In this issue:

GPS Aids WTC Recovery

Effort....................1

Coastal Waypoints to Enhance

VFR Flight........2

Industry Spotlight: WAAS

and Agricultural Aviation....3

Satellite Navigation-Helping

to Meet Environmental

Requirements.....................4

The WAAS and PRN 22......5

LAAS Testing at the University of Oklahoma...................6

RNAV Route Development...................7

General Comments on the

Characteristics of Test and

Evaluation of Augmented

GPS for NAS.........................7

Global Positioning System

Approach Minima Estimator

(GAME)..........................9

Navigation Workshop.........9

Code-Carrier Coherence

(CCC) Monitor..................10

New Special Copter RNAV

Approaches and Departure

Procedures Under Development in California................12

Results of Early LORAN-C

Modernization Testing.......12

The Lighter Side...........14

GPS Aids World Trade Center

Recovery Effort

By Shelby Wheeler,

GPS TAC

Its hard to imagine a

crime scene the size of

the World Trade Center.

By now, most of us have

heard the statistics; millions of tons of rubble encompassing a vast 16-

acre site. Indeed, the recovery effort at ground

zero is no small task.

In fact, within a week of

the WTC disaster, the Fire Department of New York (FDNY) was waiving the white

flag. The recovery method being used was just not working. Firefighters were tagging

items and jotting down descriptions and information regarding the date, time, and

estimated location by hand, often guessing on an items exact location. This was

not an easy task on such an immense site, containing few landmarks and changing

every day. The items were assigned a tracking number, and transported to the landfill, warehouse, or medical examiners office. The information was then manually

entered into a database, in order to track the items found. This process was laborious

and inefficient, and often resulted in mismatched tracking numbers and inaccurate

location data.

Considering the importance of the exact location of evidence to fire officials, engineers, and the ongoing criminal investigation, the battalion chief in charge of the

recovery effort, Joseph W. Pfiefer, started looking for a better way. On September 19,

the ground-zero team met with numerous technology companies to discuss possible

technological solutions.

The solutions selected by the FDNY, along with other Federal and state agencies,

were hand-held computers and bar codes, from Symbol Technologies, and global positioning satellite applications and real-time tracking database, from Links Point, Inc. Photo provided by Links Point, Inc.
2

Within three days, Links Point created database software

to run on the Symbol PPT 2800, a modified handheld rugged enough to withstand heat, dust, and long hours. Using the PPT 2800 with a GPS attachment, firefighters select a description of the item found and can automatically

capture the time, date, and location of the item with an

accuracy of three to nine feet. Additionally, the firefighters

are able to tag the items with a barcode and scan that

barcode with the device in order to match the item with

the electronic record. The data is then uploaded directly

from the handheld and connected with a database, which

uses Geographic Information System (GIS) technology

with mapping software.

In the past, GPS has not worked very well in Manhattan,

due to the canyon effect of the citys skyscrapers. However, the large space created by the WTCs collapse has

opened up the skyline enough for sufficient signal reception. The exceptions to this are some of the outlying edges

of the site, where GPS coverage stops. To remedy this

situation, officials are examining the idea of erecting an

antenna across the highway from the site, on 3 World Financial Center, which would improve reception of the satellites signals in those areas.

In addition to the tireless New York firefighters and rescue workers, GPS, along with other cutting-edge technologies, is lending a helping hand in the effort to get

back to normal. With the new technology in place, data

capture rates have increased and data errors have decreased. The FDNY now has accurate location information on all items recovered from the site, and the human

error associated with the manual tagging of items and input of data has been eliminated. It seems technology has

come to the rescue.

Coastal Waypoints to

Enhance VFR Flight

By Jack Schroeter, GPS TAC / Southern Region (ASO-520)

Beginning this winter, VFR pilots transiting the coastal

areas of the southeastern United States will have a new

tool for navigation. Sixty-eight VFR waypoints have been

developed and are being published on Sectional Charts

along the coastal areas from Gulfport, Mississippi to Elizabeth City, North Carolina. The VFR Coastal Waypoints

Project, which has been enthusiastically endorsed by the

Aircraft Owners and Pilots Association (AOPA) and State

Department of Aviation representatives, has been selected

by the Government and Industry Aeronautical Charting

Forum to establish VFR waypoints as a unique navigational tool for VFR operations.

VFR waypoints have been developed to ease navigation

for VFR pilots using Global Positioning System (GPS) for

supplemental navigation; operating around, under, and

between airspace, which may require ATC clearance or

be restricted from their operation. These waypoints will

provide pilots with an additional tool to improve situational

awareness. VFR waypoints will allow pilots to fly from

point to point on sectional charts using pre-programmed

waypoints to avoid congested terminal areas or specialuse airspace.

Each VFR waypoint will be assigned a discrete non-pronounceable five-letter identification beginning with the

letters VP, which will be added to navigational databases for flight planning use. The waypoints will be depicted on sectional charts using the familiar Instrument

Flight Rules (IFR) waypoint symbol. VFR waypoints may

be collocated with a Visual Check Point, in which case

only the magenta flag will be depicted with the five-letter

identification. VFR waypoint identifications should not

be used in pilot/controller communications other than

those collocated with a Visual Check Point, where the

checkpoint name is used. VFR waypoints will also be listed

on the flap of the appropriate sectional chart and in the

Airport/Facility Directory (AFD).

