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WAAS Commissioning: System Procedures and Considerations

This article explores the commissioning process and considerations for the Wide Area Augmentation System (WAAS), including a study conducted by Ohio University and MITRE on WAAS limitations and future challenges. It also discusses the status of GPS procedures and the benefits of WAAS capability for GNSS procedures.

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WAAS Commissioning: System Procedures and Considerations

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  1. COMMISSIONING THE WIDE AREA AUGMENTATION SYSTEM Jimmy R. Snow

  2. OVERVIEW • WAAS System/Procedures • WAAS Commissioning Considerations • Ohio University Study • MITRE Computer Modeling • MITRE/Flight Inspection Validation • WAAS Receiver • WAAS Limitations • Future Challenges

  3. GNSS RNAV PROCEDURES LPV Takes Advantage of WAAS Capability Equivalent to Localizer Lateral With Vertical Between ILS and LNAV/VNAV, HAT 250 ft & Up LNAV/VNAVVertically Guided Approach With Decreasing Vertical Obstruction Clearance, HAT 350 ft and Up LNAVNon-Precision Approach With 250 ft ROC, Smaller Protected Area Than VOR, No Vertical Guidance CIRCLING Approach Procedure to a runway and then Maneuver to Land on Another Runway

  4. Status Of FAA GPS Procedures (9/22/03) Year97 98 99 00 01 0203 GPS Proc Published 573 516 531 504 447 618 510 TOTAL LPV 7 LNAV/VNAV Published 613 LNAV Published 3,237 Military/Specials 237 GPS Proc Published 4,094

  5. WAAS COMMISSIONINGCONSIDERATIONS • WAAS Commissioning Date Established Approximately Two Years in Advance • Scheduled on Procedures Publication Date, July 10, 2003 • Estimated Over 600 LNAV/VNAV Approaches Published for FMS Baro VNAV Operations • Over 3,000 LNAV Approaches Published for TSO C-129 Receivers • Very Limited WAAS Flight Inspection Capability (Prototype MMR Receiver in Lear 60) • Technical Center WAAS Coverage Chart and Outage Records Used to Restrict Certain LNAV/VNAV Approaches • Numerous Discussions With Certification and Flight Standards

  6. WAAS COMMISSIONING OPTIONS • No Flight Inspection or Evaluation of Procedures • Evaluate Each Procedure on Next Periodic (One and Half Years or Longer to Evaluate All) • Surge Effort After WAAS IOC (up to 1,000 Flight Hours) • Non-Traditional Evaluation of Existing Procedures

  7. OHIO UNIVERSITY SUPPORT • Initiated Discussions With Ohio University, Avionics Engineering Center May 2001 • Established Procedure Parameters With FAA Working Group • Held Discussions With Ohio University to Evaluate WAAS Requirements • Established a Technical Task Directive With Ohio University July 2001 to Evaluate WAAS Commissioning Requirements • Study Delivery Not Later Than Nine Months After Task Signed

  8. FLIGHT INSPECTION COMPARISON • GPS/Baro VNAV • Obstacle Evaluation • Standard Instrument Approach Procedure (Section 214) • Procedure Design (Database, Waypoints, Accuracy) • Electromagnetic Spectrum (RFI) • WAAS LNAV/VNAV • Obstacle Evaluation • Standard Instrument Approach Procedure • Procedure Design • Electromagnetic Spectrum • Geosynchronous Satellite Signal

  9. OHIO UNIVERSITY CONCLUSIONS • Result • Inspection of GPS/Baro VNAV Procedures Should Accomplish All Anticipated WAAS LNAV/VNAV Requirements • EXCEPT Ensuring Adequate GEOSAT Signal Coverage • GEOSAT • Provides Integrity Information, and Differential Corrections • Without, WAAS Receiver Reverts to LNAV Only Capability • Thus, LNAV/VNAV Procedures Can Not Be Conducted

  10. OHIO UNIVERSITY STUDY ASSUMPTIONS • Assumptions • The inherent WAAS monitoring is capable of detecting system faults within the required time-to-alarm • The WAAS receiver reverts to a GPS-only capability in the absence of a GEOSAT signal • The FAA has authorized WAAS for supporting LNAV/VNAV approach procedures • The SIAP procedure has been previously commissioned for GPS/Baro VNAV • The availability of GPS/Baro VNAV and WAAS LNAV/VNAV is at least 95 percent • The descent altitude is the same for the WAAS LNAV/VNAV and GPS/Baro VNAV procedures • There is a high-correlation between predicted (monitoring) and actual WAAS system performance

  11. STUDY CONCLUSIONS • ~ 600 GPS/Baro VNAV Procedures Expected to be Commissioned Before WAAS IOC • Inspection of GPS/Baro VNAV Procedures Should Accomplish All Anticipated WAAS LNAV/VNAV Requirements EXCEPT Ensuring Adequate GEOSAT Signal Coverage • Computer-based GEOSAT Coverage Screening Models May be Used to Streamline Flight Inspection Process (To determine if GEOSAT is shadowed on final approach segment)

  12. STUDY RECOMMENDATIONS (1) • The Comparison of GPS/Baro VNAV and WAAS LNAV/VNAV Flight Inspection Requirements Should Be Repeated Once Formal Criteria Are Available in FAA Order 8200 • The Feasibility and Benefit of Developing a Screening Model for Assessing GEOSAT Signal Coverage Should Be Assessed Further • Low Confidence Cases, the WAAS LNAV/VNAV Procedure Should Be Flight Inspected Before Being Authorized for Use,Low Priority

