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September 2007 stands out in business aviation as the month the FAA commissionedWide Area Augmentation System (WAAS) GPS systems for use in the United Statesfor IFR approaches. This long-awaited upgrade to GPS satellite navigation is acritical step in the FAA’s NextGen plans. According to current FAA plans, no new ILSor VOR/NDBs will be developed. WAAS GPS approval opens up nearly all of theU.S. public use airports for precision approaches. The FAA Flight Inspection Group isprocessing approximately 300 runway thresholds each year. Currently, there aremore than 1,800 approaches at non-ILS airports in 2009, with more to come.

So why is WAAS important to business aviation operations?• WAAS enhances en-route navigation performance over GPS only.• WAAS enhances non-precision approach capability over GPS only.• WAAS allows operators to fly over 1,800 published LNAV/VNAV

procedures as low as 300 feet.• WAAS allows operators to fly the new LPV procedures as low as 200 feet.• WAAS can use GPS for an alternate (LNAV minima).• WAAS offers better missed approaches.• WAAS eliminates the RAIM check.

Approving the WAAS GPS system is only one piece of the process that is required tomake the system of use to you, the business aviation operator. Each of thesubsequent topics will be covered in this booklet, including:• The WAAS equipment selection and installation.• The approval process for the WAAS equipment in the aircraft (STC required).• The operational approval process.• Overview of the airport approval process.

Much has been written on the WAAS GPS topic and is available online. We believeour efforts in finding and condensing this information should address many of yourconcerns on installing and using WAAS GPS in your aircraft.

Duncan Aviation acknowledges the FAA WAAS Groups, the FAA Engineering andSafety Groups, Raytheon Corporation as the provider of the ground infrastructureand the Avionics Manufacturers who are working on the products to make your flyingsafer, easier and affordable.

WAAS equipment is available now for your aircraft. Check out the latest list of LPVapproaches and you will find that you now have access to new and betterapproaches at more airports.

An updated version of this Straight Talk booklet will be available online atwww.duncanaviation.aero/straighttalk. Please use this information for your planning.Feel free to call us with any questions or comments.

Duncan Aviation Avionics Sales Team800.228.4277 • www.DuncanAviation.aero • 800.525.2376

Editor’s Notes

Straight Talk About WAAS

Notes

______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

800.228.4277 • www.DuncanAviation.aero • 800.525.2376

What is WAAS?

WAAS GPS Capable Units

WAAS Operational FactsLPV & ILS Approached by State 18North American WAAS LPV/LNAV/VNAV Coverage 20

Key Terms

WAAS Operational FAQs

4

10

12

24

40

If this book does not contain a worksheet insert page, download one at:www.DuncanAviation.aero/straighttalk or e-mail us at:[email protected].

What is WAAS?

Once you have filled this out, please call Duncan Aviation’savionics installations sales department at 800.228.4277 in LNKor 800.525.2376 in BTL to discuss your WAAS/LPV options.

1. Company_____________________________________2. Location______________________________________3. Contact Information

Name________________ Phone__________________Cell__________________E-mail_______________________________________

4. Aircraft Make______________Model_______________Serial Number__________________Registration #__________________

5. Type of FMS installed___________________________6. Number of FMS installed (circle one) 1 2 37. Type of Autopilot installed________________________8. EFIS Make_____________ Model______________9. Mechanical Flight Director Make__________________

Model________________________________________10. General Avionics Equipment Make_________________

Generation____________________________________11. Part 91 Part 13512. Areas of Operation or Special Needs_____________________________________________________________________________________________________________________________________________________________

WAAS Worksheet

800.228.4277 • www.DuncanAviation.aero • 800.525.2376 5

This graphic depicts the WAAS infrastructure, two geostationary satellites,the U.S. ground reference stations and the international reference stations(Canada & Mexico). The GPS satellites at the top of the graphic representthe legacy network augmented by WAAS.

4 Straight Talk About WAAS

What is WAAS?

In 2007, the FAA completed and certified a significant upgrade tothe GPS system. This new system, dubbed Wide AreaAugmentation System (WAAS) uses a network of over 25 precisionground stations to provide corrections to the GPS navigation signal.The network of precisely surveyed ground reference stations isstrategically positioned across the country including Alaska,Hawaii, Puerto Rico, Canada and Mexico to collect GPS satellitedata. Using this collected error information, a message is developedto correct any signal errors. These correction messages are thenbroadcast through communication satellites to the airborne GPSreceiver using the same frequency as GPS.

WAAS is designed to provide the accuracy, availability andintegrity necessary to allow flight crews to rely on GPS for allphases of flight, from en route through GPS precision approach forall qualified airports within the WAAS coverage area. This providesa capability for the development of more standardized precisionapproaches, missed approaches and departure guidance forapproximately 4,100 ends of runways and hundreds ofheliport/helipads in the U.S. airspace.