VFR waypoints have been in use on terminal area charts

(TAC) and helicopter route charts in various parts of the

country since 1999. This is the first time they will be published on sectional charts. Sectional charts depicting VFR

waypoints will be New Orleans, Jacksonville, and Miami

with charting cycles after November 1, 2001. VFR

waypoints will be published on the Charlotte and Washington sectional charts in early 2002.
WAAS and Agricultural Aviation

By Shelby Wheeler, GPS TAC

In an August 24, 2000 press release, the Federal Aviation Administration announced the availability of the Wide Area Augmentation

System (WAAS) for some aviation and all non-aviation uses. The

21-day stability test that had been conducted prior to this declaration

demonstrated required system stability, allowing immediate use of

the WAAS signal by a broad range of users. WAAS continues to be

developed to provide the necessary integrity for the WAAS-required

safety-critical applications. Until the system design is completed and

initial operational capability is declared, the WAAS is not an approved source of aircraft navigation under instrument flight rules

(IFR), the release states.

However, WAAS is currently being used in many different applications, such as agriculture, surveying, marine application, military, and

data collection, just to name a few. WAAS has become an integral

part of its users guidance systems, and the agricultural aviation industry is no exception.

Satloc, a CSI wireless company, has been in the business of providing

guidance systems and differential GPS (DGPS) receivers for the past

nine years to markets all over the world, and is the leading provider of

DGPS guidance systems in the aerial application industry. Since the

beginning, Satloc has expanded into a number of other DGPS guidance markets, but aerial application is still a primary focus. We have

been providing receivers that use the WAAS signal to the industry

for over two years now, says Greg Guyette, Director of Sales (Air

Division) for Satloc/ CSI Wireless.

Satloc established its roots in the agricultural aerial applications field,

in which the GPS guidance market rapidly expanded after its introduction in 1992. DGPS guidance systems soared in popularity in this

community due to the markets willingness to try new technological

enhancements and their eagerness for efficiency in the work place.

The agricultural user has, indeed, tried numerous new technological

enhancements to improve aircraft guidance. Pat Kornegay, president of the National Agricultural Aviation Association (NAAA)

and 28-year veteran ag-pilot states, In the beginning, a locally transmitted differential source was used by ag-pilots, which entailed the

installation of a GPS receiver, computer system, and differential transmitter. Despite system accuracy, the limited range necessitated hundreds of stations across the country. Unfortunately, in many cases

each station was on a separate frequency, and a different band, so

aircraft were limited to a 40-mile operational radius. For operators

working multiple locations, it was necessary to install several receivers and pay several differential fees. In most cases the cost of differential service was in excess of $1000 per receiver per year

In 1995, the Coast Guard low frequency differential service became

available, and began its use by agricultural aircraft in areas where

transmitters were maintained. This service, although free, is limited

to areas in the vicinity of navigable waterways, and the low frequency band used is susceptible to electromagnetic interference from

thunderstorms. Since the operating aircraft might be as far as 100

miles from the transmitter, thunderstorm activity over any part of the

area surrounding the transmitter could cause loss of signal integrity,

says Mr. Kornegay.

Mr. Kornegay adds, Recently, several companies have begun transmitting differential correction information using satellites as signal

repeaters. This enables the agricultural aircraft operator to work

anywhere with one subscription, usually costing about $800 per year

per aircraft. The problem encountered with this service has been the

instability in the market, with several companies ceasing to exist, and

the discontinuation of the original C band system. These events

have caused operators to buy new receivers and change service companies on several occasions, sometimes resulting in revenue losses

when the changes occurred mid-season.

The advent of the WAAS system has finally given agricultural aviation a secure, stable system of differential correction that is available

throughout the United States. There are no annual fees associated

with its use, and the accuracy is excellent, says Kornegay. Truly this

has benefited many users. According to Ron Deck of Sky Tractor

Supply, a former NAAA official, WAAS is very important to the

users in the upper Red River Valley in North Dakota and Minnesota

because we are over 180 miles from the nearest 300khz tower; too far

to give us consistent accuracy. The paid subscription for most farm

users in the tight ag-market just isnt a viable choice.

WAAS acceptance in the agricultural aviation industry is strong,

according to Greg Guyette at Satloc. WAAS is an instrumental part

of most users guidance systems and without its continued use, there

would be some dramatic changes that would need to take place that

would be highly inconvenient and costly to todays ag pilot, he adds.

WAAS user satisfaction in the agricultural aviation industry is very

strong, for that matter. Dennie Stokes, an NAAA official says The

WAAS signal has been our most reliable source this year. As operators upgrade their equipment and purchase new GPS equipment, I

think WAAS will dominate the market. WAAS in my opinion is the

best source of GPS correction in the ag-industry.

Satloc has thousands of WAAS receivers in operation today and

nearly all feedback is positive. The accuracy of the WAAS with a

Satloc SLXg receiver has certainly proven to be highly accurate (submeter) and reliable. We have collected a great deal of data supporting this case, and we continue to monitor performance, says Guyette.

 The SLXg Receiver with WAAS is a part of many ag-users everyday necessities, he adds.

All of the primary manufacturers of DGPS equipment for agricultural aviation are currently offering WAAS receivers as standard

equipment. There have been no apparent problems with the system

and it has attained widespread acceptance throughout the industry,

says Pat Kornegay, adding, Approximately 90 per cent of all agricultural aircraft in the United States utilize DGPS guidance and a large

portion of them have converted to WAAS. In the very near future,

WAAS will probably become the primary source for ag-aviation, if it

has not already done so.

