RNAV/RNP Operations & VNAV Approaches

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Captain Bill Royce
Senior Technical Pilot
Flight Operations Training, Technical & Standards
Boeing Commercial Airplanes
RNAV/RNP Operations &
VNAV Approaches
The Boeing Company W100.2
Discussion Objectives
• Discuss current RNAV status – US and Europe
• Provide safety-related background information
• Provide an understanding of basic RNP/ANP
concepts and operations
• Provide an understanding of VNAV approach
selection, execution and related topics
The Boeing Company W100.3
RNAV Use is Growing…
• We are now seeing a gradual transition from groundbased
navigation aids to satellite based navigation
• More routes and procedures with no underlying
navigation aids are being published
• RNAV capabilities are now being exploited further by US,
European and other air traffic service providers
– RNP operations
– Increased traffic capacity en-route
– SIDs, STARs and approaches
• Operators taking advantage of RNP operations
– Improved airport access; lower minima
– Increased safety; less reliance on VOR/ADF
– Increased payloads from special procedures
The Boeing Company W100.4
RNP/RNAV = Higher Payload
Example:
• Hong Kong (departing RW07)
• Weight limit governed by distant obstacle
• Engine-out SID developed with immediate turn after
takeoff (RNP 0.15)
• Payload increased by several tonnes
The Boeing Company W100.5
Current US RNAV Status
• Use of RNAV widespread and growing
• Many RNAV and GPS approaches
• Lower VNAV minima available
• GPS approaches being re-designated as RNAV
• RNP 1.0 SIDs and STARs available and increasing
in number
• Some special procedures developed (as low as
RNP 0.11)
The Boeing Company W100.6
RNAV – VNAV examples
The Boeing Company W100.7
Current Euro-control RNAV Status
• BRNAV (RNP 5.0) established for airways
• PRNAV (RNP 1.0) is implemented for terminal
operations (before FAF) – TGL 10 published.
• Requirements for Baro-VNAV and RNAV/RNP
approaches being established – TGLs being drafted
• Some RNAV approaches available
The Boeing Company W100.8
Safety History of Non-ILS
Approaches Suggests RNAV/RNP
• 60% of CFIT accidents occur on NP approaches
• 47% occurred during step-down NP approaches
• Almost all accidents occurred in darkness or IMC
• 48% in mostly flat terrain
• Most common cause: descent below MDA
The Boeing Company W100.9
Map Location of Recent CFIT
Accidents/Incidents
The Boeing Company W100.10
Vertical Profile of Recent CFIT
Accidents/Incidents
The Boeing Company W100.11
RNP/ANP Operations
• Definitions
• Why RNP?
• RNP vs ANP
• Airplane capability
• RNP/ANP displays and entries
• Crew Alerting summary
The Boeing Company W100.12
Definitions
• RNP – Required Navigation Performance.
– Specified navigation accuracy for a route or
departure/approach procedure in NM units
– Enroute RNPs usually 2.0 or greater
– Approach RNPs can be as low as 0.11
• ANP – Actual Navigation Performance
– The FMC calculated certainty of the airplane’s
position in NM units
– There is a 95% probability that the airplane is
within the displayed ANP
The Boeing Company W100.13
Why RNP?
• Required Navigation Performance, or RNP, was
developed as a method for certifying the navigation
certainty for RNAV systems that can use multiple
sensors for position updating
• RNP is used as a criteria for design of terminal area
procedures and en-route segments
• RNP relates to obstacle clearance and/or traffic
separation criteria
The Boeing Company W100.14
Factors Influencing ANP
• Method of FMC position updating (GPS, DME-DME,
etc)
• GPS Receiver Autonomous Integrity Monitoring
(RAIM) – only when using GPS updating
• If using navigation radio updating, geometry and
proximity of stations to airplane position
• Time since last radio or GPS update (for the 737,
without updating the ANP gradually increases)
The Boeing Company W100.15
ANP - a Measure of Position
Certainty and Route Containment
FMC position
ANP
95% Probability
(NM)
2xRNP 2xRNP
RNAV route
The Boeing Company W100.16
What FMCs Have RNP Capability?