WAAS will also provide the capability for increased accuracy inposition reporting, allowing for more uniform and high-qualityworldwide air traffic management. WAAS is a critical part of theFAA’s NextGen program.

WAAS GPS Satellites


In time, the FAA refined their plan and Congress funded WAAS.After years of hard work, the FAA announced WAAS as operationalin 2003. WAAS leased space on a couple of existing satellites toprove the concept was valid and to work out the bugs. Those existingsatellites were not ideally located or equipped to make WAASuseable for precision approaches. (However, GPS was being used foroverlay approaches.)

The most important news on WAAS came in September of 2007.FAA and prime contractor, Raytheon, announced the commissioningof two new geostationary satellites for WAAS. These satellites areideally positioned so that operators in North America haveredundancy. In addition, each of these satellites broadcast anadditional signal that GPS receivers will use to improve their overallaccuracy. As the United States Air Force replaces the earlier GPSsatellites with new Block II/III versions that have higher power andadded reliability, better positional accuracy will be implemented.

Perhaps this summary will make it easier:• Every IFR-certified and installed GPS unit allows the pilot to

descend to LNAV (or Straight-in) and circling approaches.• Baro-VNAV-equipped GPS systems can also descend to

LNAV/VNAV minima.• WAAS GPS receivers can descend to LNAV, LNAV/VNAV and

LPV minima.• Now, the real push for GPS LPV Precision Approaches

has begun.

WAAS is here now and available for your aircraft.

First, a few acronyms explained:(An expanded glossary can be found on page 40.)

WAAS – GPS Wide Area Augmentation System.LPV Approach – Localizer Performance with Vertical Guidance

approach offering the lowest minimums of GPS systems (2008).LP Approach – Localizer Performance, no vertical guidance

from GPS.LNAV/VNAV Approach – Designed for GPS/FMS equipment

using altimeter data for vertical (2003).

GPS has been widely used for aircraft navigation since the 1980s.While GPS is dramatically more accurate than theVLF/Omega/Loran systems in use at that time, GPS was originallydesigned as a military system and was not FAA certified for solemeans use. As the cold war was nearing the end, President Reaganreleased the system for civil use and most recently President Bushended the use of Selective Availability (SA).

With the much improved accuracy of GPS without SA and thedemise of VLF/Omega, the FAA published Advisory Circulars thatallowed GPS to be used for primary means navigation, domestic andoceanic. But a greater need for GPS was evident, that of GPSprecision approaches. On its own, GPS accuracy and reliability wasnot adequate to supplement or replace ILS/Localizer approaches.

The FAA proposed two upgrades to the GPS system. The first wasfor WAAS, a ground station, satellite linked correction system withimproved accuracies over wide geographic areas (SBAS). The secondis LAAS, a local ground station broadcasting (GBAS) radio signalsfor a very limited area with better accuracy than WAAS. The FAAunderestimated and Congress under funded both WAAS and LAASprograms so both programs struggled in development.


WAAS Overview

WAAS GPS Capable Units

800.228.4277 • www.DuncanAviation.aero • 800.525.2376 1110 Straight Talk About WAAS

The selection of the WAAS units for installation in Part 25 aircraftdepends on a number of factors:

• Dual systems may be required to meet FAR 25.1309 &AC 25.1309-1A.

• Panel or Pedestal mount systems must meet Class 3, TSO C145a –Airborne Navigation Sensors Using the GPS Augmented by the WideArea Augmentation System.

• Multiple box FMS systems with remote WAAS receiver must meetClass 3, TSO C146a – Stand Alone Airborne Navigation EquipmentUsing the GPS Augmented by the Wide Area Augmentation System.

• The existing avionics, flight director and autopilot.

Selection of WAAS GPS Capable Units

The installation and certification of the WAAS units forLPV approaches must be done in accordance with thefollowing documents:

• The WAAS/FMS Equipment Manufacturers Installation Manual

• AC 43.13-2B [Large Aircraft] Acceptable Methods, Techniques andPractices – Aircraft Alterations.

• AC 20-138A Airworthiness Approval of GPS Navigation Equipmentfor Use as a VFR and IFR Navigation System.

• AC 90-94 “Guidelines for Using GPS Equipment.

• FAA Order 8900.1 Flight Standards Information ManagementSystem (FSIMS) Volume 4. Aircraft Equipment and OperationalAuthorizations, Chapter 1. Air Navigation, Communicationsand Surveillance.

In general, the approval process references above require a TC orSTC for a WAAS GPS installation.

Duncan Aviation has FAA delegated authority as a SupplementalType Certificate (STC) and Major Repair and Alterations (MRA)ODA (Organization Designation Authorization). This designationallows Duncan Aviation to sign an STC for aircraft alterations onbehalf of the FAA with the authority to approve design data, testsand analysis, as well as make a finding of compliance to theregulations. To support its ODA authorization, Duncan Aviationhas a team of experienced avionics, structural, aeronautical andsystems engineers. The approval allows Duncan Aviation tocomplete STCs for interior and airframe modifications and avionicssystem upgrades.