Industry Spotlight

3
4

Satellite NavigationHelping to Meet Environmental Requirements

By Joe Bellabona, GPS TAC / New England Region (ANE-520)

We are all aware of the extraordinary navigation capability of GPS. GPS has been the panacea to many aviation

navigation problems and the aviation community has aggressively applied this new technology in many ways. In

1998, the New England Region Air Traffic Division decided

to capitalize on the unprecedented accuracy of GPS. Aircraft departing RWY 27 at Logan International Airport in

Boston, MA, fly over highly populated areas of metropolitan Boston. In 1996, a Boston RWY 27 Environmental Impact Statement (EIS) Record of Decision (ROD) was signed

that directed RWY 27 departures to fly a specific ground

track to minimize noise to the underlying communities. The

ROD directed aircraft to track RWY heading to approximately 2 miles then turn left to track 235 degrees over

industrial areas and a designated green space located

southwest of the city. (See figure 1.1)

In addition to the 235-degree track identified in the ROD,

a capture corridor was designed to measure and monitor

flight track compliance. (See figure 1.2) This funnelshaped corridor was designed beginning with a throat just

1400 feet wide with an end point of 6300 feet wide. The

departure procedure requires a climbing aircraft to turn

approximately 35 degrees to hit a target just 1400 feet wide

several miles from the runway. This maneuver is difficult

to do even using outside visual ground references. This is

comparable to a precision approach ILS, where full-scale

deflection at the RWY end is just 700 feet wide, however

an aircraft on an ILS approach is stabilized with straight

in-course guidance.

Also, notice the series of lettered gates A through E. These

gates provide a means of measuring the progress of aircraft

within the corridor. The ROD requires that 68% of the

flight tracks pass through each of the corridor gates. This

type of accuracy is out of the reach of most conventional

navigational capabilities. In addition, ground based

Navaids are not conveniently aligned to provide course

navigation through the corridor. Therefore, a Vector Departure Procedure was initially utilized. Even after adjusting departure headings, the vector departure met with

limited success; what was needed was a navigational aid

to provide all weather capability to remain within the corridor.

The original WYLYY FMS Departure procedure was published in February 1998. This procedure provided the first

method to accurately navigate through the departure corridor in all weather conditions. Early results were less

than satisfactory. Many variables impacted the first FMS

procedure such as a Jeppesen waypoint coding error, pilot

technique, and aircraft with early FMS navigation equipment; non-SatNav. Each revision to the WYLYY has improved the operations of the procedure and compliance to

the ROD. Northwest Airlines (NWA) has been instrumental in helping to improve operations and compliance.

NWA briefed their crews on the importance of departure

compliance. In addition, NWA established pilot proceFigure 1.1

Figure 1.2
5

dures to arm their aircraft FMS lateral navigation (LNAV)

prior to take off then aggressively follow their flight director command bars. The results of a NWA study showed a

20 percent improvement in corridor compliance that almost

meets the ROD objectives of 68 percent compliance. (See

figure 1.3)

Since the WYLYY 3 has shown potential for full ROD compliance through all corridor gates and NWA recommendations for changes, the departure was revised and the WYLYY

4 was published on November 1, 2001. The WYLYY 4 Pilot

RNAV departure procedure is authorized for all E, F, and G

aircraft. The revised departure incorporates a NWA recommendation and a TARGETS modeling study to move

the first waypoint GARVY to help acquire greater accuracy for aircraft flying through the 1400-ft throat. The final

answer for improved noise abatement compliance is for all

operators to develop pilot procedures that mirror NWA operations. As all operators upgrade and equip with FMS

that have SatNav sensors, even greater accuracy can be

expected.

The success of the WYLYY FMS RNAV departure to enhance operations and noise abatement has paved the way

for Boston ATCT to design RNAV departure procedures

for all runways. The BEANN Town Departure has been

proposed as a single graphic departure design for all runways at Boston. This single graphic prototype is currently

under study by the Boston Procedures Office and will be

published after charting and automation issues are resolved.

When the BEANN Town Departure is published, then other

communities surrounding Boston Logan International Airport can benefit from the extraordinary navigation capability of SatNav.

The WAAS and PRN 22

By Bill Klepczynski, GPS TAC / WAAS Team (AND-730)

The basic premise for the existence of the WAAS is that

GPS, by itself, cannot promptly provide the information to

commercial air navigation users that a problem has occurred. On July 28, 2001 this conjecture was proven to be

true. At about 10:08 p.m. on July 28, the rubidium clock

on the GPS satellite designated as PRN 22 began to fail.

Failure of a clock on board a satellite is a matter of great

concern because it affects the ability of user navigation

sets to correctly determine their range to a satellite and,

consequently, their position.

A navigation receiver needs to measure or determine its

range to four different satellites in order to get a position

fix. A three-dimensional position fix yields latitude, longitude and altitude. The navigation receiver determines

its range to a satellite by measuring the offset of the clock

that is within the users receiver to each of the satellite

clocks to which it is measuring its range. It must be kept

in mind that each of the satellite clocks is a free-running

clock and has a unique offset and frequency that differs

from all the other clocks in the system. It is the task of the

GPS Master Control Station (MCS) to determine and

model the performance of each satellite clock with respect to some uniform time scale. In this case, the uniform time scale is GPS System Time. The parameters that

are used by the model to describe the performance of each

satellite clock with respect to GPS System Time are transmitted within the navigation message coming from each

satellite and used by the receiver to determine its range

to each satellite.