• 737-3/4/500 FMC U7.1 or later
• 737-6/7/8/900/BBJ All
• 747-400 FANS (FMC Load 11 or later)
• 757/767 Pegasus
• 777 All
[All FMCs that show RNP/ANP]
The Boeing Company W100.17
FMC-provided RNPs
• The FMC provides the RNP for the current route
segment or terminal area procedure from the navigation
data base if available
• If no RNP is available from the navigation data base, the
FMC provides a default value according to the current
phase of navigation:
– Approach 0.5 or 0.3 NM
– Terminal (below 15,000’) 1.0 NM
– En-route (domestic) 2.0 NM
– Oceanic 12.0 NM
• The operator may select different default values
• If no RNP is specified for a route segment or terminal
area procedure, the FMC default value is normally
acceptable
The Boeing Company W100.18
Procedure or Route-Specific RNPs
are Indicated on Charts
The Boeing Company W100.19
Procedure or Route-Specific RNPs
are Indicated on Charts
The Boeing Company W100.20
RNP for GPS Approaches
• GPS approaches can be flown with RNP-capable
FMCs
• GPS updating may also be required
• RNP 0.3 must be used and is normally manually
entered prior to commencing the approach
• Some operators have selected RNP 0.3 as the
approach default value to eliminate the need to
make this entry
The Boeing Company W100.21
More About RNP & ANP
• ANP does not relate to course tracking accuracy!
• When ANP exceeds RNP the airplane position accuracy is
in question
• Smaller RNPs require more accurate FMC updating sources
(DME-DME, GPS, etc)
• When ANP exceeds RNP, the airplane’s actual navigation
position does not meet the required accuracy and a crew
alert is provided
The Boeing Company W100.22
Crew Alerting Occurs When ANP
Exceeds RNP
• 757/67/77/47 – Caution level EICAS alert message during
the approach phase, advisory level at other times
– 777: NAV UNABLE RNP
– 757/767: UNABLE RNP
– 747-400: UNABLE RNP
• 737: UNABLE REQD NAV PERF-RNP displayed on
Navigation Display during the approach phase, FMC
scratchpad message at other times
• 737: Loss of GPS updating may not result in an RNP alert
for some period of time since the ANP will change gradually.
The Boeing Company W100.23
Course Tracking Accuracy
• Observe the relationship of the airplane symbol and track
line to the FMC course on the map display, and
• Observe the cross-track error on the FMC PROGRESS
page 2
• Use of the autopilot in LNAV is normally the best method
to ensure proper course tracking!
The Boeing Company W100.24
Response to an UNABLE RNP Alert
• Verify position using radar or other available
navaids
• If on an RNP route segment or RNP terminal area
procedure:
– Notify ATC immediately
– Make an immediate missed approach if on an
RNP approach
– Request an amended (non-RNP) clearance
• If on the ground, a realignment is needed
The Boeing Company W100.25
VERIFY RNP FMC Message
• This message occurs to alert the crew that the
manual RNP entry exceeds the default RNP or the
RNP from the navigation data base, if available
• The crew must confirm the RNP entry
• If required, delete the manually entered RNP to use
the FMC default value or the RNP from the
navigation data base, if available
The Boeing Company W100.26
VNAV Approach Topics
• Types of approaches that are VNAV compatible
• Types of approaches that are not VNAV compatible
• Use of Decision Altitudes (DA(H)) versus Minimum
Descent Altitudes (MDA(H))
• VNAV-related changes to charted approaches and
navigation data bases
• FMC “on-approach” logic
• Flying the approach
• Other approach-related topics
The Boeing Company W100.27
Types of Approaches that are
VNAV Compatible
• Non-ILS approach procedures such as RNAV, GPS,
VOR, NDB, LOC, LOC-BC, SDF, etc. that have one
or more of the following:
– An appropriate path that has a missed approach
point at or before the runway threshold
– There is a glide path (GP) angle indicated on the
chart and/or shown on the legs page
– Approaches with a published VNAV DA(H)
Note: Many approaches are coded with a GP angle
which the charted Jeppesen procedure does not
show
The Boeing Company W100.28
On the LEGS Page, a VNAVCompatible
Path Will Have:
• An RWxx or MXxx waypoint at or before the
approach end of the runway
– The waypoint altitude constraint will result in
approximately 50 feet threshold crossing height
(TCH)
– Examples (runway 12, TDZE at 1000’ MSL)
–RW12 170/1050
– MA12 170/1190
• A “GP” angle shown on the LEGS page for the final
approach segment
The Boeing Company W100.29
FMC Legs Page Shows
Glide Path Angle
The Boeing Company W100.30
Approach Diagram Shows G.P.
