Validity of RAIM Prediction ION ITM 2011 San Diego, CA Jan. 24-26, 2011 Takeyasu Sakai Electronic Navigation Research Institute, Japan Takeyasu Sakai Electronic

Validity of RAIM PredictionValidity of RAIM Prediction

ION ITM 2011ION ITM 2011San Diego, CASan Diego, CA

Jan. 24-26, 2011Jan. 24-26, 2011

Takeyasu SakaiElectronic Navigation Research Institute, Japan

Takeyasu SakaiElectronic Navigation Research Institute, Japan

ION ITM Jan. 2011ION ITM Jan. 2011 - Slide - Slide 22

IntroductionIntroduction• Background of RAIM:Background of RAIM:

– GNSS is an essential tool for implementation of PBN;GNSS is an essential tool for implementation of PBN;

– GPS needs to be augmented in terms of integrity for aviation applications; GPS needs to be augmented in terms of integrity for aviation applications; GPS itself does not provide enough integrity as GNSS;GPS itself does not provide enough integrity as GNSS;

– The ICAO (international civil aviation organization) GNSS standard defines The ICAO (international civil aviation organization) GNSS standard defines several augmentation systems: SBAS, GBAS, and ABAS;several augmentation systems: SBAS, GBAS, and ABAS;

– RAIM (receiver autonomous integrity monitoring) is a kind of ABAS which is a RAIM (receiver autonomous integrity monitoring) is a kind of ABAS which is a mechanism that the receiver ensures a certain level of integrity;mechanism that the receiver ensures a certain level of integrity;

– FAA TSO-C129 and RTCA DO-208 require RAIM function.FAA TSO-C129 and RTCA DO-208 require RAIM function.

• Use of GPS/RAIM (GPS augmented by RAIM):Use of GPS/RAIM (GPS augmented by RAIM):– In many countries, GPS/RAIM is usable for IFR flights;In many countries, GPS/RAIM is usable for IFR flights;

– Mostly RAIM prediction is required before flight to check the availability of Mostly RAIM prediction is required before flight to check the availability of GPS/RAIM for the intended operation;GPS/RAIM for the intended operation;

– Recently Japan Civil Aviation Bureau (JCAB) ordered an investigation on how Recently Japan Civil Aviation Bureau (JCAB) ordered an investigation on how reliable RAIM prediction is; This presentation is summary of the investigation.reliable RAIM prediction is; This presentation is summary of the investigation.


Augmentation SystemsAugmentation Systems

SBASSBASSatellite-Based Augmentation SystemSatellite-Based Augmentation SystemGPS-compatible signal from GEOGPS-compatible signal from GEO

ABASABASAircraft-Based Augmentation SystemAircraft-Based Augmentation System

RAIM, Baro aidingRAIM, Baro aiding

GBASGBASGround-Based Augmentation SystemGround-Based Augmentation System

VHF signal from the groundVHF signal from the ground

MSASMSAS

• GNSS: GPS + augmentation system (SBAS, GBAS, or ABAS);GNSS: GPS + augmentation system (SBAS, GBAS, or ABAS);• RAIM (receiver autonomous integrity monitoring): a mechanism of ABAS;RAIM (receiver autonomous integrity monitoring): a mechanism of ABAS;• TSO-C129 certified receiver must implement RAIM function.TSO-C129 certified receiver must implement RAIM function.

GPS must be augmentedGPS must be augmentedin terms of integrityin terms of integrity

GPS constellationGPS constellation


Fundamental of RAIMFundamental of RAIM

Measures range

Measures range

between GPS and receiver

between GPS and receiver

Detects failure of satelliteDetects failure of satelliteby range anomalyby range anomaly

• Requires 5 or more GPS satellites;Requires 5 or more GPS satellites;• The receiver warns pilot (or FMS) when it detects failure of GPS satellite;The receiver warns pilot (or FMS) when it detects failure of GPS satellite;• RAIM FD: Detects failure and outputs warning;RAIM FD: Detects failure and outputs warning;• RAIM FDE: Detects failure and exclude the anomalous satellite, then continues RAIM FDE: Detects failure and exclude the anomalous satellite, then continues

operation (For FDE, requires 6 or more satellites).operation (For FDE, requires 6 or more satellites).


Part 1Part 1

Background and MotivationBackground and Motivation


Current Situation in JapanCurrent Situation in Japan• Regulation:Regulation:

– In Japan, use of GPS/RAIM is currently limited to supplemental navigation In Japan, use of GPS/RAIM is currently limited to supplemental navigation because availability of GPS/RAIM is not enough;because availability of GPS/RAIM is not enough;

– Supplemental navigation system: Aircraft must equip other primary navigation Supplemental navigation system: Aircraft must equip other primary navigation system and the route is planned based on the primary navigation system;system and the route is planned based on the primary navigation system;

– Many small business planes equip TSO-C129 GPS receivers but they cannot Many small business planes equip TSO-C129 GPS receivers but they cannot fly RNAV route directly going to the destination by GPS/RAIM only;fly RNAV route directly going to the destination by GPS/RAIM only;

– Additionally, RAIM prediction is mandatory; If GPS/RAIM is predicted Additionally, RAIM prediction is mandatory; If GPS/RAIM is predicted unavailable for the intended operation, they should change the flight plan.unavailable for the intended operation, they should change the flight plan.

