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Everything You Wanted to Know About GPS and WAAS. Everything You Wanted to Know About GPS and WAAS (Unless you are an engineer!). Agenda. Basics of GPS Recent change to AIM, AC 90-100 RNAV, RNP or not? WAAS How it works What can it do for me? Approaches (LPV, LNAV/VNAV)

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Everything You Wanted to Know About GPS and WAAS

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Everything you wanted to know about gps and waas l.jpg

Everything YouWanted to KnowAbout GPS and WAAS

Everything you wanted to know about gps and waas unless you are an engineer l.jpg

Everything YouWanted to KnowAbout GPS and WAAS(Unless you are an engineer!)

Agenda l.jpg


  • Basics of GPS

    • Recent change to AIM, AC 90-100

    • RNAV, RNP or not?

  • WAAS

    • How it works

    • What can it do for me?

    • Approaches (LPV, LNAV/VNAV)

    • SIDs, STARs, Q-Routes, and T-Routes

  • What’s next?

    • Performance-based National Airspace System

  • Q&A

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The Usual Caveats

  • Valid for navigation in the US National Airspace System

  • Does not invalidate or change ANYTHING required by your POI or in your OpSpec

  • Does not supersede ANYTHING in your POH/AFM

  • Some equipment requires specific operational mitigations

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FAA Mission

  • Provide the safest, most efficient aerospace system in the world

    Navigation Services goal

  • Provide safe, cost effective navigation services to meet operational needs of the aviation customer

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The National Airspace System (NAS)

  • 18,000 airports

  • 750 control facilities

  • 4,000 commercial flights per day

  • 100,000 commercial passengers per day

  • Plus thousands of Part 91 operations every day

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GPS Basics

  • Nominal 24 GPS satellites in low earth orbit

  • Each satellite transmits data message

  • Airborne receiver processes message to determine position/velocity/time

  • Navigation function; either in FMS or in GPS (stand-alone)

  • Linear, not angular

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Receiver Autonomous Integrity Monitoring (RAIM)

  • Calculates your position vs. satellites to determine if sufficient for navigation

  • Considers known satellite outages

  • RAIM check for destination and alternate

  • Required for GPS

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  • GPS outages

    • Usually military

  • Satellite outages

    • Used in RAIM prediction

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With Approved GPS, I can:

  • File RNAV

  • Fly an LNAV approach

  • Fly an RNP/RNAV approach

  • Fly a GPS approach

  • …but I can’t file a GPS alternate

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An RNAV Aircraft Can

  • Substitute RNAV for VOR, ADF or DME that is out of service

  • Use as alternative means of navigation guidance (no requirement to monitor VOR, etc.)

  • Extracted from AIM, Section 1-2-3, “Use of RNAV Equipment on Conventional Procedures and Routes”

    • Define “Conventional”

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“Conventional” Is Not RNAV

  • Older TSOC-129 boxes

    • Lack sufficient database memory

    • May lack ability to provide path guidance (path terminators)

    • Suitable for most operations, but not RNAV/RNP

  • No restrictions on newer units

  • Information on specific units under “Policies and Guidance” at: www.faa.gov/about/office_org/headquarters_offices/avs/offices/afs400/afs410

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Fly-By and Fly-Over Waypoints

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Fly-By or Fly-Over – Yes, It Is Important

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Can I Fly An RNAV Procedure?

Answer is in AC 90-100A and online, updated table


Q/T Routes







GNS 430

GNS 530

GNS/CNX 480*













*Needs T2 letter of acceptance

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Regardless Of The System, Remember That

“Pilots may not substitute for the navigational aid providing lateral guidance for the final approach.” (AIM, pg 1-2-6)

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Typical Conventional Arrival

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RNAV Arrival

  • Not a conventional arrival

    • Computer generated waypoints

    • Mix of fly-over and fly-by

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WAAS System

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How WAAS Works

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WAAS Capabilities

  • Why WAAS?

    • Enhances en-route navigation performance over GPS alone

    • Enhances non-precision approach capability over GPS alone

    • Allows WAAS equipped users to fly more than 2,891 published LNAV/VNAV procedures to minimums as low as 300 feet

    • Allows WAAS equipped users to fly new LPV procedures

    • Can use GPS for an alternate (LNAV only)

  • Better than 99.99% availability of system

    • 200’ minimumWAAS specific approaches (LPV)

    • 846 LPV approaches published, with 300 new expected each year

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With WAAS, I can:

  • Skip the RAIM check!