It is important to keep in mind that one of the errors that

contribute to the accuracy of a position fix is the ability to

correctly model the performance of a satellite clock with

respect to GPS System Time. The satellite clock governs

the transmission of the navigation message. The navigation message from each satellite must be transmitted on

time with respect to GPS System Time if the user is to

Figure 1.3
Figure 1.2

6

correctly determine its position. If a satellite clock goes awry and deviates from

its modeled performance, then the navigation message will not be transmitted on

time, resulting in an error in the user-determined position.

This is exactly what happened on July 28th:

The clock on the GPS satellite PRN 22

failed. Unfortunately, the failure occurred

in a region where the GPS MCS was not

able to monitor its performance and,

hence, update its model. However, the

WAAS was monitoring the performance

of PRN 22 and immediately started to

transmit corrections so the user could continue to use PRN

22 in its navigation solution. When the corrections exceeded the maximum value that it could transmit, at 10:14

p.m., the WAAS told its users to no longer use PRN 22 in a

navigation solution. Users were given the ability to use

PRN 22 for an extra 6 minutes before it no longer could be

used for a reliable position fix by a WAAS augmented receiver. The GPS MCS declared the navigation signal from

PRN 22 unusable at 11:58 p.m.

LAAS Testing at the

University of Oklahoma

By Dusty Somerville, GPS TAC / Flight Procedures Standards

Branch (AFS-420)

Since August 2001, the University of Oklahoma (OU) has

been conducting Category A and B flight-testing of LAAS.

Their mission is to provide flight test data to support Minimum Operational Performance Standards (MOPS) and procedure criteria development by AFS-420.

This is a cooperative effort between the

Department of Aviation, which operates

the test aircraft, and the Department of

Electrical and Computer Engineering,

which is responsible for conducting the

tests, collecting the data, and analyzing

the results. Dr. John Fagan, world-renown for his work with solar-powered and

battery-powered cars, directs a team of

graduate students who conduct the testing.

The approach and departure procedures

are primarily flown at Max Westheimer airport in Norman, Oklahoma (See Figure

1.1) where an airfield has been configured

with three LAAS receiver stations. (See

Figure 1.2) Dr. Fagan and his team have

used their solar car experience with solar

cells and high performance batteries to develop very unique LAAS stations. Unlike

other hard-wired LAAS systems, these stations are battery/solar powered and self-contained. These

low cost LAAS stations avoid the expensive installation

costs associated with providing power and communications capability to remote locations around an airfield. A

simple concrete pad for each LAAS receiver station is the

only airfield preparation required.

Conducting these tests at OU has some significant advantages. OU instructor pilots fly OU-owned aircraft at a

bargain price. The close proximity to the Mike Monroney

Aeronautical Center in Oklahoma City allows AFS-420

personnel to supervise the flight-testing and analysis conducted at OU.

Although the testing is designed to collect data on flight

technical error and navigation system error for use in establishing TERPS standards, experience with this leading

edge technology has yielded many other benefits.

OU students and faculty have gained valuable expertise

in satellite navigation systems, particularly GPS precision

approaches since they began WAAS

flight-testing in 1997. Lessons

learned from WAAS testing have

been applied to ongoing LAAS tests.

They also perform the initial data

analysis so they can quickly identify

trends or testing problems in accuracy, integrity, or availability. Test

adjustments can be made after meetFigure 1.1
ings with FAA personnel to review the preliminary test results.

Because OU is exclusively conducting Category A and B

testing under typically windy Oklahoma flying conditions,

they are in a unique position to evaluate the effects of turbulence in light airplanes on satellite navigation systems.

Additionally, these tests provide critical feedback on the

human factors of a single pilot conducting a SatNav approach in a light aircraft.

Category A tests are flown in a Piper Seneca, while Category B tests are flown in a Rockwell Turbo Commander. A

low cost LAAS Gamma Navigator is combined with LAAS/

WAAS Multi-Mode Receiver and Ashtech truth system (a

system that uses a Z-12 GPS-based precision surveying instrument, utilizing two receiversone on the ground at a

precisely surveyed location and the other in the aircraft

to record precise differential GPS signals which are then

processed post-flight to determine the exact position of the

aircraft with extreme accuracy). This test equipment has

been mounted into a portable rack that allows quick equipment installation into either aircraft.

OU testing has already resulted in significant improvements

to SatNav procedures, equipment, and specifications. For

example, their experience with small aircraft undergoing

rapid position changes led to a change in MOPS from a 1

Hz update rate to 5 Hz. They have developed statistical

models that have been transferred to the FAA for incorporation into the Airspace Simulation and Analysis (ASAT)

for TERPS model, which is a high fidelity computer simulation, run by engineers in AFS-420. This models various

aviation scenarios, and is used to examine the risk factors

of various approach configurations. OU personnel are also

in a unique position to work with manufacturers to identify

and correct any potential equipment hardware or software

problems.

These tests have laid the groundwork for low-cost LAAS

installations worldwide, and have the potential to add precision approach capability to hundreds of airports and thousands of aircraft throughout the United States and abroad.

For more information, please visit http://terps.faa.gov and http:/

/www.ashtech.com/.

