Air OperationsAir OperationsBranch Director CourseBranch Director Course

Navigation Navigation Fundamentals Fundamentals

& Understanding & Understanding GPS for Sortie GPS for Sortie

PlanningPlanningU.S. AIR FORCE

AUXILIARYU.S. AIR FORCE

AUXILIARY

Goals for understandingGoals for understanding

Prepare mission staff to be able to plan and brief Prepare mission staff to be able to plan and brief missions that can be executed efficiently and missions that can be executed efficiently and conveniently with our equipmentconveniently with our equipment– Navigation fundamentalsNavigation fundamentals– Capabilities and limitations of GPSCapabilities and limitations of GPS– Capabilities of Apollo GX55 GPS units in Minnesota Capabilities of Apollo GX55 GPS units in Minnesota

Wing aircraftWing aircraft– What information is needed to program the GPS unit What information is needed to program the GPS unit

for search patternsfor search patterns– What can and cannot be programmed in the GX55What can and cannot be programmed in the GX55– What can be “improvised”What can be “improvised”– Learn about the “gotchas” using GPSLearn about the “gotchas” using GPS

PART 1PART 1Navigation fundamentalsNavigation fundamentals

Latitude and longitudeLatitude and longitude

Describing directionsDescribing directions

LatitudeLatitude

Parallels Parallels

Measure How Far Measure How Far North or South of North or South of EquatorEquator

Zero Degrees is Zero Degrees is EquatorEquator

““90 Degrees North” is 90 Degrees North” is the North Polethe North Pole

““90 Degrees South” is 90 Degrees South” is the South Polethe South Pole

North Latitudes

South Latitudes

Equator

LongitudeLongitude

Half Great Circles Intersecting at the PolesHalf Great Circles Intersecting at the Poles

Measure How Far East or West of EnglandMeasure How Far East or West of England

Zero Degrees is Prime Meridian (England)Zero Degrees is Prime Meridian (England)

Numbers between 0 and 180 are either East or Numbers between 0 and 180 are either East or West LongitudeWest Longitude

180 Degrees is opposite side of globe from England 180 Degrees is opposite side of globe from England – near international date line in Pacific Oceannear international date line in Pacific Ocean

East LongitudeEast LongitudeWestWest LongitudeLongitude Prime Meridian

LongitudeLongitude

Latitude and LongitudeLatitude and Longitude

• Latitude is Based Latitude is Based on Earth’s motionon Earth’s motion• Axis of rotation Axis of rotation

defines poles defines poles and Equatorand Equator

• Longitude is Longitude is ArbitraryArbitrary• Greenwich, Greenwich,

England was England was chosenchosen for ‘prime for ‘prime meridian’.meridian’.

Where’s Minnesota?Where’s Minnesota?

Twin Cities Twin Cities – Northern Minneapolis is at Northern Minneapolis is at

45 Degrees North (half 45 Degrees North (half way between the Equator way between the Equator and North Pole!)and North Pole!)

– 93 Degrees West is 93 Degrees West is roughly the Eastern edge roughly the Eastern edge of St. Paul.of St. Paul.

The Northwest corner of The Northwest corner of the state:the state:– Exactly 49 Degrees NorthExactly 49 Degrees North– Roughly 97 Degrees WestRoughly 97 Degrees West

How Big is One Degree?How Big is One Degree?

Degrees of Latitude are always the same Degrees of Latitude are always the same distance apart, about 60 Nautical Milesdistance apart, about 60 Nautical Miles

Degrees of longitude vary in distance – Degrees of longitude vary in distance – near the poles the lengths are quite small.near the poles the lengths are quite small.– In Minnesota, a degree of longitude is about In Minnesota, a degree of longitude is about

40 to 44 Nautical Miles across40 to 44 Nautical Miles across

Dividing Degrees into Smaller UnitsDividing Degrees into Smaller UnitsA ‘Minute’: 1/60A ‘Minute’: 1/60thth of a Degree of a Degree – roughly a mile in sizeroughly a mile in size

Minutes are usually broken down into Minutes are usually broken down into tenths of minutestenths of minutes– Alternatively, a ‘Second’ is 1/60Alternatively, a ‘Second’ is 1/60 thth of a minute of a minute

Expressing Latitude and Longitude Expressing Latitude and Longitude in Degrees and Minutesin Degrees and Minutes

Small high circle after number denotes Small high circle after number denotes degrees degrees