Angle and VNAV Compatibility
The Boeing Company W100.31
VNAV DA(H)s also show VNAV
compatibility
The Boeing Company W100.32
Types of Approaches That Are Not
VNAV-Compatible
• Approaches that do not have a GP angle, and
• There is no RWxx or MXxx waypoint with an
appropriate path terminating at approximately 50’
above the runway threshold, or
• The missed approach point is beyond the runway
threshold
The Boeing Company W100.33
FAA AC 120-29A Contains
Guidance on Use of VNAV
• VNAV approaches are considered as a “Category I Approach”
with a decision altitude (DA(H))
• VOR, VOR/DME, NDB, LOC or LOC BC approaches may be
flown with DA(H)s not less than 250 feet using VNAV, with
appropriate operational approval and equipment
• A DA (QNH barometric altitude) is used
• Use of a published VNAV path, or GP angle, is required when
a DA(H) is used
The Boeing Company W100.34
FAA HBAT 99-08 Permits Use of
MDA(H)s as DA(H)s
• Eligible procedures include: VOR, VOR/DME, NDB,
RNAV, GPS, LOC, LOC-BC, LDA and SDF
• When VNAV PTH is used, a slight momentary
descent below the published DA(H) during the
missed approach is acceptable
• RNP 0.3 capability or less is required
• Eligible procedures must have a visual segment
obstacle assessment
• Without a published DA(H), the MDA(H) may be
used as a DA(H) (with operational approval)
The Boeing Company W100.35
FAA Visual Segment Obstacle
Assessment Complete for:
• ILS approaches with a published GP angle
• Runways with a VASI or PAPI
• RNAV approaches with a published VNAV DA (H)
The Boeing Company W100.36
The GP Angle Provides Obstacle
Clearance
• A published GP angle is evidence that:
– the VNAV path will arrive at the published TCH, and
– complies with underlying step-down altitudes
• The GP angle is constructed “backward” from the 50’
runway waypoint and normally intersects the FAF altitude
constraint
50 ft.
RW12
FAF
3.00
The Boeing Company W100.37
The GP Angle Complies with the
Step-down Altitudes
The Boeing Company W100.38
Most GP Angles Have a “Fly-off”
• If the distance from the FAF to the runway is greater
than required for an immediate descent
• The “fly-off” may be indicated on the chart. Some
FMCs (737 only) provide a “T/D” on the map display
at the end of the “fly-off.”