RNAV Route Development

By Bob Brekke, GPS TAC / Western Pacific Region (AWP-520)

The Western-Pacific and Northwest Mountain Regions

have developed twenty-one Area Navigation (RNAV) offairway direct routes between key cities. The cities include Seattle, Portland, and Vancouver in the Pacific

Northwest, and Los Angeles, San Francisco, San Jose,

Oakland, Ontario, Palm Springs, John Wayne-Orange

County, Las Vegas, and Phoenix in the Western-Pacific

Region. The RNAV routes were developed in conjunction with Alaska Airlines as the lead carrier and the Western-Pacific and Northwest Regional National Airspace

Review (NAR) Teams and Air Traffic Control Facilities.

The objective of these routes is to provide a seamless RNAV

departure, en route, and arrival between the selected airports for all appropriately equipped RNAV aircraft. Annual savings, provided by Alaska Airlines, are projected

to approach more than $800,000.

This is an on-going effort that will continue in the Northwest and Western-Pacific Regions to provide all RNAVequipped aviation customers with the benefits of this GPS

technology.

General Comments on

the Characteristics of

Test And Evaluation of

Augmented GPS for NAS

By Barry Billmann, FAA William J. Hughes Technical Center

(ACT 360)

GPS/WAAS/LAAS implementation and utilization in the

NAS involves gathering information on the performance

and perceptions of the aviation industry pilot regarding

the new system. Total system performance evaluation must

involve the pilot in the evaluation process and address

these issues:

4 Pilot assessment of the flyability of the new system.

7
4Pilot assessment of performance deviations from ex

isting systems.

Note: WAAS will provide four levels of approach service, versus the established standard of two levels of

service (precision and non-precision). These additional

levels of service will provide a better fit of Standard Instru

ment Approach Procedure (SIAP) development to air

ports and heliports with existing SIAPs and enable the

FAA to provide IFR capability to airports/heliports that

do not now have IFR service. However, new procedure

charting concepts must be evaluated, such as depiction of

distance to threshold with LAAS. Also, system require

ments to support an entire new repertoire of cockpit an

nunciations must be evaluated.

4Pilot assessment of the workload associated with the

new navigation system.

4Pilot assessment of the safety associated with the

new approach procedures.

If the appropriate avionics are not available or the pilot

perception and performance issues are not addressed, there

is no commissioning of the system.

In order to address both pilot and procedure factors, compliant or near Minimum Operational Performance Standards

(MOPS) compliant avionics must be available. With GPS,

and it augmentations, much more of the system processing

is the responsibility of the airborne avionics than with classical navigation systems. For example, ILS provides a signal-in-space, which airborne avionics systems use as is.

However, for GPS (even unaugmented), the avionics must

evaluate the usability of the signal-in-space by applying

Receiver Autonomous Integrity Monitoring (RAIM) and/

or Aircraft Autonomous Integrity Monitoring (AAIM) techniques. With GPS system augmentation (WAAS & LAAS),

the burden of determination of system usability is significantly increased beyond basic GPS. For instance, WAAS

avionics must evaluate the signal-in-space and determine

what type of one of four procedures may be flown. LAAS

avionics must support a procedure selection process that is

different than tuning an ILS and requires interaction with

the LAAS ground facility.

Experience has shown that the development and acquisition of compliant avionics must be done in cooperation with

industry. Avionics must be available to validate WAAS

and LAAS system performance during Developmental Test

and Evaluation (DT&E) and Operational Test and Evaluation (OT&E). An example when this philosophy was

not used and the resulting negative impact on the system

deployment, is presented below. Additionally, examples of

the application of the philosophy and the benefits to the

Program are cited, as well.

An Example Where We Waited for Industry to Produce

Certified Avionics

It was agreed to wait for the first TSO C129 receiver to be

certified prior to starting TERPS data collection for GPS

non-precision approach operations, since the GPS signal

in space was already well established and being used without augmentation. However, when testing began, the avionics were totally incapable of supporting test requirements. The following deficiencies existed in certified

equipment:

4 The sensor could not provide adequate guidance

on a T procedure

4 Leg segment switching logic did not provide usable

guidance at waypoint transitions

4 Departures were in the database and could be flown,

but terminal operation integrity was not met

4 The sensor could not fly an arc overlay procedure

These problems required the manufacturer to issue service bulletins resulting in a significant delay and substantial cost increase to the program. Other sensors that were

certified, at the time, had significant human factors issues

associated with control and display. The FAA system safety

goal requires that such issues be addressed before commissioning.

Benefits that have been Derived when Avionics Development was Undertaken in Cooperation with Industry

With both WAAS and LAAS, funding has been provided

to acquire near MOPS compliant avionics to support the

activities mentioned above. It must be noted that the avionics standards do not exist in a vacuum. With both WAAS

and LAAS, the FAA is fielding systems to augment the

GPS constellation and control segment. Near MOPS com8
pliant avionics testing has resulted in numerous changes,

not only to the avionics standards, but also to the augmented

system standards under test. In many cases, such as with

message types 0, 1 and 27, the required changes were system changes; not just avionics changes.

Cooperative avionics development permits the FAA to collect representative flight test data enabling procedure design criteria to be available for commissioning. The biggest

impact is the availability of avionics for flight inspection.

Without certified avionics there is no flight inspection to

support commissioning. Without flight inspection there is

no commissioning.

