Alternative Obstacle Clearance Criteria for RNP RNAV Instrument Approaches

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© 2004 The MITRE Corporation. All Rights Reserved.
Alternative Obstacle Clearance Criteria for
RNP RNAV Instrument Approaches
S.V. “Vince” Massimini, DSc
Frederick A. Niles
April 2004
2
April 2004
© 2004 The MITRE Corporation. All Rights Reserved.
Obstacle Clearance Surfaces (OCSs)
Instrument Landing System (ILS)
3
April 2004
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OCSs for ILS
4
April 2004
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Vertical OCSs
Not to Scale
200'
Touchdown Elevation
-
954' 2,379' 1,237' 7,983'
3 Glide slope o
185' HAT
250' HAT
668' HAT
954' 1,154' 3,533' 4,770' 12,753'
34:1 ILS/GLS
5
April 2004
© 2004 The MITRE Corporation. All Rights Reserved.
Determining Visibility Minima
HAT = 326 ft
Glide Slope = 3º
Threshold Crossing Height = 50 ft
954 ft 5280 ft = 1 sm
3960 ft=3/4 sm
HAT = 257 ft
1. Determine Height Above Touchdown (HAT) from OCS
2. Determine visibility from distance of HAT point to runway threshold
3. Approach lights can affect visibility
Not to Scale
6
April 2004
© 2004 The MITRE Corporation. All Rights Reserved.
Wide Area Augmentation System (WAAS)
GPS Satellites
Communication Satellite
(with WAAS transponder)
Ground Earth
Stations
Wide Area
Master Station
Wide Area
Reference Station
GPS
WAAS
Correction
Terms,
Integrity Data
GPS-Like
Signals
7
April 2004
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Local Area Augmentation System (LAAS)
Global Positioning System
VHF Data Broadcast
LAAS Differential Receiver Stations
Correction Terms, Integrity Data
LAAS Differential Transmitter Station
GPS Satellites
GPS Satellites
Surveyed
Antenna
All elements sited on airport property
Local Area
Augmentation System
GPS/LAAS
User Equipment
8
April 2004
© 2004 The MITRE Corporation. All Rights Reserved.
GPS/WAAS/LAAS Approaches
Area Navigation (RNAV) Approaches
• WAAS intent has been to provide several levels of service for instrument
approaches
– Lateral Navigation (LNAV)
• No vertical guidance (Non-precision Approach)
– Lateral/Vertical Navigation (LNAV-VNAV) and Barometric/Vertical
Navigation (BARO-VNAV)
• Comparable performance to NPA lateral guidance and vertical guidance using
barometric altimeter
• Requires WAAS or GPS-BARO/VNAV (no DME/DME in USA)
• Best theoretical HAT is 250 ft (rarely attained)
– LPV
• “Near CAT I service”
• Best LPV minima: 250 ft HAT
9
April 2004
© 2004 The MITRE Corporation. All Rights Reserved.
GPS/WAAS/LAAS Approaches (Concluded)
• LAAS (and future WAAS with dual frequency)
– GNSS Landing System (GLS)
• Equivalent of ILS CAT I
• Best GLS/ILS Cat. I minima: 200 ft HAT
LNAV/BARO-VNAV 350’
LPV-1 250’
GLS/ILS 200’
3o
10
April 2004
© 2004 The MITRE Corporation. All Rights Reserved.
Display Sensitivity of GLS/LPV
Approaches
MAWP
Not to scale
Reference: DO 229C (WAAS MOPS)
11
April 2004
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RNAV OCSs
• Although the navigation error is generally constant
throughout the approach for RNAV systems, the
increase in display sensitivity results in progressively
smaller total errors as the aircraft approaches the
runway/NAVAID
• Resultant RNAV OCSs are
– GLS: Identical to ILS
– LPV (APV I):
• Horizontal is identical to ILS
• Vertical is more conservative (closer to ground) to account for
reduced vertical integrity
12
April 2004
© 2004 The MITRE Corporation. All Rights Reserved.
RNP RNAV
• RNP RNAV has potential benefits in the oceanic, en
route, terminal, and approach domain
– RNP-10 implemented in oceanic airspace
• Reduced route separation
– RNP approaches developed at some airports in Alaska
• Significant airport access benefits attained
• Focus of this discussion will be the final approach
segment
13
April 2004
© 2004 The MITRE Corporation. All Rights Reserved.
RNP RNAV Approaches
• RNP RNAV assumes constant display sensitivity and
constant navigational errors
– Nearly constant total flight errors approaching the runway
• Currently use BARO-VNAV vertical profile
– Other profiles are under investigation
• RNP-.3 can be flown with GPS, WAAS, or LAAS
avionics
– RNP-.3 using DME/DME currently not authorized in USA
• RNP RNAV below .3 will require Special Aircraft and
Aircrew Authorization Required (SAAAR)
– Additional certification, equipment, and training
14
April 2004
© 2004 The MITRE Corporation. All Rights Reserved.