  13. STUDY RECOMMENDATIONS (2) • Marginal Confidence Cases, the WAAS LNAV/VNAV Procedure Should Be Flight Inspected Before Being Authorized for Use, High Priority • High Confidence Cases, WAAS LNAV/VNAV Operations Authorized and Inspection Performed During Next Periodic Inspection of GPS/Baro VNAV Procedure • For WAAS Procedures Authorized Prior to Formal Flight Inspection, Authorization Should Be Withdrawn if a “Problem Report” Is Received

  14. SECOND PHASECOMPUTER MODELING • FAA Contacted MITRE, Center for Advanced Aviation System Development For Assistance (CAASD) • MITRE Advised They Could Modify an Existing Software Program to Do What Ohio University Recommended • Meetings Were Scheduled to Discuss: • Establishing an Agreement Between FAA and MITRE • Delivery Schedules • Evaluation Requirements • Data Requirements

  15. FAA-MITRE AGREEMENT • AVN Would Provide MITRE the Following: • Airport Identifier • Airport Reference Point (latitude/Longitude) • Airport Elevation • Airport Priority for Screening • If Available Airport Name and Location • MITRE Will Evaluate Each Airport Using the Following Criteria: • Evaluate a point 250 ft Above the ARP From 090 to 270 Degrees • At Least One WAAS GEO is More Than 10 Degrees Above the Horizon • No Terrain Within 40 nm of the ARP More Than 5-deg Elevation Angle Viewed From 250 ft Above the ARP • MITRE Would Use Worst-case WAAS GEO Positions • MITRE Would Validate the Computer Model and Peer Review Results

  16. Elevation Angles in USA and Canada(POR and AOR-W)

  17. TERRAIN MASKING:Forty Nautical Miles Geo Mount Ranier (14,400 ft) 10° (minimum) ARP (Sea Level) FAF (Sea Level) 4.5° 10 nm 30 nm

  18. TERRAIN MASKING:Results • An Airport Passing the Screening Test Will Not Have Geo Masking Due to Terrain and Should Not Require Re-flight Check For Terrain • A detailed look at the airport is not required • Failure of the Screening Does Not Necessarily Imply That GEO Masking Will Occur During an Approach to that Airport • Failure implies that a closer look at the airport is warranted • Availability of LNAV/VNAV Approaches Was Not Addressed

  19. VALIDATION EFFORTS • AVN Airport Database Entries Were Compared With Jeppesen and Other Databases • GEO Angles Were Computed by Several Methods With No Significant Differences Between Methods • Terrain Masking Code Was Checked Independently • Terrain Results Were Spot Checked With Sectional Charts • AVN Will Spot Check Some Airports During a Later Validation Check

  20. AIRPORT GROUP ONESummary • 223 Total Airports With RNAV (LNAV/VNAV) Approaches Developed by AVN • 215 Airports Passed Screening • GEO > 10 Degrees Elevation and • Terrain to South < 5 Degrees Elevation • 8 Airports Failed Screening • 3 Failed for Terrain • 5 Failed for GEO Elevation • 3 in Northern Alaska

  21. AIRPORT GROUP TWOSummary • 155 Total Airports With RNAV (LNAV/VNAV) Approaches Planned by AVN • 142 Airports Passed Screening • GEO > 10 Degrees Elevation and • Terrain to South < 5 Degrees Elevation • 13 Airports Failed Screening • 12 Failed for Terrain • 1 Failed for GEO Elevation

  22. AVN VALIDATION • MITRE Evaluated 378 Airports/AVN Flight Inspected 65 Airports To Validate MITRE results • 11 of the 21 Identified by MITRE Did Not Have GEO Coverage • 2 Additional Airports of the 65 Would Not Support VNAV For Geo Coverage • AVN Accepted the Results As Satisfactory

  23. WAAS MMR RECEIVER • Have Six Collins MMR Receivers With WAAS and LAAS • Two Lear 60s Have WAAS Capability • Due to No TSO Receiver and No STC, Aircraft in Experimental Status • Currently in a MOPS “Beta” Configuration • With the FMS We Must Change the MMR Into “Delta” Configuration, Estimate 2 Years • LPV and LAAS Have FAS Datablock That the AFIS Reads • Aircraft Flying LNAV/VNAV While AFIS Evaluates LPV • New Contract Let to Complete VFR STC (estimate completion January 05)

  24. LPV FLIGHT INSPECTION RESULTS

  25. ILS vs WAAS LPV Flight Inspection Comparison ILS Glideslope WAAS Approach

  26. WAAS LIMITATIONS • Inverse W on RNAV Approach Charts/Limitations • Indicates WAAS Outages May Occur Daily (32 airports) • WAAS NOTAMS Are Not Provided For the Procedure • Use LNAV Minima For Flight Planning (Destination or • Alternate) • If Receiver Indicates LNAV/VNAV or LPV Available • Guidance May Be Used • If WAAS Is Lost Revert to LNAV Minima If Receiver • Allows or LNAV Data Is Available • WAAS VNAV NA on RNAV Charts That Did Not Pass MITRE Modeling and Flight Inspection

  27. INMARSAT 3 POR 178°E INMARSAT 3 AOR/W 54°W INMARSAT III COVERAGE

  28. Jimmy Snow NAVIGATION CONSULTANT 405-249-4329 cjsnow@cox.net

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