Garmin 530w

Honeywell FMZ 2000

Universal UNS-1Ew

Rockwell Collins FMS

TSOs, the antenna will be replaced. The new antenna will probably have adifferent footprint and require approved structural modifications.

If LPV requires two FMSs, what if I do not have room for asecond system?

At least one of the FMSs manufacturers will have a solution in thiscase. They are offering a remote–mounted WAAS GPS sensor unitthat serves as the second system. This unit can operate without adedicated Control Display Unit (CDU) in the flightdeck.

How is WAAS/LPV annunciated?

Annunciation for WAAS/LPVcan be displayed on newerEFIS displays (Glass BoxLCDs) or using externalannunciation as depictedbelow. If the EFISmanufacturer decides not tooffer a modification upgrade path to provide the proper annunciation onthe displays, an external annunciation will be required.

What is the required sensitivity of my existing display systemswhen using WAAS GPS?

En route, full-scale Course Deviation Indicator (CDI) deflection istypically 5 miles with an accuracy of +/- 2 miles.

Within 30 miles of the arrival and departure airport, GPS CDI sensitivitytypically transitions to one mile.

When flying an approach (and the approach mode is armed), GPS CDIsensitivity transitions from 1 mile to 0.3 miles approximately 2 milesfrom the Final Approach Waypoint (FAWP).


Is WAAS ready for my aircraft?

WAAS is now ready for most aircraft. Duncan Aviation is in the STCdevelopment process for the new Universal UNS-1xW, Honeywell NZ-2000 v6.1, Rockwell Collins and other GPS–based Flight ManagementSystems for most aircraft.

What must be accomplished to install GPS WAAS equipment inmy aircraft?

For GPS WAAS, you must also use equipment certified by TSO-C145aor TSO-C146a and have the installation done by an appropriate STC.

Safe flight using GPS equipment depends on airworthiness:

1) Does it have the appropriate TSO?

2) Was it installed per AC 20-138 or AC 20-130a?

3) Is it documented? Was it done properly per TC/STC?

If I purchase a WAAS GPS system, am I ready to fly the approaches?

WAAS capable avionics do not automatically mean that you can fly theLPV minima line. You must comply with the certification andoperational requirements as well.

WAAS approaches do not require any special ground equipment at thedestination airport—no localizer or glide slope transmitters are necessary.

I already have GPS. Will WAAS require a separate/different antenna?

Yes. The WAAS message is broadcast on the same frequency as the GPSsignal, so WAAS and GPS share one antenna. Because of the new WAAS


FAQs - WAAS Aircraft Equipment

WAAS Operational Facts

• Lowers the FAA flight inspection costs.

• May increase airspace capacity under the FAA’s NextGen program.

The FAA has announced the decommissioning of some existingNavaids including NDBs, Cat1 ILS, VORs and Markers. Watch yourcharts to see these changes.

Benefits of WAAS include the following:

• Flexibility.

• Better Weather Minimums.

• Creates more alternate airport opportunities.

• Gives a corporate/business traveler closer proximity todesired locations.

• Allows the flight crew to fly precision approaches as low as200 feet, typically below 300 feet.

(Duncan Aviation wishes to acknowledge the FAA, Raytheon,Mitre Corp., Stanford University and the avionics manufacturersfor this information.)


The operation of WAAS GPS equipment requires:

• Your FAA Approved Aircraft Flight Manual Supplement.

• Your FAA Approved Aircraft Flight Manual.

• The equipment manufacturer’s operating/instruction manual.

• FAA Aeronautical Information Manual.

• WAAS NOTAMS.

• Appropriate approach charts.

• Appropriate training for the flight crew using WAAS procedures.

• AC 90-94 “Guidelines for Using GPS Equipment.”

Advantages of using WAAS GPS:

• Safety using Lower Minimums, LPV is typically 250 to 300 feet.

• Extremely Accurate GPS meets air navigation performancerequirements for precision approaches, non-precisionapproaches, en route and terminal phases of flight.

• Better missed approaches.

• Opens up over 1,800 WAAS approaches with thousandsmore to come.

• Affords better weather minimums at many of the airports(some are LPV200 as low as 200 feet).

• Removes the GPS RAIM FDE checking requirement.

• Removes the Low Temperature Approach requirement.

• Uses two GEO satellites for redundancy.

• Approved in 48 states, Alaska and Canada. (Mexico isworking on similar approvals.)