• The FMC will command level flight in VNAV PTH
until reaching the descent path
The Boeing Company W100.39
GP “Flyoff” Example
The Boeing Company W100.40
Non-ILS VNAV Path Availability:
Total vs.% Flyable in VNAV
• Europe 1028/93%
• Africa 330/87%
• S. America 337/56%
• Middle East 468/87%
• USA 4400/90%
• Canada 657/90%
• Asia/Pacific 639/90%
•Based on an informal navigation data base survey
•Jeppesen is in the process of recoding all non-ILS
approaches
The Boeing Company W100.41
Typical VNAV Approach
Procedure (except 737-3/4/500)
Prior to approach
• Select approach procedure
• Verify/enter RNP
Final descent and at least 300’ below MAP Altitude
• Set missed approach altitude
At DA (or MDA + 50 feet)
• Disengage Autopilot/Autothrottle
or
• Go-Around
Approx 2 NM prior to FAF
• Set MDA/DA
• Verify/select roll mode (LNAV, or other)
• Select VNAV (VNAV PTH) & speed intervention
• Autopilot engaged
((RRWWXXXX oorr MMXXXXXX))
((FFAAFF))
The Boeing Company W100.42
Typical VNAV Approach
Procedure (737-3/4/500, U7.1 or later)
Prior to approach
• Select approach procedure
• Verify/enter RNP
Approaching MDA/DA
• Set missed approach altitude
• Disengage Autopilot/Autothrottle
At DA (or MDA + 50 feet)
• Continue to landing
or
• Go-Around
Approx 2 NM prior to FAF
• Set MDA/DA
• Verify/select roll mode (LNAV, or other)
• Select VNAV (VNAV PTH) & speed intervention
• Autopilot engaged
((RRWWXXXX oorr MMXXXXXX))
((FFAAFF))
The Boeing Company W100.43
Recommended Procedure if Use of
DA(H) Not Approved
• Set MDA(H) + 50’ using the minimums selector
• Use the same procedure as previously discussed
• Initiate the missed approach at MDA(H) + 50’ if
adequate visual reference is not established
The Boeing Company W100.44
Approach Example
RNP &
other info
VNAV
minimums
GP angle
The Boeing Company W100.45
Autopilot Use
• Autopilot use is recommended on VNAV
approaches
• Experience has shown autopilot use on non-ILS
approaches to be beneficial
• Better vertical and lateral path tracking
• Lower workload
• Less possibility of below path excursions
The Boeing Company W100.46
AFDS Mode Reversions from
VNAV PTH (747-400/757/767/777)
• The 747-400, 757/767 and 777 AFDS, once in
VNAV PTH and on approach, will not revert to any
other mode automatically except to climb above the
path in VNAV SPD if the placard speed is
approached
• VNAV PTH mode must be exited by another mode
selection or via go-around initiation
• With the AFDS engaged, the airplane will stay on
path
The Boeing Company W100.47
AFDS Mode Reversions from
VNAV PTH (737)
• The 737NG AFDS, once in VNAV PTH and on
approach, will not revert to any other mode with
landing flaps selected
• VNAV PTH mode must be exited by another mode
selection or via go-around initiation
• With the AFDS engaged, the airplane will stay on
path
Note: Earlier NG FCCs and all 737-3/4/500 FCCs
permit the AFDS to automatically revert to LVL CHG
if a significant under-speed occurs (alpha mode).
The Boeing Company W100.48
Raw Data Monitoring
• For all types of approaches that are based on
ground navigation aids raw data should be
monitored if available
• A raw data check prior to final approach may be
accomplished by:
– Using the POS function on the 737NG, 747-400,
767-400 and 777
– Using the VOR/ADF function on the 737-3/4/500
• The 757/767 still require a VOR deviation display for
VOR approaches on final approach
The Boeing Company W100.49
POS Function – FMC Position is
Verified if Raw Data Matches Map
R-200
R-120
DME raw data
GPS position
The Boeing Company W100.50
“On-Approach” Logic
• Criteria met for all airplanes using the published Boeing
VNAV procedure
• Raises the alerting level to Caution for UNABLE RNP
• Causes the RNP to change to approach RNP if not
manually entered
• Permits selection of the missed approach altitude and
continued descent in VNAV PTH (except 737 classic)
• Speed intervention is enabled in VNAV PTH mode
• For VOR approaches, the FMC auto-tunes the VOR and
automatically inserts the final approach course on the
NAV RAD page and on the navigation display
The Boeing Company W100.51
Waypoint Modifications for VNAV
Approaches
• Approach waypoints should normally be used “as is” from
the navigation data base
• Use of a VNAV DA(H) requires use of a GP angle
• A straight-in intercept course to the FAF is permissible for
radar vectored approaches
• Appropriate cold temperature corrections to waypoint
altitude constraints are permissible
• Do not add or delete waypoints in the final approach
segment!