Global Positioning

SystemApproach Minima

Estimator(GAME)

By Dr. S. Vincent Massimini, MITRE Corporation

The MITRE Corporations Center for Advanced Aviation

System Development (CAASD) has developed a software

capability that assesses the benefits of potential instrument

approach procedures. The goal of the GPS (Global Positioning System) Approach Minima Estimator (GAME) is to

provide insight into the impact of approach design criteria

on the expected minima at thousands of runway ends.

Instrument approach procedures are designed according to

Federal Aviation Administration (FAA) criteria. New systems, like the FAAs GPS Wide Area Augmentation System

(WAAS), have opened the way for new thinking about the

criteria for approach design. For example, the initial WAAS

procedures will provide a lateral/vertical navigation (LNAV/

VNAV) instrument approach capability, equivalent to that

which is available from qualified baro-VNAV systems that

use unaugmented GPS for lateral navigation and barometric altimetry for vertical navigation. However, the LNAV/

VNAV approach design criteria do not take advantage of

the improved horizontal accuracy and integrity of the initial WAAS (relative to unaugmented GPS). So, the way is

open to define new criteria with potentially better minima.

GAME uses databases of terrain, obstructions, and runway

configurations to estimate the height above-touch down

(HAT) for a future approach, based on actual or postulated approach design criteria. GAME then uses an airport infrastructure database, in conjunction with the HAT

and the aircraft approach category, to estimate the visibility minimum for the approach. This process can be repeated for thousands of runway ends to compute the statistics of the HAT and visibility minima, and to compare

them with the statistics of minima resulting from other

approach design criteria, thus obtaining valuable insight

into the impact of design criteria on airport access benefits. Current GAME capabilities include LNAV (nonprecision RNAV approaches), LNAV/VNAV, Instrument

Landing System/Wide Area Augmentation System/Local

Area Augmentation System (ILS/LAAS/WAAS) Category

I, and several approach types that are still being developed by the FAA.

Navigation Workshop

By Carol Wheeler, ANN TAC (AND-700)

The FAA Navigation Integrated Product Team (IPT),

AND-700, opened the first National Navigation Community Workshop in San Antonio, Texas on Monday, September 10 with registration beginning at 4:00 pm,. A reception followed registration, which provided two hours

of time for team members to renew acquaintances and

meet new members. A total of 196 members of the National Navigation Community attended the workshop.

The first day of the workshop was a General Session, including all workshop participants. The Navigation Integrated Product Team Lead, Jack Loewenstein, and IPT

Staff Dennis Kolb made introductory and welcoming remarks. A new video titled The FAA, Proudly Serving

the Air Navigation Community was shown and received

an enthusiastic response. The credits, for the excellent

production of this video, go to Mary Ann Davis, GPS TAC,

and Bill McDonald, ASU-400. The day continued with

several outstanding speakers.

Mr. Gerald Lavey, Executive Assistant to the FAA Administrator for Internal Communications was the keynote

speaker. Mr. Lavey has over 27 years service with the FAA

and is highly respected within the community for his forth9
right style of communicating and reporting the agencys

activities. He provided examples of successes made by the

dedication and hard work of the agencys personnel that

does not get recognition in the press. He accurately outlined the challenges faced by the FAA to perform a monumental task with limited resources and acknowledged some

things could always be improved upon. He further stressed

the importance and need for diverse thinking, and warned

not to allow preconceptions to stifle unification or creativity. Last, he advised that knowledge management and

proper communications give people the power to operate

successfully and solve problems. As he left the podium he

received a resounding thunder of applause and a standing

ovation from the team.

Dr. Therman Evans, founder and CEO of WholeLife Associates, was the workshop motivational speaker. Dr Evans

received his M.D in 1971 from Howard University and is

the recipient of several honors, recognitions, and awards.

Dr. Evanss principle message centered on wellness, stress

management, and dealing with change, which could not

have been more timely with the horrific events that were

unfolding in New York and Washington, D.C. that morning. Some of the quotes and key points from Dr. Evans

inspirational talk include Blessed are the flexible for they

shall never be bent out of shape, talk does not cook rice,

you cannot change where you are unless you change what

you do, nobody wants to be sick, but we choose the things

that make us sick, and people do not like change, even if

its better for us; yet in the course of natural human life,

everything changes. These quotes quickly summarize a

wonderfully detailed explanation of the impact of stress on

our physical and emotional health and therefore the enjoyment of our work and play. Dr. Evans is a huge proponent

for taking time to play, in the midst of managing multiple

responsibilities: Good words to remember!

Also on the agenda for the first day were Claire Robinson,

AOZ-500, who provided an overview on the on the NAS

Operational Evolution Plan (OEP); Bob Wright, AFS-400,

spoke on the Future of Navigation; Jack Nager, ANI-1,

and Trevor Henry, ARN-200, addressed ATS Challenges

Today and in the Year 2010; and Nelson Spohnheimer gave

an excellent overview on the State of Navigation, A Regional Perspective.

On Wednesday, September 12, all participants selected

one of four working sessions to attend. The four sessions

were divided into Policy, General Issues, Technical

and Satellite Navigation. Each session was lead by a

facilitator using a prepared agenda of topics to be briefed

and discussed. The agenda for each session was built from

the issues recorded and compiled from the Navigation team

visits to the FAA Regions and Centers earlier this year.

Action items, agreements and significant discussion items

were noted during the sessions and compiled into a report

to the entire group on the last day of the session.

The Deputy Navigation IPT Lead, Harry Kane closed the

workshop on September 13. Harry provided a comprehensive summary of the accomplishments made during the

workshop and thanked everyone for their participation and

the hard work done to make the workshop a success.