  • Fly an LNAV/VNAV approach

  • Fly an LPV approach

  • Use GPS/WAAS entirely

  • …and I can file a GPS alternate

    • But using the LNAV minima line

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  • TSO-C146 “Stand-Alone Airborne Nav Using GPS Augmented by WAAS)

  • TSO-C145 “Airborne Nav Sensors Using GPS Augmented by WAAS”

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Instrument Approach Update

  • NDBs being reduced

  • No new funding for ILS

  • Expansion of LPVs

  • LPV minimums of 200’

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Localizer Performance with Vertical Guidance (LPV)

  • Flies like an ILS (but better!)

  • Minimums down to 200’

  • Why isn’t it a precision approach?

  • What about the pilot test standards?

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Charting with LPV Minimum Line

WAAS Channel Number

WAAS Approach ID: W24A


24: Runway 24

A: 1st WAAS Approach

To Rwy 24

Temperature Restriction

Does Not Apply to WAAS


LPV Minimum Line

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LPV Production Schedule

  • Currently, 846 LPV approaches

  • Adding 300 per year

  • On the web: gps.faa.gov

    • Click button: GPS/WAAS

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Standard Instrument Departure

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Here is what’s coming!

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Coming Soon…

  • LP approaches

  • Helo point in space approaches

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Why All the Changes?

  • Ask anyone who regularly flies into O’Hare, JFK, ATL

    • Capacity

    • Safety

    • Oh, and money!

  • Seen any new airports under construction?

  • Heard about the anticipated number of VLJs?

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Nav Aid Cost

  • VOR

    • Install = $250,000

    • 20-year life cycle cost = $1,100,000

  • ILS

    • Install = $1,200,000

    • 20-year life cycle cost = $2,700,000

  • Neither figure considers cost of real estate

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Where is this leading?

  • GPS is biggest change to hit aviation since the jet engine!

  • 2007 – decision for drawdown of VORs

  • My personal guess -reduce by 60% over 10 years

  • NDBs are already being divested

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Efficient, Flexible Routing





















Performance-Based Navigation

  • Complete transition by 2025

  • Consistent with ICAO global vision

  • Operational capability based on GPS and augmentations

  • Enhance safety, capacity, efficiency

  • Reduce costs

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Required Navigational Performance (RNP)

  • Major change in technical approach – not sensor specific

  • Complete “system” will be RNP certified

    • Aircraft, nav system, autopilot to provide containment and alerting

  • RNP 2 miles en route, 1 mile terminal, 0.3 for approach

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Larry’s Forecast

  • Satellite-based navigation

  • More takeoff-direct routing

  • ILS-like accuracy en route throughout the NAS

  • Skeleton framework of VORs as mitigation for possible GPS jamming/obstruction

    • Until we work out a jam-proof system

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In The Future, You Will:

  • Have to intimately understand the workings of your GPS receiver (to fly IFR)

    • Incredibly capable, but it’s a computer!

  • Spend more time as a “systems operator”

  • You will either love it, or hate it, but it’s here to stay!

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Three Major FAA Planning Documents

  • Operational Evolution Plan

    • www.faa.gov/programs/OEP

  • Roadmap for Performance Based Navigation

    • www.faa.gov/ats/rnp

  • Next Generation Air Transport System

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The Next Generation Air Transportation System (NextGen) Plan Defines A System That Can Meet Demands For The 21st Century

Trajectory-Based Operations


Operations and Services

Precision Navigation

Weather Integration


Information Sharing

Surveillance Services

Equivalent Visual Operations

Super Density Operations

Layered, Adaptive Security


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Navigation Evolution Customer Council (NECC)

  • Council made up of government and industry members

  • Created by Director of Navigation Services to:

    • Implement the navigation evolution roadmap

    • Adjudication of roadmap comments

    • Develop roadmap updates

    • Liaison between policy-makers and the aviation community

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  • Contact me at:



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GPS Inflight Problem Solving



Does the Damn Thing Work?


You Idiot!!!

Don't Mess with It?

Should You Mess with It?



Does Anyone Else

Know How to Use It?

Hide It?


You Poor



Will You Catch Hell?



Can You Blame

Someone Else?

Trash It?




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