WAAS Operational Facts

#LPVApproaches by State #LPV <260 ft #ILSAlaska 16 12 30Alabama 25 11 26Arkansas 20 13 25Arizona 12 4 18California 35 12 76Colorado 8 5 36Connecticut 7 0 7District of Columbia 3 1 10Delaware 4 0 3Florida 80 19 71Georgia 58 21 53Iowa 27 21 22Idaho 9 8 9Illinois 36 12 55Indiana 32 12 33Kansas 32 26 24Kentucky 15 4 21Louisiana 19 4 23Massachusetts 8 1 23Maryland 6 1 16Maine 8 4 13Michigan 19 4 50Minnesota 24 15 39Missouri 42 14 33Mississippi 26 11 24Montana 7 4 11North Carolina 29 9 51North Dakota 15 11 14Nebraska 54 32 18New Hampshire 5 2 19New Jersey 13 4 16New Mexico 10 8 17Nevada 4 1 10New York 28 14 52Ohio 30 10 45Oklahoma 13 5 30Oregon 14 3 18Pennsylvania 36 12 41Rhode Island 3 1 4South Carolina 19 9 22South Dakota 15 9 12Tennesee 9 7 28Texas 82 54 104Utah 4 0 13Virginia 20 6 25Vermont 1 0 3Washington 22 3 31Wisconsin 32 5 27West Virginia 1 0 12Wyoming 12 8 9


WAAS approach locations as ofFebruary 2008. Total of 1,084WAAS LPV approaches. Totalof 12 LPV 200 approaches.There are over 1,500 ILSapproaches available.


WAAS Approach Locations

LPV200 Service Contour(solid yellow line)

LPV Service Contour(solid red line)

LNAV/VNAV Service Contour(dashed black line, includes LPV)

Color Scale is Vertical ProtectionLevel (VPL)

08-December-2007 13:27:10 GMT(WJH FAA Tech. Cntr., NJ USA)


This FAA graphic shows that nearly all North America has GPSLPV accuracy.

North America WAAS Coverage


GPS NPA (LNAV) refers to a Non-Precision Approach (NPA)procedure which uses GPS and/or WAAS for Lateral Navigation(LNAV). On an LNAV approach, the pilot flies the final approachlateral course, but does not receive vertical guidance for a controlleddescent to the runway. Instead, when the aircraft reaches the finalapproach fix, the pilot descends to a minimum descent altitudeusing the barometric altimeter. LNAV approaches are less precise(556m lateral limit) and therefore usually do not allow the pilot todescend to as low an altitude above the runway. Typically, LNAVprocedures achieve a minimum descent altitude (MDA) of 400 feetheight above the runway.

What is an LPV approach and can I fly LPV approaches withWAAS today?

LPV is the new category of approach that uses the WAAS signaland provides vertical guidance. You can fly LPV with WAASavionics installed, approved and certified for LPV approaches.

Can my aircraft be equipped with only GPS for navigationand be legal for flying in IMC?

The FAA has authorized GPS as the primary means of navigationin certain areas (oceanic and remote). The FAA requires that theaircraft have the appropriate equipment necessary for the route offlight. Furthermore, a GPS approach cannot be used for thealternate if it is also used for the destination when using earlierTSO-C129 equipment. WAAS allows the use of GPS for alternatesbased on LNAV, LPV, LP or better performance. Therefore, it maybe legal to fly a GPS-only equipped aircraft in IMC, but thecircumstances are quite rigorous.

What approaches can I fly with GPS WAAS?

This answer is highly dependent upon your specific equipment andinstallation. Please check the Aeronautical Information Manual.


What is the difference between GPS LPV, LP, LNAV/VNAVand LNAV and are there other types of approaches?

Localizer Performance with Vertical guidance (LPV) is the mostdesired approach. It is similar to LNAV/VNAV except it is muchmore precise (40m lateral limit), enables descent as low as 200-250feet above the runway and can only be flown with a WAAS receiver.LPV approaches are operationally equivalent to the legacyinstrument landing systems (ILS), but are more economical becauseno navigation infrastructure has to be installed at the runway.There are over 1,800 LPV approaches in use today and the FAA ispublishing over 300 new LPV approaches per year.

Localizer Performance (LP) is a recent NPA procedure that usesthe WAAS precision of LPV for lateral guidance and barometricaltimeter data for vertical guidance. These approaches are neededat runways where, due to obstacles or other infrastructurelimitations, a vertically guided approach (LPV or LNAV/VNAV)can not be published. LP approaches can only be flown by aircraftequipped with WAAS receivers. The minimum descent altitude forthe LP approach is expected to be approximately 300 feet abovethe runway.

LNAV / VNAV (Lateral Navigation / Vertical Navigation)approaches use lateral guidance (556m lateral limit) from GPSand/or WAAS and vertical guidance provided by either thebarometric altimeter or WAAS. Aircraft that don’t use WAAS forthe vertical guidance portion must have VNAV-capable altimeters,which are typically part of a flight management system (FMS).When the pilot flies an LNAV/VNAV approach, lateral and verticalguidance is provided to fly a controlled descent and a safermaneuver to the runway. The decision altitudes on theseapproaches are usually 350 feet above the runway.



approaches. We expect business aviation to gain a significantnumber of approaches to airports that were not readily availablebefore WAAS.

