1. Alternative Positioning, Navigation, and Timing Initiative
Leo Eldredge, Manager GNSS
FAA Navigation Services
Stanford University, California
August 2010

2. Federal Airways – Current

3. Current Alternative Positioning
ADS-B Surveillance
Uses GNSS for primary positioning
Secondary Surveillance Radar (SSR) Backup
Only a subset of existing SSRs will be retained over the longer term
Multi-Lateration Used to Validate GPS Position
Performance Based Navigation (PBN) Backup
Transport Category Aircraft rely on DME/DME/INS + ILS
Optimized DME retained to support enroute and terminal PBN
ILS retained for final approach guidance
General Aviation aircraft rely on VORs, (not DME equipped)
VOR not an optimum solution for PBN
Continuation of Current State Requires Recapitalization of VORs - ~$1.0B Investment

4. Navigation Services Evolution
Point-to-Point
Jet / Victor Routes
SIDs / STARs, ILS
Primary
VOR/DME
NDB, VORTAC
TACAN
Alternate/
Substitute
GPS, WAAS
Current
PBN
TRANSITION
Q / T Routes
Direct TBO Routes
RNAV SIDs / STARs
RNAV(GPS)
RNAV(RNP)
GPS, DDI
WAAS, LAAS
Other GNSS ?
DD w/o I ?
APNT ?
2025
NextGen

5. GNSS Enables PBN and ADS-B
Navigation
(> 99.0% Availability)
Surveillance
(>99.9% Availability)
Positioning
Accuracy
(95%)
Containment
(10-7)
Separation
NACp
NIC
GNSS PNT
(99.0 – %)
En Route
*10 nm
20 nm
5 nm
308m
(7)
1 nm
(5)
GPS
*4 nm
8 nm
*2 nm
4 nm
Terminal
*1 nm
2 nm
3 nm
171m
(8)
0.6 nm
(6)
LNAV
*0.3 nm
RNP (AR)
*0.1 nm
**0.1 nm
2.5 nm
DPA
0.2 nm
SBAS
LPV
16m/4m
40m/50m
LPV-200
40m/35m
GLS Cat-I
40m/10m
2.0 nm
IPA
121 m
GBAS
GLS Cat-III
16m/2m
APNT
3 nm
171m
(8)
0.6 nm
(6)
DME
Only
Gap
LNAV
*0.3 nm
This chart shows the linkage between operational capabilities for navigation and ADS-B separation standards enabled by GNSS positioning, navigation, and timing services. Each capability has an accuracy component and an integrity value the establishes a guaranteed limit of performance.
* Operational requirements are defined for total system accuracy, which is dominated by fight technical error.
Position accuracy for these operations is negligible.
** Containment for RNP AR is specified as a total system requirement; value representative of current approvals.
Dependent Parallel Approach (DPA)
Independent Parallel Approach (IPA)
Surveillance Integrity Level (SIL)
Navigation Integrity Category (NIC)
Navigation Accuracy Category
for Position (NACp)

6. Alternatives Considered (so far!)
Optimized DME Network
Passive Multi-Lateration
Pseudolite
Other?

7. Optimized DME Network 7

8. 1100 DMEs in Current Nework

9. DME-DME Alternative Strengths Weaknesses
Leverage existing technology and systems
Least Impact on Avionics for Air Carriers
Weaknesses
Significant Impact on Avionics for General Aviation
General Aviation avionics are unavailable
DME-DME equipped aircraft without Inertial are not currently authorized to fly RNAV/RNP routes
DME-DME, even with Inertial, is not authorized for operations less than RNAV/RNP-1.0
DME-DME interrogations saturate in very high traffic environments
Will require retention and capitalization of nearly half the VORs unless GA equipped with DME/DME inertial

10. Wide Area Multi-Lateration10

11. Passive Wide-Area Multi-Lateration (WAM)
1 –Aircraft Transmits ADS-B Signal
6 – Aircraft Uses Own Position for Navigation
5 - TIS-B Sends
Position to Aircraft
Combined DME/GBT Network
2 - WAM Receives Signal
3 - Aircraft Position Determined
4 - Aircraft Position Sent to GBT’s 11

12. WAM Operational at Steamboat Springs
This is an example of a wide area MLAT system implemented in Colorado. Typically, a wide area MLAT system consists of 60 or fewer receive stations and one processing facility. The primary purpose of MLAT in this case is to support surveillance operations, not aircraft navigation.

13. Approaches Histogram NavCanada Independent Verification Of Data
 Instrument Procedures
Meters
Feet
Average
9.4
30.8
Max
81.3
266.9
Min
0.0
Median
8.0
26.1
Std. dev
26.3
Outputs
2378
1-sigma
11.0
36.1
2-sigma
23.0
75.5

14. TIS-B with MLAT Control Station FAA Ground Based Transmitter (GBT)
(SSR)
FIS-B
The concept for passive MLAT-based backup navigation extends TIS-B broadcast the MLAT-determined aircraft position information for all participating aircraft. Is it not known if the throughput of the TIS-B broadcast has enough capacity to include all participating aircraft projected for the future in high density airspace.
Concept to use TIS-B to provide ADS-B equipped aircraft with backup positioning for navigation using MLAT

15. 656 GBT’s for National Coverage
The SBS program is considering the implementation of MLAT at all of the planned ADS-B ground-based transmitters (GBT). Approximately 650 GBT’s are needed to provide single-thread national coverage. It is not known what aircraft positioning accuracy could be achieved, if the GBTs are combined into an MLAT network.
Communication Coverage: Not Navigation

16. Combined Network of DMEs and GBTs

17. MLAT Alternative Strengths Weaknesses
Minimal impact on existing avionics for surveillance
Accuracy demonstrated to be within target levels
Compatible with existing WAM systems
Creates additional benefits for users who equip with ADS-B In
Weaknesses
Frequency congestion on 1090ES may limit availability
Integrity monitoring and time to alert necessary to meet navigation requirements may be very challenging
More sites to meet requirements due to limited signal range
Capacity limited in high density traffic environments
Requires a GPS-independent common time reference
Significant investment in processing facilities and terrestrial communications network may be required
Use of MLAT for navigation requires avionics changes

18. Pseudolites 18

19. Pseudolite Alternative Concept
Aircraft Calculates Position
RAIM Based Integrity Solution
Combined Network of DME/GBTs etc
GPS-Independent Time Reference
1 Hz Message ID and Transmit
PNT Data Broadcast Channel

20. Pseudolite Alternative
Strengths
Unlimited capacity
Aircraft based position and integrity solution
Potential to leverage use of existing DMEs and GBTs
Modified to transmit the PL signal
Potential to use a variety of FAA transmitters to increase coverage.
Weaknesses
Minimum of 3 sites required to compute aircraft position
Common GPS-independent timing reference needed
Greatest impact to aircraft avionics
Least mature concept, no avionics in development and no standards
Will require retention and capitalization of nearly half the VORs unless GA equipped with pseudolite avionics

21. The APNT Initiative within the FAA’s Lifecycle Management System
Service Analysis
Concept Requirements Definition
Initial Investment Analysis
Final Investment Analysis
Solution Implementation
In-Service Management
Research and Systems Analysis
You Are Here

22. Questions