Apostrophe after number denotes minutesApostrophe after number denotes minutes

Example:Example: Minneapolis Flying Cloud Airport Minneapolis Flying Cloud Airport4444o o 4949..6363’ ’ N 93N 93o o 2727..4343’ ’ WW

read as…read as…44 degrees 49.63 minutes North 44 degrees 49.63 minutes North 93 degrees 27.43 minutes West93 degrees 27.43 minutes West

Expressing Latitude and Longitude Expressing Latitude and Longitude in Degrees, Minutes, and Secondsin Degrees, Minutes, and Seconds

A double-quote after a number denotes A double-quote after a number denotes secondsseconds

Example:Example: Minneapolis Flying Cloud Airport Minneapolis Flying Cloud Airport4444oo 4949’’ 37.8 37.8”” N 93 N 93oo 2727’’ 25.8 25.8”” W W

read as…read as…44 degrees 49 minutes 37.8 seconds North 44 degrees 49 minutes 37.8 seconds North 93 degrees 27 minutes 25.8 seconds West93 degrees 27 minutes 25.8 seconds West

Determining Coordinates from a Determining Coordinates from a ChartChart

Expressing Direction: Expressing Direction: The Compass RoseThe Compass Rose

360

N

90270

180

330 30

210

120

60

150

300

240S

W E

Directions are expressed as a number from 001 to 360

Magnetic VariationMagnetic Variation

The Magnetic North The Magnetic North Pole is located in Pole is located in Canada, not at the Canada, not at the True North Pole.True North Pole.

The difference in The difference in direction between the direction between the two poles is two poles is measured and measured and referred to as referred to as magnetic variationmagnetic variation

Magnetic Variation in the Magnetic Variation in the USUS

-15-15ºº-10-10ºº -5-5ºº 00ºº

+5+5ºº +10+10ºº+15+15ºº

Agonic LineAgonic Line

Easterly VariationEasterly Variation

Westerly VariationWesterly VariationNote: These lines move over the years because the magnetic north pole is in motion

+20+20ºº

PART 2 - GPS PART 2 - GPS Overview of GPS for SAROverview of GPS for SAR

– MotivationMotivation– Potential uses for SARPotential uses for SAR– How it worksHow it works– AccuracyAccuracy– Limitations and GotchasLimitations and Gotchas– TerminologyTerminology

Describing search patterns for the GX-55Describing search patterns for the GX-55ImprovisingImprovising

MotivationMotivationGPS is a GPS is a powerfulpowerful tool for search and rescue tool for search and rescue– Allows very precise search patternsAllows very precise search patterns– Makes manageable what would otherwise be very Makes manageable what would otherwise be very

difficult patternsdifficult patternsExpanding square at any angleExpanding square at any angleCreeping line along a courseCreeping line along a courseOffset route searchesOffset route searchesGrid searches over indistinct terrainGrid searches over indistinct terrain

– GPS should be our primary tool for Search and GPS should be our primary tool for Search and Rescue navigationRescue navigation

GPS is of course also very handy for general GPS is of course also very handy for general navigationnavigation

Potential uses of GPS for Potential uses of GPS for Air and Ground SAR Air and Ground SAR

Getting to/from a search area Getting to/from a search area – Going to a location designated on a mapGoing to a location designated on a map– Going to a site identified by another SRUGoing to a site identified by another SRU

A ground team going to a site previously A ground team going to a site previously identified by an aircraftidentified by an aircraft

Navigation while conducting a search Navigation while conducting a search patternpattern

Clue logging (and re-finding)Clue logging (and re-finding)

GPS for SAR: GPS for SAR: Potential advantagesPotential advantages

More flexible search area partitioningMore flexible search area partitioning

More accurate loggingMore accurate logging

More accurate search linesMore accurate search lines

Easier and more accurate communication Easier and more accurate communication of location informationof location information

Other GPS SAR UsesOther GPS SAR Uses

Electronic distress signalsElectronic distress signals– PLBs PLBs

– Personal locator beacons– Personal locator beacons– ELTs ELTs

– Emergency locator transmitters– Emergency locator transmitters– EPIRBs EPIRBs

– Emergency Position Indicating Radio Beacons– Emergency Position Indicating Radio Beacons

New 406 MHz digital beacons sometimes New 406 MHz digital beacons sometimes transmit GPS coordinatestransmit GPS coordinates– GPS then becomes a tool for both the rescuer and GPS then becomes a tool for both the rescuer and

the rescuedthe rescued

How it Works – The BasicsHow it Works – The Basics

Spaced-based system Spaced-based system (unlike Loran or VOR)(unlike Loran or VOR)