Can I use an alternate with a GPS approach?

If you have approved WAAS avionics, you may plan to use anyinstrument approach authorized for use with your WAAS avionicsas a required alternate. You must use the LNAV minima line forplanning purposes in case vertical guidance is not available.

WAAS removes the RAIM and FDE prediction scenarios.

Will WAAS provide a performance comparable to ILS?

WAAS LPV approaches are designed to provide performancecomparable to Category 1 ILS. The WAAS minima are shown oneach Approach Chart. The airport survey determines the minimumheight above terrain allowed. Approaches are being added monthly.

In addition, the data below is extracted from FAA contractorRaytheon Corporation’s measured results.


LPV approaches require WAAS Class 3 equipment built to TSO-C145A or TSO-C146A and installed IAW AC 20-138A. Older TSOC129 GPS receivers may be for VFR-only use, or may only besufficient to fly non-precision GPS approaches. LNAV/VNAV andLPV approaches require additional equipment beyond the basicGPS receiver.

Can I use a WAAS GPS to fly RNAV approaches?

An approved WAAS GPS is qualified to fly the following: WAASLPV, LP, LNAV/VNAV.

When I install WAAS equipment, will I get a RNP?

RNP stands for “Required Navigational Performance.” It is a metricof system navigational capability. The FAA is moving toward aperformance-based national airspace system.

In the future, your ability to fly in certain areas may be governedby your ability to achieve precise navigational performance withinspecific tolerances. RNP-0.3 will be used for approaches and itrefers to .3 nautical mile accuracy. This accuracy may be achievedthrough various means (GPS, WAAS, flight management systemusing automatic DME updates), but your aircraft will be certified toa particular RNP.

Where can I find a current list of WAAS approachprocedures?

The following FAA website is updated several times a year:

http://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/techops/navservices/gnss/approaches/index.cfm

The website lists the approaches that have been completed andpublished. When you receive the published approach chart and youhave the proper equipment with the proper certification, you areready to fly the approach. In the FY2009 budget, Congress directedthe FAA to focus on Non-Part 139 airports for the new GPS


WAAS ACCURACY PERFORMANCEGPS GPS WAAS LPV-200 WAAS LPV-200

Standard Actual Standard ActualHorizontal 95% 36 m 2.74 m 16 m 1.08 mVertical 95% 77 m 3.89 m 4 m 1.26 m

Do you have a timeline regarding when and where WAASapproach procedures are supposed to be rolled out?

In FY2006 over 350 LPV procedures were published.

In FY2006, 287 LPVs were published at non-ILS Runways.

As of June 2009, there are over:

1,800 LPVs,

4,155 LNAV,

1,708 LNAV/VNAV procedures published.

If you need the status of a particular approach, the FAA maintainsa website which provides the production plan for future WAASprocedures over a five-year window. It is available online at:http://avnweb.jccbi.gov/schedule/production

If a favorite airport does not haveGPS approach capability, canyou succinctly break down themechanics/steps in implementing aWAASprocedure and explain each step in the process?

The process is too detailed to show in this booklet. A quick overviewof the requirements are:

• Paved runways over 3,200 feet long by 60 feet wide.

• Non-precision runway markings.

• Runway safety zone.

• Parallel taxiway recommended.

• Medium intensity runway lights.


How many WAAS procedures are planned?

The current FAA goal in the WAAS business case calls forapproximately 8,900 WAAS procedures. This number coincides withall of the available public use runways, IFR and VFR in the U.S.National Airspace System (NAS) that are at least 3,200 feet inlength. The FAA assesses the available runways that do not havepublished approaches each year to establish the priority locationsfor the following year production goals. The 2009 Congressionalbudget requires the FAA to certify non-Part 139 airports first.


TABLE 1 REQUIRED PERFORMANCELPV Performance Full LPV Reg.Availability 99%HAL 40 mVAL 50 m95% Accuracy Vertical 2.0 m

Horizontal 1.5 mProbability of HMI 10-7 per approachTime to Alarm 6.2 sec.Coverage 100% of Continental U.S.

TABLE 2 WAAS LPV (full Localizer Performance with Vertical Guidance)WAAS Requirements WAAS Actual

Measured PerformanceLPV CONUS 100% of Continental U.S. 100% of Continental U.S.99% AvailabilityLPV Alaska 75% of Alaska 88% of Alaska95% AvailabilityVertical Accuracy 2.0 m .95 m

95% bound 95% boundHorizontal Accuracy 1.5 m .60 m

95% bound 95% boundTime to Alarm 6.2 sec. 6.2 sec.Probability of HMI 10-7 0

Can WAAS be used outside the U.S.?

Canada has granted approvals for WAAS-equipped aircraft. Mexicois working on WAAS implementation.

The following Satellite Based Augmentation Systems are underdevelopment. Most are believed to be compatible with a commonspecification outlined by ICAO.