2 x RNP Primary Area each side of centerline
1 x RNP Secondary Area
1 x RNP Secondary Area
1 x RNP 1 x RNP
2 x RNP 2 x RNP
Required Navigation Performance (RNP
RNAV)
Not to Scale
© 2004 The MITRE Corporation. All Rights Reserved.
The GPS Approach Minima
Estimator (GAME) Model
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April 2004
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GAME Objectives
• Computer model developed to provide objective estimates
of benefits of IAPs
• Digital airport, terrain and obstacle data
• Simplified approach design criteria
– Straight-in approach with five mile final
• No intermediate segment
• Variable glide-slope possible, but only 3 degrees slope presented
– Missed approach only for GLS/ILS
• Simplified missed approach
17
April 2004
© 2004 The MITRE Corporation. All Rights Reserved.
GPS Approach Minima Estimator
(GAME) Model
Minima Estimation
Software
Repeat for Thousands
of Runway Ends
Approach
Design Criteria
Generate Statistics
0
500
1000
1500
2000
2500
-0.5 -0.25 0 0.25 0.5 0.75 1 1.25 1.5 1.75
LNAV/VNAV Visibility - LNAV Visibility (sm)
Terrain
Data Base
Obstacle
Data Base
Airports
Data Base
18
April 2004
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GAME Airports:
1534 airports and 5073 runway ends
CONUS: 1429
Alaska: 104
Hawaii: 1
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April 2004
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Instrument Approach HATs
0
500
1000
1500
2000
2500
3000
200 (.75)
250-257(.75)
258-327 (1.0)
328-395 (1.25)
396-465 (1.5)
466-534 (1.75)
535-603 (2.0)
604-740 (2.25)
More
Obs tacle s Prevent
HAT (ft) (No-light Visibility (sm))
Number of Runways
GLS/ILS
LPV
LNAV/VNAV
RNP .3
RNP .1
20
April 2004
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Observations
• ILS, GLS, and LPV dominate the lowest visibility minima
• Even RNP RNAV with SAAAR has increased approach
minima at most runways relative to ILS/GLS/LPV
– Some runways will exhibit improved minima
• E.g., Runways in Alaska noted previously
– Despite additional certification, equipment and training
requirements
• Why do the RNP RNAV approaches show reduced
benefits?
– Investigate effect of removing secondary areas from OCSs
– Investigate effect of curved approaches (short finals)
• 3 nm length of final
21
April 2004
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RNP-.3 and LNAV/VNAV-BARO/VNAV
With Secondary Areas
+ .6 nmi wide
.3 nmi wide
LNAV/VNAV Primary and
Secondary Areas
RNP-.3 Primary and
Secondary Areas
22
April 2004
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RNP-.3 and LNAV/VNAV-BARO/VNAV
No Secondary Areas
+ .6 nmi wide
LNAV/VNAV Primary and
Secondary Areas
RNP-.3 Primary Area
23
April 2004
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Effect of Secondary Areas
0
500
1000
1500
2000
2500
200 (.75)
250-257(.75)
258-327 (1.0)
328-395 (1.25)
396-465 (1.5)
466-534 (1.75)
535-603 (2.0)
604-740 (2.25)
More
Obstacles Prevent
HAT (ft) (No-light Visibility (sm))
Number of Runways
RNP .3
RNP .3 No Secondary
RNP .1
RNP .1 No Secondary
24
April 2004
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Effect of Short Finals (Curved Approaches)
0
500
1000
1500
2000
2500
200 (.75)
250-257(.75)
258-327 (1.0)
328-395 (1.25)
396-465 (1.5)
466-534 (1.75)
535-603 (2.0)
604-740 (2.25)
More
Obstacles Prevent
HAT (ft) (No-light Visibility (sm))
Number of Runways
RNP-.3 Short Final
RNP-.3 Normal Final
RNP-.1 Short Final
RNP-.1 Normal Final
25
April 2004
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Observations
• Removal of secondary areas and use of short finals has
some effect at some runways, but RNP RNAV
performance is still not comparable to ILS, GLS or
LPV
• Why?
26
April 2004
© 2004 The MITRE Corporation. All Rights Reserved.
ILS/GLS/LPV -----
RNP-.1 -----
-5000
-3000
-1000
1000
3000
5000
0 6000 12000 18000
Distance from RWT (ft)
Distance from C/L (ft) Distribution of Controlling Obstacles
5000+ LNAV/VNAV Approaches
27
April 2004
© 2004 The MITRE Corporation. All Rights Reserved.
Narrow RNP RNAV OCSs
• Suppose we narrow the RNP RNAV OCS significantly
• Example:
– ILS/GLS/LPV OCS is + 400 ft wide near the runway threshold
– Let 2 x RNP = 400 ft 􀃎 RNP = 200 ft/6076 ft/nm = .033 nm
• No secondary areas
2 x RNP
Not to Scale
28
April 2004
© 2004 The MITRE Corporation. All Rights Reserved.