‘‘Constellation’ of 24 satellites in Constellation’ of 24 satellites in six orbital planessix orbital planes– 21 active satellites 21 active satellites

plus 3 operating sparesplus 3 operating spares– In “High” orbit of about In “High” orbit of about

12,000 miles12,000 miles– Each circles the Earth about Each circles the Earth about

every 12 hoursevery 12 hours

How it Works – The BasicsHow it Works – The Basics

GPS satellites transmit informationGPS satellites transmit information– ““Pseudo-random” code with time informationPseudo-random” code with time information– Satellite orbital position data Satellite orbital position data

““Almanac” dataAlmanac” data

““Ephemeris” data Ephemeris” data

– Updated atmospheric modelsUpdated atmospheric models

GPS receiver uses this data to figure out GPS receiver uses this data to figure out what time it is and what time the signals what time it is and what time the signals were sentwere sent

How it Works – The BasicsHow it Works – The Basics

GPS receiver measures distance to satellites by GPS receiver measures distance to satellites by determining the amount of time that the radio determining the amount of time that the radio signal takes to travel from each satellitesignal takes to travel from each satelliteEach distance measurement effectively defines a Each distance measurement effectively defines a sphere around a satellitesphere around a satelliteMultiple satellites must be used to determine a Multiple satellites must be used to determine a positionposition– Given two satellites, two sphere intersect to determine Given two satellites, two sphere intersect to determine

a circlea circle– Given three satellites, a sphere and a circle intersect to Given three satellites, a sphere and a circle intersect to

determine two pointsdetermine two points– A fourth satellite can determine a positive 3D positionA fourth satellite can determine a positive 3D position

AccuracyAccuracy

A complex questionA complex question– DOD has a 66 page document DOD has a 66 page document

describing the performance of GPS describing the performance of GPS Standard Positioning Service (SPS)Standard Positioning Service (SPS)

The short story The short story – Garmin states that their GPS receivers Garmin states that their GPS receivers

“are accurate to within 15 meters on “are accurate to within 15 meters on average”average”

– Typically about 6 to 12 Meters accuracy Typically about 6 to 12 Meters accuracy can be seencan be seen

AccuracyAccuracy

Accuracy and reliability is actually a complex Accuracy and reliability is actually a complex subject. There are many factors that can subject. There are many factors that can impact system.impact system.– Receiver errorsReceiver errors– Atmospheric (ionosphere) errorsAtmospheric (ionosphere) errors– Solar activity (sun spots and solar storms)Solar activity (sun spots and solar storms)– Location of receiver Location of receiver

(some parts of the Globe get better coverage than others)(some parts of the Globe get better coverage than others)– Orbital errors (inaccuracies in the reported orbital position)Orbital errors (inaccuracies in the reported orbital position)– Poor satellite geometry (satellites lined up or bunched up)Poor satellite geometry (satellites lined up or bunched up)– Limited number of satellites in viewLimited number of satellites in view– Satellite malfunctions (or satellites taken out of service)Satellite malfunctions (or satellites taken out of service)– ““Multi-path” errors (radio signal reflections)Multi-path” errors (radio signal reflections)– Results vary hour by hour, day by dayResults vary hour by hour, day by day

AccuracyAccuracy

There is a substantial difference between There is a substantial difference between typical accuracy and worst-case accuracytypical accuracy and worst-case accuracyDescribed as a statistic: x% had an error of y Described as a statistic: x% had an error of y meters or lessmeters or less

Typical 95% horizontal error results for a typical day:Typical 95% horizontal error results for a typical day:

Global averageGlobal average 7.8 – 8.3 meters7.8 – 8.3 meters

Average for worst site Average for worst site (on globe)(on globe)

19.2-19.7 meters19.2-19.7 meters

Errors worse than 30 meters are possible given the potential for various atmospheric conditions and receiver faults and the possibility that satellites can be taken out of service

Accuracy andAccuracy and“Selective Availability”“Selective Availability”

Past feature of GPS SPS that purposefully Past feature of GPS SPS that purposefully degraded accuracy of position determination for degraded accuracy of position determination for non US-military usenon US-military useCivilian accuracy was typically about 100 meters Civilian accuracy was typically about 100 meters under Selective Availabilityunder Selective AvailabilitySA was discontinued May 1, 2000SA was discontinued May 1, 2000– Has not been used sinceHas not been used since– It's been replaced by “selective deniability,” which It's been replaced by “selective deniability,” which

allows the US military to geographically designate allows the US military to geographically designate areas in which to degrade GPS quality. areas in which to degrade GPS quality.

