1. ILA 32 (Boulder, CO) - Page 1

2. Development of An Integrated GPS/Loran Prototype Navigation System for Business and General Aviation Applications by
James Davis, Ph.D. and Steve Williams
FreeFlight Systems (Waco, TX)
Richard Ferrier and Linn Roth, Ph.D.
Locus, Inc. (Madison, WI)
purchased the total assets of Trimble Navigation’s Commercial, Business and Helicopter division, located in Austin, TX in July of An interesting note: Steve Williams, President of FFS wife is an attorney who incorporated Charlie Trimble back in 1978 when Trimble first started. Since 1990 more than 60,000 civil and military GPS systems have been delivered.
FreeFlight was able to retain the long-term key employees of Trimble and move several of them from Austin to Waco, 100 miles to the north. Although, I have only been with the company for a short time, the folks at FFS ***
ILA 32 (Boulder, CO) - Page 2

3. GPS/WAAS Benefits vs. ILS
GPS/WAAS offers:
Primary means of navigation
More direct routes & lower MEAs
Some precision approach capability (with WAAS Classes 2 & 3)
Decommission of high cost, ground-based navigation equipment
Less onboard avionics
Increased airspace capacity
ILA 32 (Boulder, CO) - Page 3

4. Additional Benefits Efficiency Precision approach
Back-up for all current ILS approaches (250/¾)
Usable with advanced procedures
LNAV/VNAV
350’
WAAS RNP can provide lower minima at airport
WAAS will provide a backup precision approach capability at all runways currently being served by ILS. This capability will provide the same visibility requirements as Cat I ILS and will only result in a 50 foot higher decision height.
As is the case earlier with Washington National, WAAS is not constrained to flying straight in approaches and can provide an advanced procedure capability to runways currently not able to be serviced by conventional navigation aids.
LPV 250’
ILS 200’ 3o
ILA 32 (Boulder, CO) - Page 4

5. GPS Vulnerability Concern with GPS as sole means of navigation
“Like any radionavigation system, GPS is vulnerable to interference that can be reduced but not eliminated.” [Volpe Report (2001)]
Susceptible to unintentional disruption
Ionospheric effects, blockage from buildings, interference from narrow & wideband sources, etc.
Susceptible to intentional disruption
Jamming & spoofing of GPS signals
Disruption of GPS ground stations & satellites
ILA 32 (Boulder, CO) - Page 5

6. Mitigating GPS Vulnerability
“Utilization of backup systems and procedures to GPS in applications where the consequences of losing GPS are unacceptable will ensure optimum safety.” [Volpe Report (2001)]
Recommendations in Volpe Report:
Encourage development of aviation certifiable Loran-C receivers in the event Loran-C becomes a viable backup
Continue the FAA’s and USCG’s Loran-C modernization program until it is determined whether Loran-C has a role as a GPS backup system.
(Note: Much Loran infrastructure already in place)
ILA 32 (Boulder, CO) - Page 6

7. FAA Response
Team of academic, government, and industry personnel assembled to assess Loran
FAA Program Manager: Mitchell Narins
Determine if Loran can meet non-precision approach RNP 0.3 as well as stringent requirements for availability, integrity, and continuity
Fabrication of integrated GPS/Loran prototype navigation systems for FAA flight tests
Rockwell Collins and Locus, Inc.
FreeFlight Systems and Locus, Inc.
ILA 32 (Boulder, CO) - Page 7

8. Why Locus, Inc.?
Designs, supplies, and supports radionavigation products
SatMate is a digital, all-in-view Loran receiver
Adaptive filtering
Digital noise blanking
Realtime ASF corrections
Proprietary DSP techniques
Locus provides both E-field and H-field antennas
Combination GPS/H-field antenna for this program
ILA 32 (Boulder, CO) - Page 8

9. Why FreeFlight Systems?
Avionics products aimed primarily at aircraft other than air transport class (vs. Rockwell Collins)
FFS created in 2001 with the acquisition of the Business and Commuter Aircraft segment of Trimble Navigation
Choice supports goal of a GPS/Loran product aimed at GA aircraft, business aircraft, regional aircraft, etc.
Product range includes FAA-certified GPS/WAAS
WAAS Class 1: Non-precision approach (LNAV)
WAAS Class 2: LNAV/VNAV (VPL = 50 m)
WAAS Class 3: GLS (VPL = 12 m)
ILA 32 (Boulder, CO) - Page 9