Each participant that attended the workshop will receive

a compact disc (CD) that includes a copy of the video

seen at the opening of the Workshop, a copy the briefings,

both from the General Session and the Working Groups,

minutes and action items taken from each of the four working groups, participant list, and candid photographs covering the three days of the workshop.

Code-Carrier Coherence

(CCC) Monitor

By Bill Klepczynski, GPS TAC / WAAS Team (AND-730)

The navigation signal coming from the GPS satellites

has three components; the carrier wave (its phase and

frequency), the tracking codes (called pseudo-random

noise [PRN] codes) and the navigation message. Information on the satellites position is contained in the navigation message. The PRN code allows the user to determine the range to a satellite. With the data contained in

the navigation message, users can determine their position if the range to four satellites is measured. Some receivers use the phase of the carrier to improve the accuracy and precision of the computed range. As one can

imagine, the process by which a position is computed is a

complex one. There are many factors that can influence

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the derived user position, including the properties of the

atmosphere through which the GPS signals travel, the characteristics of the various hardware components within the

GPS satellite and the user receiver, as well as the nearby

surroundings of where the user receiver is located. Some of

these errors can be overcome or mitigated by the differential GPS process. However, some cannot because they are

unique to the user and the reference station.

The WAAS Integrity Performance Panel (WIPP) has been

dealing with two separate effects that could surreptitiously

degrade the accuracy of the WAAS if not properly handled.

Analysis has shown that it is possible to determine their

presence with one algorithm (procedure) and take appropriate action to mitigate their effects. This algorithm is

called the Code-Carrier Coherence (CCC) Monitor and

reports potential errors to the user in the form of the User

Differential Range Error (UDRE) broadcast by the WAAS.

Before going into the problems, a very brief explanation of

how a receiver works might be useful. Within every GPS

spacecraft, there is a local oscillator (clock), which generates the frequency that gets multiplied up to the transmitted frequency. There is also equipment that generates the

PRN code for each satellite through a device called a

correlator. That code and the navigation data for that satellite are impressed on the transmitted signal. Thus, there

is a relation between the PRN code and the phase of the

carrier frequency of the transmitted signal. The user receiver has similar equipment that generates a PRN code

and compares it with the received code. Through information contained within the navigation message the user receiver can determine the time at which the code left the

satellite and compare it with the time of its local clock and

determine the travel time of the signal and, hence, the

range to the satellite. However, this range is not the actual

range to the satellite because many systematic effects affect it. These systematic effects must be taken into account before the true range can be derived from this socalled pseudo-range.

The first problem that affects the accuracy of ranges to GPS

satellites deals with code-carrier divergence. Code-carrier divergence is a change in the relationship between the

PRN code and the phase of the carrier frequency. In theory

it should remain constant, but there are reasons why it could

change. The passage of the signal through the ionosphere

will cause a shift because the ionosphere is a dispersive

medium, but this phenomenon can be modeled. Multipath, the reception of a reflected signal by the user receiver, will also cause this phenomenon, but this error is

dependent on the location of the users receiver. Multipath manifests itself by a shift in the code-carrier phase

relation from its original one.

The second problem is called the SV19 Problem. In March

1993, a GPS satellite, designated as SV19, transmitted an

anomalous signal (sometimes called an Evil Wave Form)

that caused an error in the estimated ranges to that satellite to vary between 3 to 8 meters in differential GPS systems. Two instrumental problems can cause this error.

First, the correlator in the satellite developed a minor glitch

that caused some parts of the PRN code to be elongated

and some to be shortened. Second, the spacecraft correlator

uses a different correlator spacing than the correlator in

the user receiver. Any discrepancies or perturbations in

the PRN code sequence will affect the users determination of the range to the satellite. Upon further investigation, it was apparent that, while this was the one and only

known instance that such an error was observed, the satellite design is such that it is possible that it could occur

again. This problem also manifests itself in a shift of the

code in the receiver correlator with respect to the original

carrier phase.

The CCC algorithm looks at the difference between the

phase and code of a signal from a GPS satellite obtained

from all the WRE receivers tracking that satellite at the

same instant. It then forms a weighted average of the

deviations for all the receivers viewing the satellite. If

there is code-carrier coherence, i.e., no change in the

relation between code and carrier, the average should be

near zero. In the presence of incoherence or divergence,

the result will be non-zero and this number will represent

an error in the pseudo-range. It means that multi-path or,

possibly, the SV19 problem affects one of the WRE receivers. When this happens, the UDRE is bumped higher for

that satellite to reflect the fact that there is a larger potential error associated with this satellite. The CCC algorithm doesnt necessarily know what caused the larger

error, code-carrier divergence or the SV19 problem, but it

knows that something is wrong with the estimate for the

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range for that satellite and lets the user know through a

Dont Use UDRE value.

New Special Copter RNAV

Approaches and Departure

Procedures Under

Development In California

By Bob Brekke, GPS TAC / Western Pacific Region (AWP-520)

New Special RNAV Helicopter Instrument Approach and

Departure Procedures, developed by Satellite Technology

Implementation, L.L.C. (STI), a non-federal source, and

approved by FAA, are in the final stages of coordination.

These GPS-based procedures are Special RNAV COPTER

approaches and departures to various hospital heliports in

Northern California for a single-helicopter operator and are

not charted for the public.