The Boeing Company W100.52
Pilot-Constructed Approaches
• Navigation data base selection is required for RNAV and
GPS approaches
• Approaches from the navigation data base are preferred for
other types of approaches
• If no navigation data base approach is available and time
permits, a manually constructed approach may be flown
using LNAV provided:
– Navigation data base waypoints and the RW waypoint are
used
– VOR, DME or other raw data is used as the primary
navigation reference for the approach
The Boeing Company W100.53
Pilot-constructed approaches, cont.
• VNAV (using speed intervention) would be available
only if using an overlay approach such as an ILS
when flying an NDB approach and the waypoint
altitude constraints were modified to comply with the
approach to be flown
• Manually constructed waypoints are not compatible
with on-approach logic
• Automatic procedure tuning will not occur for pilotconstructed
approaches (747-400, 767-400 and 777
only)
The Boeing Company W100.54
Operations in Non-WGS-84
Airspace
• SIDs, STARs and enroute navigation are OK with
GPS updating active
• GPS need not be turned off if “appropriate
procedures are used”
• RNAV approaches may be flown with GPS active
only if appropriately verified in the non-WGS-84
environment
• VOR or ADF approaches may be flown using LNAV
with GPS active if raw data monitoring is used
throughout the approach
The Boeing Company W100.55
Cold and Warm Temperature
Considerations
• The VNAV path coincides with the published angle only when the
temperature is ISA (standard). It will be:
– Steeper in warmer temperatures
– Shallower in colder temperatures
• Some approaches have a published minimum temperature
• In extreme cold temperatures, when appropriate, the pilot should
consider adding a cold temperature altitude correction to the FAF
and approach transition waypoint constraints to correct the path
• The altimeter error will be greater near the FAF and smaller near
the runway
The Boeing Company W100.56
The VNAV Path Is Affected By
Temperature
50 ft.
RW12
FAF
3.00
Warmer than ISA
Standard day (ISA)
Correction Colder than ISA
The Boeing Company W100.57
System failures
• With dual navigation systems most single navigation system
failures will not result in an UNABLE RNP alert or otherwise
prevent an approach from being flown
• Loss of a single FMC or GPS receiver will not affect ANP
• If operating with a single updating sensor (such as GPS or DME if
GPS is not being used) or a single FMC there must be a non-
FMC means of navigation available for the approach and missed
approach:
– Radar vectors, or
– VOR, or
– NDB, etc.
The Boeing Company W100.58
RNAV with Non-GPS Airplanes
• Without GPS updating the FMC meets accuracy requirements for
en-route and terminal area navigation (RNP 2.0 and 1.0)
assuming DME-DME updating is active
• The 777/747/757/767 (both GPS failed) satisfies RNP 10
assuming max time from last DME update less than 6 hours
• For approaches, including RNAV, RNP 0.5 capability exists but
DME-DME updating must be confirmed by the crew prior to
starting the approach
• RNP display capability is not required provided approach RNP is
0.5 or greater
• GPS approaches at US airports require GPS updating to be
active (D-D updating not allowed for RNP 0.3)
The Boeing Company W100.59
Summary
• RNAV/RNP operations can be a significant operational
advantage to most airlines
– Increased payload by creative procedure design
– More reliable airport access thru lower minima
– Possibility to eliminate ‘problem’ approaches
• LNAV/VNAV PTH operations are becoming the best way to
conduct non-ILS operations
– Better control of lateral and vertical path
– Lower minima
– Lower workload; easier to fly & stabilize

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