Effect of RNP-.033
0
500
1000
1500
2000
2500
3000
200 (.75)
250-257(.75)
258-327 (1.0)
328-395 (1.25)
396-465 (1.5)
466-534 (1.75)
535-603 (2.0)
604-740 (2.25)
More
Obstacles Prevent
HAT (ft) (No-light Visibility (sm))
Number of Runways
GLS/ILS
LPV
LNAV/VNAV
RNP .033 No Secondary
29
April 2004
© 2004 The MITRE Corporation. All Rights Reserved.
Observations
• Even with significantly reduced RNP values, the RNP
minima are still not comparable to ILS. GLS, or LPV
• “Culprit” must be the vertical OCS
• As an example, suppose we use the GLS vertical OCS
200'
Touchdown Elevation
34:1 ILS/GLS
27:1 LPV
23:1 RNP/BARO-LNAV/VNAV
954' 2,379' 1,237' 7,983'
3 Glideslope o
185' HAT
250' HAT
668' HAT
954' 1,154' 3,533' 4,770' 12,753'
Not to Scale
30
April 2004
© 2004 The MITRE Corporation. All Rights Reserved.
Effect of GLS Vertical OCS on RNP RNAV
Note: Normally RNP is restricted to 250 ft HAT
minimum. For GLS vertical, a minimum of 200 ft HAT is assumed.
0
500
1000
1500
2000
2500
3000
3500
200 (.75)
250-257(.75)
258-327 (1.0)
328-395 (1.25)
396-465 (1.5)
466-534 (1.75)
535-603 (2.0)
604-740 (2.25)
More
Obstacle s Prevent
HAT (ft) (No-light Visibility (sm))
Number of Runways
GLS/ILS
LPV
LNAV/VNAV
RNP-.033 No Secondary
RNP-.1 No Secondary
RNP-.3 With Secondary
31
April 2004
© 2004 The MITRE Corporation. All Rights Reserved.
Observations
• The use of the improved vertical OCS produced lower
minima for RNP RNAV approaches
– ILS/GLS OCS only proposed as an example
• Complexity of certification for small RNP values (such
as RNP-.033) is unknown
– RNP-.1 will still require SAAAR
• Increased certification, equipment, and training costs
• RNP RNAV and SAAAR will certainly be beneficial at
some airports, but it is clear that there will be no
substantial benefit over ILS, GLS or even LPV at most
airports
• Is there a less costly/easier way to attain good minima
at most airports?
32
April 2004
© 2004 The MITRE Corporation. All Rights Reserved.
Hybrid Approaches
• It may be possible to combine RNP, GLS, and/or LPV
into a single hybrid approach, where RNP RNAV
criteria are used far from the runway, and the aircraft
transitions to a GLS or LPV approach near to the
runway
– Possible application using ILS also
• Such approaches should avoid the extra certification,
equipment, and training of SAAAR
• What would the benefits be of such approaches?
33
April 2004
© 2004 The MITRE Corporation. All Rights Reserved.
RNP-.1 and ILS/GLS/LPV Hybrid
Horizontal Depiction
-5000
-3000
-1000
1000
3000
5000
6000 12000 18000
Distance from RWT (ft)
Distance from C/L (ft)
34
April 2004
© 2004 The MITRE Corporation. All Rights Reserved.
Hybrid RNP/GLS and RNP/LPV
Approaches
0
500
1000
1500
2000
2500
3000
200 (.75)
250-257(.75)
258-327 (1.0)
328-395 (1.25)
396-465 (1.5)
466-534 (1.75)
535-603 (2.0)
604-740 (2.25)
More
Obstacles Prevent
HAT (ft) (No-light Visibility (sm))
Number of Runways
RNP-.3 w/Secondary
GLS/ILS
RNP-.3/GLS/ILS Hybrid
LPV
RNP-.3/LPV Hybrid
35
April 2004
© 2004 The MITRE Corporation. All Rights Reserved.
Observations
• Application of current RNP RNAV approach criteria will
result in higher minima at most airports in comparison to
ILS, LAAS or WAAS-based approaches
– Some airports will benefit, but most will have higher minima
• Improvement of the vertical profile of RNP RNAV offers
significant benefit with respect to approach minima
– GLS vertical OCS investigated in this paper
• Hybrid RNP RNAV and LAAS/WAAS approaches
appear to have excellent capability to achieve the benefits
of RNP and low approach minima while avoiding the
costs of SAAAR
– RNP to GLS and LPV investigated in this paper
© 2004 The MITRE Corporation. All Rights Reserved.
Backup Slides
37
April 2004
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Instrument Approaches to
Juneau, Alaska, USA
38
April 2004
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-1000
-800
-600
-400
-200
0
200
400
600
800
1000
0 100 200 300 400 500 600 700 800 900 1000
Difference (feet)
Number of Approaches
HAT ft)
---GAME HAT (no Missed Approach) – Actual ILS HAT
---GAME HAT (with Missed Approach) – Actual ILS HAT
Effect of the Missed Approach
GAME Validation
39
April 2004
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GLS/LPV Missed Approach Splay
FAA Order 8260.50
40
April 2004
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GLS/LPV Missed Approach Splay
FAA Order 8260.44A
41
April 2004
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RNP Missed Approach Splay
FAA Order 8260.51