EGNOS – European Geostationary Navigation Overlay Service.The European system will be based upon GPS, GLONASS and theGalileo Satellite System that has been approved, partially fundedand has not been launched. EGNOS is expected to be compatiblewith WAAS, but the EU politics will likely delay implementationuntil 2012.

MSAS – Japan’s Multifunctional Transport Satellite Augmentationsystem is a Satellite-based Augmentation System using theirMTSAT satellites. Raytheon is the prime contractor, which statesthe MSAS will be compatible with WAAS. MSAS was declaredoperational in 2007.

GAGAN – India’s GPS /GLONASS and Geo-Stationary AugmentedNavigation program is expected to be in service in 2010.

SNAS – China’s Satellite Navigation Augmentation Systembelieved to be WAAS-compatible.

GRAS – Australia’s Ground Based Augmentation System usesVHF ground based transmitters instead of satellites for theGPS augmentation. The compatibility with WAAS has notbeen determined.


You should begin by contacting the local FAA Airport District Officeand your state Aeronautics Agency. Requirements are given inAdvisory Circular 150/5300-13. The developmental process can takefrom 12 to 18 months.

How does WAAS know that the correction it sends is validfor my particular location?

The WAAS supplies two different sets of corrections:

1) Corrected GPS parameters (position, clock, etc.)

2) Ionospheric parameters.

The reference stations do not move. They measure all the errorsand provide corrections so the aircraft flying in a particular locationdoes not see those errors.

Can I rely on WAAS to notify me if there are problems?

For safety reasons, WAAS has six seconds to do one of two actions:

1. Correct user position outside the guaranteed accuracy protectionlimits to get back within the protection limits. If WAAS is able tocorrect misleading information within six seconds, there is no lapsein system integrity.

2. Shut-off connections and notify the user not to use. If the systemis unable to correct misleading information in the six-secondtimeframe, it becomes Hazardously Misleading Information (HMI)and should not be used for navigation.

What is meant by “WAAS integrity”?

“Integrity” refers to usability of the satellite signal and means thatthe signal has not been corrupted. Integrity is the ability of asystem to provide timely warnings to users when the system shouldnot be used for navigation as a result of errors or failures in thesystem. WAAS improves upon the integrity of the basic GPS signaland detects much smaller errors more quickly.


When will the WAAS developmental work be complete?

WAAS development work will be complete at the end of 2008. After2008, WAAS will revert to system sustainment and technicalrefresh activities while focusing more on procedure developmentand user avionics. The FAA will continue to add over 300 LPVapproaches annually.

What is the typical LPV approach procedure?

The figure on the next pages depicts a typical published LPVapproach procedure. The title denotes the approach as an areanavigation (RNAV) procedure. Notice that each RNAV proceduretypically includes three of the approach types previously described.This is done to ensure that as many aircraft as possible, of differenttypes and with different equipment, can fly the approach and toprovide operational flexibility if WAAS becomes unavailable.

Some aircraft may only be equipped with standard GPS receivers.They can fly to the LNAV decision altitude. Aircraft equipped withGPS and FMS can fly to the LNAV/VNAV decision altitude. WAAS-equipped aircraft certified for LPV can fly to LPV decision altitude.If for some reason the WAAS service becomes unavailable, all GPSor WAAS-equipped aircraft revert to the LNAV decision altitudeand land safely using GPS-only.


What does the acronym APV mean?

APV is the International Civil Aviation Organization (ICAO) termfor an Approach with Vertical guidance and it refers to specificICAO criteria adopted in May 2000. This approach classificationallows the use of stabilized descent using vertical guidance withoutthe accuracy required for traditional precision approach procedures.

The U. S. has developed criteria for lateral/vertical navigation(LNAV/VNAV) and LPV approach procedures that meet thisapproach classification. The LNAV/VNAV and LPV approachesprovide guidance in both the lateral and vertical planes.

Is there a backup system planned for GPS?

LORAN will continue to be modernized, according to the recentlyreleased U.S. Fiscal Year 2009 budget. System responsibility hasbeen placed within the Department of Homeland Security, whichhas chosen LORAN as the backup for national infrastructureelements that currently depend on GPS. Today, high-accuracy GPStiming is essential to such critical elements as communications,utilities, banking and transportation and a severe GPS outagetoday could be crippling nationwide.

The low-powered GPS signals can be jammed by hackers oradversaries, whereas the updated eLORAN (for enhanced LORAN)offers near-GPS timing accuracy, high-powered jam-resistantsignals and totally different failure modes. eLORAN receivers couldtrack every ground-based LORAN station within reception range,which could provide 25 or more position and timing sources. Stand-alone eLORAN aviation units appear unlikely–manufacturerscurrently envision small eLORAN chips buried as backups insidefuture GPS units. In addition, the U.S. military is replacing theoriginal GPS satellites with higher powered more secure satellites.This will also add to the reliability of GPS signals.



