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
737 Flight Crew Training Manual
.
intercept course to or direct to route modifications delete an RF leg if
done to the second waypoint on an RF leg
.
RF legs are not preserved in the event of an FMC failure. They become
route discontinuities
737-300 - 737-500
.
if a go-around is executed while on an RF leg, it is important to
immediately re-select LNAV to avoid excessive course deviation. GA roll
mode is a track hold mode and is not compatible with low RNP operations
if left engaged. The pilot flying must continue to track the LNAV course
using the map display as a reference until LNAV is re-engaged.
737-600 - 737-900
.
if a go-around is executed while on an RF leg, it is important to verify
LNAV has re-engaged to avoid excessive course deviation. GA roll mode
is a track hold mode and is not compatible with low RNP operations if left
engaged. The pilot flying must continue to track the LNAV course using
the map display as a reference until LNAV is re-engaged.
RNAV Operations: En-route, Terminal, and Approach
All Boeing FMCs are capable of performing RNAV operations. Regarding navigation accuracy, these FMCs differ only by demonstrated RNP capabilities and the ability to use GPS updating.
En-route operations can be defined as oceanic and domestic. Oceanic RNAV requirements are described in detail in the applicable MNPS guidance material such as the Pacific or North Atlantic manuals. Specific routes or areas of operation are given RNPs based on route separation requirements. RNP 10 routes are suitable for all FMCs that are capable of GPS updating and those FMCs that cannot update from GPS but have received the last radio update within the previous six hours.
In general, oceanic operations require dual navigation systems (dual FMC or single FMC in combination with alternate navigation capability).
Domestic en-route RNAV operations depend on the availability of radio updating (DME-DME) sources to support domestic RNPs. The following domestic RNP operations are fully supported by any Boeing FMC with DME-DME or GPS updating active:
.
USA and Canada - RNP 2.0 or higher
.
Europe - B-RNAV (RNP 5.0)
.
Asia - As specified for the route or area (e.g. RNP 4 or RNP 10 routes)
.
Africa - As specified for the route or area
Terminal RNAV operations (SIDs, STARs and Transitions) are fully compatible with all FMCs with DME-DME or GPS updating active and are defined as:
.
USA and Canada - RNP 1.0 SIDs and STARS
.
Europe - P-RNAV (RNP 1.0).
Copyright . The Boeing Company. See title page for details.
1.48 FCT 737 (TM) October 31, 2006
737 Flight Crew Training Manual
RNAV approaches are compatible with all FMCs provided DME-DME or GPS updating is active at the beginning of the approach and the approach RNP is equal to or greater than the minimum demonstrated RNP in the AFM. Restrictions published on some RNAV approaches may preclude their use without GPS updating active.
For published RNAV approaches, all Boeing FMCs have RNP 0.5 capability with DME-DME updating active without GPS updating. See the Approach section of this manual for further details regarding the techniques for flying RNAV approaches.
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