10. FreeFlight Systems & Locus Effort
Development of a two-unit, prototype integrated GPS/Loran system using 3 principal components:
FreeFlight Model 2101 Approach Plus GPS/WAAS Navigation System
Locus Beta-2 prototype SatMate 1030 Loran Receiver System
AeroAntenna GPS patch antenna and a SatMate H-Field Loran antenna contained in an Bendix-King ADF radome for flight test
Also, software, integration, and test effort.
ILA 32 (Boulder, CO) - Page 10

11. Model 2101/SatMate Prototype
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12. GPS/Loran Features SatMate modified to incorporate:
Real-time ASF corrections for improved accuracy, availability, and continuity
Automated GRI and navigation station selection
Digital front-end to enable adaptation to changes in RF environment
Model 2101 modified to:
Provide front-panel GPS/SatMate control
Accommodate SatMate output at 115 KBaud
Provide WAAS-Class 1 accuracy
Vert/Horiz CDI added for realtime, simultaneous monitoring & comparison of GPS and Loran cross-track course deviations
H-field and GPS antennas in radome housing
H- vs E-field: P-static immunity, higher SNR, lower ECD, no GND
ILA 32 (Boulder, CO) - Page 12

13. Scatter Plot for Antenna Rotation
Loran scatter plot for antenna rotated 360o (vertical centerline)
Data relevant to aircraft turns
Black - Early antenna
Excursion~165 ft (max 240 ft)
Green-New GPS/H-field antenna
Loran preamp update, better H-field antenna tuning, and better QA of ferrite rod & cables
Excursion ~ 65 ft
If Loran chains better controlled, excursion < 12 ft
ILA 32 (Boulder, CO) - Page 13

14. Two-pass CW Auto Driving Test
Using GPS/H-field antenna
Yellow trace: GPS baseline
Black trace offset towards bottom of the plot:
Loran data w/o ASF corrections
Black trace more closely aligned with the GPS track:
Loran data corrected on-the-fly with ASF corrections stored on a flashcard inside the SatMate
ASF values previously gathered at Locus facility in Madison
ILA 32 (Boulder, CO) - Page 14

15. Future Effort (Phase II)
Proposal submitted to FAA on 22 August 2003
GPS/WAAS and Loran combined in a single Dzus-mount enclosure (cf. Model 2101, but 1-7/8” higher)
Capability to simulate loss of WAAS coverage, loss of GPS integrity, and total loss of GPS enables assessment of Loran as a back-up to GPS
Multiple navigation solutions with goal of RNP 0.3 accuracy & integrity
GPS only
Loran only
Integration of GPS and Loran position & integrity data
ILA 32 (Boulder, CO) - Page 15

16. Acknowledgement Contract DTFA01-98-C-00061 Sponsorship
Task Order #048 (currently at MOD 011)
“Development of Prototype H-Field Electronics and Software for Initial FAA Flight Tests”
Sponsorship
FAA Navigation & Landing IPT, AND-700
FAA Navigation & Landing Team, AND-740
ILA 32 (Boulder, CO) - Page 16

17. References
Enge and van Graas, “Chapter 6 - Integration of GPS and Loran-C”, Global Positioning System: Theory and Applications Vol. II (ed. by Parkinson, et.al.), AIAA (1996) pp
Roth, Doty, & Hwang, “GPS Safety Net”, GPS World, 14:5 (May 2003) pp
Roth et.al., “Performance of DSP-Loran/H-Field Antenna System And Implications For Complementing GPS”, Navigation, 49:2 (Summer 2002) pp
ILA 32 (Boulder, CO) - Page 17

18. FAA References
John A. Volpe National Transportation Systems Center, “Final Report - Vulnerability Assessment Of The Transportation Infrastructure Relying On The Global Positioning System” (August 29, 2001) 113 pages. (
FAA, “Executive Summary IRB on FAA’s WAAS” (January 18, 2001) 3 pages.
ILA 32 (Boulder, CO) - Page 18