Charting LPV

WAAS Channel Number: CH 97307WAAS Channel Number is a referencenumber assigned to each approach chart.Some of the WAAS FMSs will provide ashortcut to the chart.

WAAS Approach ID: W13AW: WAAS13: Runway 13A: 1st WAAS Approach to RWY 13

Temperature RestrictionDoes Not Apply if using WAAS Equipment

LPV Minimum Line273 ft.

Safe flight using GPS equipment depends on airworthiness:

1) Does it have the appropriate TSO?2) Was it installed per AC 20-138 or AC 20-130a?3) Is it documented? Was it done properly per TC/STC?

Is WAAS/LPV available via Field Approval Process?

Universal Avionics Systems in conjunction with the FAA haveestablished an “Engineering Assisted Field Approval” process bywhich aircraft, which currently have installed Universal FMSs thatare 3D coupled for pseudo ILS approaches, can be upgraded to thenew Universal Avionics WAAS Flight Management Systems withLPV approach capability. Even though this process is considered a“Field Approval” to be used on a specific aircraft and a specificserial number, the process is more complex. One of therequirements called out in this process is to coordinate with anappropriately authorized FAA-designated DER who can support theFAA Form 337. It will also be necessary to work with a Flight TestDER or Flight Test Analyst DER who can evaluate the WAAS FMSLPV approach performance and individual compatibility with theproposed flight guidance displays.


FAQs - WAAS Regulatory & Certification

What are the applicable TSOs & Advisory Circulars?TSO-C145a is “Airborne Navigation Sensors Using the GPSAugmented by the Wide Area Augmentation System.”

TSO-C146a is “Stand-Alone AirborneNavigation EquipmentUsingtheGPSAugmented by theWide Area Augmentation System.”

AC 20-130a is “Airworthiness Approval of Navigation orFlight Management Systems Integrating MultipleNavigation Sensors.”

AC 20-138a is “Airworthiness Approval of GPS NavigationEquipment for Use as a VFR and IFR Navigation.”

AC 90-94 is “Guidelines for Using GPS Equipment.”

What are the differences in capabilities between theWAAS TSOs, STCs, etc.?For WAAS, you must also use equipment certified by TSO-C145a or TSO-C146a. Most general aviation WAAS receiverswill comply with TSO-C146a, which applies to panel orpedestal mounted navigation equipment (as opposed tosensors that provide data to a flight management system).

TSO is a Technical Standard Order and it describes theminimum performance standard for a system or component.

Supplemental Type Certificate (STC) is a document issuedby the FAA approving an installation or modification. TheSTC defines the product design change, states how themodification affects the existing type design and lists serialnumbers of the component affected by the change.


Key Terms

aviator greater position awareness than that derived from using theground NAVAID. Second, although they didn't provide lowerminima, GPS overlays also introduced and validated GPSapproaches to aviation. This initial validation was critical for futureGPS improvements.

HMI – Hazardously Misleading Information.

H/VPL – Horizontal/Vertical Protection Levels. There is one chancein 100 million of the GPS being in error by more than the H/VPL.You will be locked out of LPV if the required levels are not met.Other approaches will be offered if their H/VPL are met.

LAAS – Local Area Augmentation System, under development formore accurate GPS approaches. No completion date has beenannounced, pending funding by U.S. Congress. Refer to GBAS formore detail.

LNAV/VNAV – (Lateral Navigation/Vertical Navigation)approaches use lateral guidance (556m lateral limit) from GPSand/or WAAS and vertical guidance provided by either thebarometric altimeter or WAAS. Aircraft that don’t use WAAS forthe vertical guidance portion must have VNAV-capable altimeters,which are typically part of a flight management system (FMS).When the pilot flies an LNAV/VNAV approach, lateral and verticalguidance is provided to fly a controlled descent and a safermaneuver to the runway. The decision altitudes on theseapproaches are usually 350 feet above the runway.

LP Approach – A GPS approach with Localizer Performance withpilot guided vertical descent (2008).

From AIM 1-1-20: A new non-precision WAAS approach, calledLocalizer Performance (LP) is being added in locations where theterrain or obstructions do not allow publication of vertically guidedLPV procedures. This new approach takes advantage of the angularlateral guidance and smaller position errors provided by WAAS to


AC 43.13-2B – FAA Advisory Circular pertaining to AcceptableMethods, Techniques and Practices - Aircraft Alterations. This AdvisoryCircular contains guidance material pertaining to aircraft alterations.

AC 20-138A – Airworthiness Approval of GPS Navigation Equipmentfor Use as a VFR and IFR Navigation System. This Advisory Circularcontains guidance for GPS installation certification.

AC 90-94 – Guidelines for Using GPS Equipment. This AdvisoryCircular contains guidance for GPS equipment operation.

Approach with Vertical Guidance (APV) – There are actuallythree approach categories now. Precision, Non-Precision andAPV. “APV” approaches are an ICAO recognized term and havedifferent criteria.