In total, there are six Special COPTER RNAV Approach

Procedures and six Special COPTER RNAV Departures

Procedures in development that will serve area hospital

heliports in the Sacramento Terminal Radar Control

(TRACON), Stockton TRACON, and Oakland Center

area.

GPS-based enhancements will continue to be developed in

the Western-Pacific Region for the vertical flight community, so that the benefits of this technology can be realized

by all RNAV equipped Rotorcraft operators.

Results of Early LORAN-C

Modernization Testing

By Mitch Narins, Systems Engineering (AND-702)

The LORAN-C navigation system, developed by the U.S.

Department of Defense (DoD), has been operated by the

U.S. Coast Guard since the 1950s. Initial installations were

primarily outside the continental U.S., but by the early

1970s, the Coast Guard had determined the LORAN-C

system should be used as a federally provided maritime

navigation system throughout the coastal areas of the

United States. The system was expanded to provide coverage in the coastal waters of the continental U.S. and

Alaska.

Interest by the Federal Aviation Administration (FAA)

led to additional installations that provided coverage

throughout the continental U.S. Through the mid- to

late-1980s the FAA also undertook the development of

requirements, procedures, and ground system support to

allow certification of LORAN-C system for use in the nonprecision approach phase of navigation. Initial attempts

by user equipment vendors to achieve aviation certification disclosed the need for significant hardware and software improvements that primarily involved the need for

improved aircraft antenna systems and advanced receiver

processing to take advantage of all available LORAN-C

signals. These and other related problems produced shortcomings in the availability and continuity of service

parameters of the certification requirements.

Despite the lack of certification, there was widespread

use of VFR LORAN-C in the general aviation community through the mid-1990s. However, as the Global Positioning System (GPS) began to mature, users found a comparable niche for this new system and a migration from

LORAN-C began. The migration was accelerated when

the U.S. Government announced in its 1994 Federal

Radionavigation Plan (FRP) plans to terminate LORANC in the year 2000.

Following the 1994 FRP announcement, support to continue LORAN grew from some groups within the aviation

community that resulted in directions from the U.S. Congress, via the budgetary process. This resulted in the 1999

FRP announcement that LORAN services would continue

in the short term, while the merits of its long-term operation are evaluated. Over the past several years, Congress has continued to provide substantial LORAN-C

funding to the Federal Aviation Administration (FAA)

($25M in FY 01) and has requested it to continue the

development of LORAN.

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In compliance with these Congressional mandates, the FAA

initiated a LORAN-C evaluation program to determine

whether LORAN could benefit aviation, and if so, by what

means. While LORAN-C currently can be used as a secondary navigation system in both terminal and enroute environments, it does not support the approach phase of flight.

The FAA established an Interagency Agreement with the

U.S. Coast Guard (USCG), the operators of the LORAN

system, and formed an evaluation team to help determine

whether LORAN would be capable of providing lateral

navigation (RNP.3) services to the National Airspace System (NAS) and/or other ancillary capabilities.

The FAAs Wide Area Augmentation System (WAAS) is

the means by which differential GPS corrections will be

provided to aircraft operating in the NAS to support both

lateral (LNAV) and vertical (VNAV) navigation. The

current WAAS architecture includes geostationary satellites, which transmit differential correction messages to aircraft at L-band frequencies. WAAS messages are currently

transmitted on the GPS L1 frequency for non-safety related services via two leased INMARSAT geostationary

(geo) satellites. It has always been known that the combination of high angles of elevation, or look angle, in some

northern areas of the NAS in combination with high terrain elevation could cause masking of the WAAS geo signal. So, many alternatives are currently under investigation to solve this problem.

LORAN is one of those alternatives that are being studied

to solve this masking issue. LORANs significant coverage

of the NAS (see Fig. 1), its robust signal (400  1600 kW)

and its diverse spectrum (between 90 kHz and 110 kHz),

made it attractive for further exploration.

The problem  how could LORAN transmit the entire

WAAS message at the 250 bit/second rate without significant modification of the signal specification and, thereby,

denial of service to existing legacy sers?

The FAA Navigation IPTs System Engineering Office and

the U. S. Coast Guard LORAN Support Unit (LSU), in

cooperation with Stanford University, are developing an

enhanced LORAN-C Communications capability for Global Positioning System (GPS) integrity, and potentially for

GPS correction data. The LORAN Recapitalization

Project LRP is a multi-year FAA/USCG initiative to modernize the U.S. LORAN-C system to meet present and

future radionavigation requirements while leveraging

technology and funds to optimize operations, support and

training, and reduce total cost of ownership.

Very early analysis of the testing in Alaska appears to show

that transmission of WAAS data via LORAN at the required 250 b/s is feasible and that use of all-in-view receivers and H-field antennas are promising mechanisms

to allow LORAN to support lateral navigation within the

NAS. Although showing promise, much more work must

be done before LORAN can be considered for broadcasting the WAAS corrections in areas that cant receive the

WAAS corrections via the WAAS geos.

Stay tuned for further developments. For more information on

this research, including the current status of this project, please

visit http://www.uscg.mil/hq/lsu/webpage/projects.htm,

choose the desired time period, and reference the FAA34: LORAN DATA CHANNEL COMMUNICATIONS project.

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Figure 1  Loran C

Navigation Coverage
The Lighter Side

Federal Aviation Administration

800 Independence Avenue, SW

Washington, DC 20591

http://gps.faa.gov

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