Comparing Accuracy Comparing Accuracy with and without SA – A sample with and without SA – A sample

The plots show that SA causes 95% of the points to fall within a radius of The plots show that SA causes 95% of the points to fall within a radius of 60.7 yards. Without SA, 95% of the points fall within a radius of 7.9 yards.60.7 yards. Without SA, 95% of the points fall within a radius of 7.9 yards.

Comparing Accuracy Comparing Accuracy with and without SA – Recapwith and without SA – Recap

Before, with 100 Before, with 100 meter typical meter typical accuracy allowed you accuracy allowed you to identify what to identify what stadium you were instadium you were in

Now with 6-12 meter Now with 6-12 meter typical accuracy, you typical accuracy, you can tell about which can tell about which yard line you are onyard line you are on

Accuracy – WAASAccuracy – WAAS

Wide-Area Augmentation SystemWide-Area Augmentation System– Designed specifically for aviationDesigned specifically for aviation– Commissioned by FAA in 2003Commissioned by FAA in 2003– Uses ground stations and satellitesUses ground stations and satellites

25 ground reference stations cover the entire US and parts 25 ground reference stations cover the entire US and parts of Canada and Mexicoof Canada and Mexico

– Augments GPS Standard Positioning ServiceAugments GPS Standard Positioning Service– Provides better integrity and accuracyProvides better integrity and accuracy

Typical accuracy of 3-5 meters horizontal, 3-7 meters verticalTypical accuracy of 3-5 meters horizontal, 3-7 meters vertical

– Can be used for precision approachesCan be used for precision approaches

Accuracy – WAASAccuracy – WAAS

How it works:How it works:– Two master stations, located on either coast, Two master stations, located on either coast,

collect data from the 25 reference stations collect data from the 25 reference stations and create a GPS correction message. and create a GPS correction message.

– This correction accounts for GPS satellite This correction accounts for GPS satellite orbit and clock drift plus signal delays caused orbit and clock drift plus signal delays caused by the atmosphere and ionosphere. by the atmosphere and ionosphere.

– The corrected differential message is then The corrected differential message is then broadcast through one of two geostationary broadcast through one of two geostationary satellites, and is then received by a WAAS-satellites, and is then received by a WAAS-capable GPS receiver.capable GPS receiver.

Accuracy – Differential GPSAccuracy – Differential GPS

Provides high accuracy for a small area Provides high accuracy for a small area

Uses a local ground station transmitter Uses a local ground station transmitter

Accuracy can be better than one inch Accuracy can be better than one inch

LimitationsLimitations

Requires good line-of-sight to satellitesRequires good line-of-sight to satellites– May occasionally have difficulty using GPS in May occasionally have difficulty using GPS in

vehiclesvehicles– Generally unusable inside a building (or cave)Generally unusable inside a building (or cave)

Other concernsOther concerns

GPS can be subject to accidental and intentional GPS can be subject to accidental and intentional interferenceinterference– Easily jammed using strategically placed low-power Easily jammed using strategically placed low-power

transmitterstransmitters– WAAS is also at riskWAAS is also at risk

Selective Availability (SA) or SCATANA could be Selective Availability (SA) or SCATANA could be instituted during a national emergency instituted during a national emergency (but this is unlikely)(but this is unlikely)– Current plan calls for possible use of “Selective Denial” Current plan calls for possible use of “Selective Denial”

where GPS is degraded or denied to specific where GPS is degraded or denied to specific geographic areasgeographic areas

GotchasGotchas

True vs. Magnetic directions True vs. Magnetic directions (a configuration option in some units)(a configuration option in some units)– The Apollo GX 55 will always use magnetic The Apollo GX 55 will always use magnetic

directionsdirections

Batteries!Batteries!

