance is available in the PI
chapter of the QRH.
Holding time available is accurate in the clean and flaps one configuration
provided the FMC holding speed is maintained.
RNP and RNAV Operations
This section describes the basic concepts of RNP and provides information on
RNAV operations by phase of flight to include terminal (SIDs and STARs),
en-route, and approach.
Basic RNP Concept
RNP has been developed through international cooperation as a means of
identifying the navigation performance required for a specified area, route,
airspace, procedure or operation. RNP supports use of RNAV systems that use
multi-sensor position updating methods such as the flight management computer
(FMC). This accuracy is specified in NM (e.g., RNP 0.3 means the performance
required is “within 0.3 NM”). RNP values are usually smaller for terminal area
procedures (SIDs, STARs, approach transitions, and approaches) than en-route
procedures. Small RNP values normally require navigation performance that is
more precise than current VOR/ADF navigation, allowing lower weather minima
for departures and/or approaches.
October 31, 2004
767 Flight Crew Training Manual
General Information
Copyright © The Boeing Company. See title page for details.
1.32 FCT 767 (TM)
The FMC uses one of the following as the displayed RNP:
• default RNP - FMC default values are set by the FMC and are displayed if
no RNP is available from the navigation data base or one has not been
manually entered
• navigation Data Base RNP - RNP values (if available) are displayed
based on values associated with the procedure. These values may be
unique for certain segments or terminal procedures
• manually entered RNP - remains until changed or deleted.
The crew may need to make a manual RNP entry if the displayed RNP for the
route or procedure is incorrect. Setting an RNP smaller than what is specified for
the procedure, airspace, or route, may cause nuisance crew alerts. If the RNP is
larger than required for a procedure or segment, inadequate alerting results if
needed. 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 should
be used with the autopilot engaged to minimize cross-track error. Excessive XTK
ERROR does not result in a crew alert.
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.
October 31, 2004
767 Flight Crew Training Manual
General Information
　
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