FAR Part 25 – Federal Aviation Regulations – AirworthinessStandards. These are the general regulations that apply forTransport Category Aircraft (generally over 12,500 pounds).

FAR Part 25.1309 – Equipment, Systems and Installations.This section covers the requirements for the addition ofequipment and systems.

GBAS – Ground Based Augmentation System. A local areaaugmentation system (also know as LAAS) where the GPS correctionsignals are sent to the aircraft from ground based transmitters.

GPS NPA – refers to a Non-Precision Approach (NPA) procedurewhich uses GPS and/or WAAS for Lateral Navigation (LNAV).

GPS Overlay Approach – These procedures, available in 1994,authorized use of approved GPS receivers to fly existing non-precision instrument approaches. The only difference was thatcourse guidance could come from the GPS system. These proceduresare identified with “or GPS” in the title. The advantage for theseprocedures was twofold. First, overlay approaches provide the



SAAAR – Special Aircraft and Aircrew Authorization Required.SAAAR Approaches are specially authorized and have stringentrequirements. Refer to AC 90-101 for details.

VLF/Omega – A now defunct navigation product. The Very LowFrequency portion used U.S. Navy high-powered transmitters thatwere designed for submarine communications and navigation. TheOmega system was a synchronized Low Frequency Pulsedtransmitter system.

WAAS – The Wide Area Augmentation System or WAAS is a majorimprovement to GPS. A combination of 25 WAAS ground referencestations (WRS) monitor the GPS constellation signals and sendcorrections through two WAAS Master Stations (WMS) up to twogeosynchronous satellites. These satellites then transmit thecorrections to a WAAS–enabled FMS/GPS receiver.

WAAS Channel Number – A reference number assigned to eachapproach chart. If used by a particular manufacturer, the channelnumber provides a shortcut to the chart.

WAAS Containment – Similar to LNAV/VNAV and ILSapproaches, LPV procedures evaluate the Glideslope QualificationSurface. Because of the smaller integrity limit and angularguidance, the size of the obstacle trapezoid is smaller thanLNAV/VNAV. In 2003, the minimum height above touchdown(HAT) value was established at 250 feet. In March 2006, it wasannounced that the WAAS minimum HAT would be lowered to 200feet if all other airport infrastructure requirements are met.

WAAS Alerting – Another major improvement is WAAS alerting.The WAAS horizontal integrity limit is 40 meters on final asopposed to 556 meters for basic GPS. More importantly, WAASprovides vertical integrity, which basic GPS does not. WAASeliminates the requirements for RAIM predictions, but crews stillmust check WAAS NOTAMs. Additionally, on procedures with aninverse W, crews must plan using non-precision approach

provide a lateral only procedure similar to an ILS Localizer. LPprocedures may provide lower minima than a LNAV procedure dueto the narrower obstacle clearance surface.

LPV Approach – Localizer Performance with Vertical GuidanceApproach offering the lowest minimums of GPS systems. RequiresWAAS GPS receivers.

RNP – Required Navigational Performance. It is a metric of systemnavigational capability. The FAA is moving toward a performance-based national airspace system.

SBAS – Satellite Based Augmentation System such as WAAS,EGNOS, etc.

SA – Selective Availability, military scrambling of GPS or nolonger active.

STC – Supplemental Type Certification. The two objectives ofAircraft certification is to encourage and foster the development ofcivil aviation and to ensure aviation safety. One method used by theFederal Aviation Administration (FAA) to fulfill these objectives isthe aircraft certification system through which aircraft design andmodification must be approved. Title 14 of the Code of FederalRegulations (14 CFR) and the Civil Air Regulations (CAR) definethe minimum required safety standards for FAA certification. Bydemonstrating compliance with these regulations, an aircraftmodifier may obtain the necessary FAA approval for a modification.Types of aircraft certification design approvals are determined bythe magnitude and complexity of the change. Aircraft modificationscan be subdivided into minor and major changes (14 CFR part 21,section 21.93). The type of FAA approval is applicable to a givenmodification. Supplemental Type Certificates (STC) are required formost major changes to existing Type Certificate (TC) productsaffected by a modification or installation when the change is not sointensive as to require a new TC (14 CFR part 21, section 21.19).



requirements since vertical NOTAMs are not provided. Theinverse W symbols will be removed as the vertical signalavailability improves at airports. Avionics equipment guidance isfound in TSO-C145– V/VNAV and LNAV.

Why would one fly LNAV / VNAV or LNAV minima if they couldfly LPV? The reason is that some GPS and RNAV (GPS)approaches have LNAV/VNAV, but not LPV minima. Also, if theWAAS system has an outage, the pilot can still fly the LNAVportion. Think of flying the localizer only approach when the ILSglideslope is out of service. There are approximately 1,800 LPVapproaches already published with a production goal of 300 moreLPV approaches each year.


Documents

Straight Talk WAAS