The need for training and practiceThe need for training and practice

Expressing coordinatesExpressing coordinates– Seconds vs. Decimal MinutesSeconds vs. Decimal Minutes

TerminologyTerminology

Describing placesDescribing places

Describing directionsDescribing directions

Terminology: WaypointTerminology: Waypoint

A specific named location either defined A specific named location either defined by the user or defined in the instrument’s by the user or defined in the instrument’s databasedatabase

Waypoints sometimes come in flavors:Waypoints sometimes come in flavors:– User defined waypointsUser defined waypoints– Built-in database waypoints (example: an Built-in database waypoints (example: an

airport)airport)

Terminology:Terminology:Defining Different DirectionsDefining Different Directions

Desired Track / CourseDesired Track / CourseBearingBearingTrackTrackHeadingHeading

** In general, you should take note whether your ** In general, you should take note whether your GPS is giving you directions as True or Magnetic GPS is giving you directions as True or Magnetic directionsdirections

** The GX-55 always gives ** The GX-55 always gives MagneticMagnetic directions directions

Describing LocationsDescribing LocationsA Choice to UnderstandA Choice to Understand

We describe latitude and longitude normally We describe latitude and longitude normally using degrees and minutesusing degrees and minutesWhen dealing with fractions of minutes there is, When dealing with fractions of minutes there is, however, a choicehowever, a choice– There are essentially two options:There are essentially two options:

1.1. One can use seconds One can use seconds (of which there are 60 in one minute)(of which there are 60 in one minute)

2.2. One can use decimal-minutes One can use decimal-minutes (i.e. tenths and hundredths of a minute)(i.e. tenths and hundredths of a minute)

– Many GPS units can be configured to display one Many GPS units can be configured to display one way or the otherway or the other

Describing LocationsDescribing LocationsYet another optionYet another option

Sometimes, latitude and longitude are Sometimes, latitude and longitude are expressed in degrees only.expressed in degrees only.

Thus the following are equivalent Thus the following are equivalent expressions of longitude:expressions of longitude:– 9393oo 20 20’’ 00 00””– 93.3333393.33333oo

Describing LocationsDescribing LocationsCAP Standard MethodCAP Standard Method

The standard we will use in CAP is The standard we will use in CAP is degrees and decimal minutesdegrees and decimal minutes– Example: Example:

45 degrees 35.4 minutes North45 degrees 35.4 minutes North93 degrees 42.2 minutes West93 degrees 42.2 minutes West

– This is the standard way the Air Force provides This is the standard way the Air Force provides coordinates to us for search and rescuecoordinates to us for search and rescue

– This is also the way our GX-55 normally displays This is also the way our GX-55 normally displays position informationposition information

In CAP we will not usually use “seconds” unless In CAP we will not usually use “seconds” unless working with another agency that wishes to do working with another agency that wishes to do so.so.

Describing Locations:Describing Locations:Communicating with OthersCommunicating with Others

The seconds vs. decimal minutes question is a big The seconds vs. decimal minutes question is a big source of confusion even within single organizationssource of confusion even within single organizations– Some people erroneously say “seconds” when they mean Some people erroneously say “seconds” when they mean

“hundredths of a minute”“hundredths of a minute”– Some people say “point” or “decimal” when they should have Some people say “point” or “decimal” when they should have

said “minutes” and “seconds”said “minutes” and “seconds”– Take nothing for granted when getting informationTake nothing for granted when getting information– Be accurate and clear when giving informationBe accurate and clear when giving information

Especially when working with other-agencies, triple-Especially when working with other-agencies, triple-check all coordinates to make sure we’re all speaking check all coordinates to make sure we’re all speaking the same languagethe same language– Some organizations normally uses Degrees-Minutes-Seconds Some organizations normally uses Degrees-Minutes-Seconds

as their standard way of describing positions, but they will use as their standard way of describing positions, but they will use the word “decimal” or “point” to separate the three parts of the the word “decimal” or “point” to separate the three parts of the coordinatecoordinate

Describing LocationsDescribing LocationsYet AnotherYet Another Approach to be Aware of Approach to be Aware of

Some GPS units also offer the option to Some GPS units also offer the option to display position information using display position information using Universal Transverse Mercator” (UTM)Universal Transverse Mercator” (UTM)– An alternative to using degrees and minutesAn alternative to using degrees and minutes– Beyond the scope of this courseBeyond the scope of this course

GX-55 Search patternsGX-55 Search patterns

Describing the patternsDescribing the patterns– Parallel Line (Grid)Parallel Line (Grid)– Creeping LineCreeping Line– Expanding SquareExpanding Square– Route and offset routeRoute and offset route

Parallel Line Search PatternParallel Line Search Patterna.k.a. “Grid Search”a.k.a. “Grid Search”

““US Grids” are areas US Grids” are areas 15 minute to a side, 15 minute to a side, serially numbered for serially numbered for each sectional chart each sectional chart (MSP means “Twin (MSP means “Twin Cities” sectional)Cities” sectional)

7.5 minute quarter 7.5 minute quarter grids are named A, B, grids are named A, B, C, and D – in C, and D – in reading reading orderorder, left to right, top , left to right, top

to bottomto bottom 94 00’ W o 93 30’ W o

45 30’ No

46 00’ No

93 45’ o

45 45’ o

414

445 446

MSP413 A

B

C D

A

Parallel Line Search PatternParallel Line Search Patterna.k.a. “Grid Search”a.k.a. “Grid Search”

The GPS unit The GPS unit labels the four labels the four corners (and also corners (and also four search four search pattern entry pattern entry points) 1, 2, 3, points) 1, 2, 3, and 4 – and 4 – clockwiseclockwise starting in starting in northwestnorthwest..

94 00’ W o 93 52.5’ W o

45 52.5’ No

46 00’ No

MSP413 A

1 2

4 3

Describing a Parallel Line PatternDescribing a Parallel Line Pattern

Grid identifier and starting waypoint Grid identifier and starting waypoint (i.e. corner of quarter-grid)(i.e. corner of quarter-grid)

Track spacingTrack spacing

Direction of tracks – either E/W or N/SDirection of tracks – either E/W or N/S

Note: Search area for a parallel line pattern in the Note: Search area for a parallel line pattern in the GX55 is always a GX55 is always a quarter-gridquarter-grid

Parallel Line Pattern ExampleParallel Line Pattern Example

Quarter Grid MSP Quarter Grid MSP 413A1413A1

• Northwest corner of Northwest corner of grid MSP 413Agrid MSP 413A

Track spacing 1 NMTrack spacing 1 NM

Tracks running east to Tracks running east to westwest

Track spacing

MSP413 A

Creeping Line Search PatternCreeping Line Search Pattern

Shaped much like a Shaped much like a parallel line pattern, but parallel line pattern, but with legs aligned with legs aligned perpendicular to a route perpendicular to a route (rather than by ordinal (rather than by ordinal directions)directions)Descriptive parts:Descriptive parts:– Starting point (any Starting point (any

waypoint)waypoint)– Direction Direction – Starting left or right sideStarting left or right side– Track spacingTrack spacing– Leg lengthLeg length– Number of legsNumber of legs

Direction

Starting on left side

Leg length

Track spacing

Starting Waypoint

Expanding SquareExpanding Square

Descriptive partsDescriptive parts– Starting waypoint (at Starting waypoint (at

center of pattern)center of pattern)– Initial directionInitial direction– Track spacingTrack spacing– Number of legsNumber of legs

Initial Direction

s2s

2s3s

s

3ss

Expanding SquareExpanding Square

Descriptive partsDescriptive parts– Starting waypoint (at Starting waypoint (at

center of pattern)center of pattern)– Initial directionInitial direction– Track spacingTrack spacing– Number of legsNumber of legs

Initial Direction

s2s

2s3s

s

3ss

Offset Track Line SearchOffset Track Line Searcha.k.a. Route Searcha.k.a. Route Search

For a returning For a returning route search, 2 route search, 2 passes are made, passes are made, each ½ track each ½ track spacing offset from spacing offset from base coursebase course

A non-returning A non-returning route search will route search will have a leg on the have a leg on the base coursebase course

TO Waypoint

FROM Waypoint

Base Course

Offset Track Line SearchOffset Track Line Searcha.k.a. Route Searcha.k.a. Route Search

For the purpose of using the GPS, we For the purpose of using the GPS, we can program only one leg at a timecan program only one leg at a time

A route leg will either be…A route leg will either be…– On the course line (in which case a simple On the course line (in which case a simple

flight plan will suffice)flight plan will suffice)– Offset from the course lineOffset from the course line

Described as a distance offset and a direction Described as a distance offset and a direction offset (either right or left of course)offset (either right or left of course)

ImprovisingImprovising

As a last resort, any GPS can display As a last resort, any GPS can display running latitude and longituderunning latitude and longitude– The crew fly the pattern watching the numbersThe crew fly the pattern watching the numbers– This can be used to guide an arbitrary grid This can be used to guide an arbitrary grid

searchsearchExample usage: we need to fly a grid which has Example usage: we need to fly a grid which has non-standard boundariesnon-standard boundaries

– This generally requires additional preflight This generally requires additional preflight preparation (to predetermine the lines of latitude preparation (to predetermine the lines of latitude and longitude)and longitude)