• Recent situation:Recent situation:– Business operators have strongly requested JCAB to allow using GPS/RAIM Business operators have strongly requested JCAB to allow using GPS/RAIM

as a primary navigation source which enables to fly RNAV route without as a primary navigation source which enables to fly RNAV route without additional equipment;additional equipment;

– JCAB is now considering to relax the regulation and allow GPS/RAIM as a JCAB is now considering to relax the regulation and allow GPS/RAIM as a primary navigation source.primary navigation source.


Supplemental Navigation SourceSupplemental Navigation Source

Supplemental NavigationSupplemental Navigation

• Equipage:Equipage:– Aircraft must equip other primary navigation Aircraft must equip other primary navigation

system;system;– The route is planned based on the primary The route is planned based on the primary

navigation system.navigation system.

• Operation:Operation:– Pilots must monitor primary navigation source to Pilots must monitor primary navigation source to

check correctness of supplemental navigation;check correctness of supplemental navigation;– If pilots find any doubt in supplemental navigation, If pilots find any doubt in supplemental navigation,

they must change navigation source to the they must change navigation source to the primary;primary;

– RAIM prediction is mandatory.RAIM prediction is mandatory.

• Benefit:Benefit:– The route is limited by the coverage of primary The route is limited by the coverage of primary

navigation system;navigation system;– Cannot fly RNAV route by GPS/RAIM only.Cannot fly RNAV route by GPS/RAIM only.

PrimaryPrimaryNavigationNavigation

SupplementalSupplementalNavigationNavigation


Primary Navigation SourcePrimary Navigation Source

Primary NavigationPrimary Navigation

• Equipage:Equipage:– Aircraft must equip other backup navigation Aircraft must equip other backup navigation

system to fly the alternate route;system to fly the alternate route;– For approach, the backup navigation system must For approach, the backup navigation system must

be available at the alternate airport;be available at the alternate airport;– The route is planned based on the primary The route is planned based on the primary

navigation system.navigation system.

• Operation:Operation:– RAIM prediction is mandatory; If predicted RAIM prediction is mandatory; If predicted

unavailable, they should change the flight plan;unavailable, they should change the flight plan;– In case that the primary navigation source fails, In case that the primary navigation source fails,

pilots change navigation source to the backup and pilots change navigation source to the backup and fly the alternate route (airport). fly the alternate route (airport).

• Benefit:Benefit:– Possible to plan the route based on the primary Possible to plan the route based on the primary

navigation source; Enabling RNAV by GPS/RAIM.navigation source; Enabling RNAV by GPS/RAIM.

BackupBackupNavigationNavigation

PrimaryPrimaryNavigationNavigation

Alternate RouteAlternate RoutePlannedPlannedRouteRoute


Sole Mean NavigationSole Mean Navigation

Sole Mean NavigationSole Mean Navigation

• Equipage:Equipage:– Aircraft do not need to equip any other navigation Aircraft do not need to equip any other navigation

system;system;– RAIM FD cannot serve as a sole mean navigation; RAIM FD cannot serve as a sole mean navigation;

At least RAIM FDE is necessary because At least RAIM FDE is necessary because continuous operation against failure of GPS continuous operation against failure of GPS satellite is necessary.satellite is necessary.

• Operation:Operation:– RNP operation with enough integrity of navigation;RNP operation with enough integrity of navigation;– RAIM prediction is still required. RAIM prediction is still required.

• Benefit:Benefit:– Small planes with less equipage can fly to remote Small planes with less equipage can fly to remote

islands.islands.

Sole MeanSole MeanNavigationNavigation


RAIM PredictionRAIM Prediction

Is GPS approach Is GPS approach possible on the possible on the

planned arrival time?planned arrival time?

Is GPS/RAIM available Is GPS/RAIM available along with the planned along with the planned

route?route?

DestinationDestinationAirportAirport

OriginOriginAirportAirport

• RAIM prediction: It is required to check availability of GPS/RAIMRAIM prediction: It is required to check availability of GPS/RAIM

for the intended operation before flight;for the intended operation before flight;• Because GPS/RAIM does not have enough availability and often unavailable;Because GPS/RAIM does not have enough availability and often unavailable;• If GPS/RAIM is predicted to be unavailable, flight plan should be changed;If GPS/RAIM is predicted to be unavailable, flight plan should be changed;• In Japan, ATM Center performs RAIM prediction everyday for Enroute, Terminal, In Japan, ATM Center performs RAIM prediction everyday for Enroute, Terminal,

and Approach, respectively, and issues NOTAM for unavailable operations.and Approach, respectively, and issues NOTAM for unavailable operations.


Expected InvestigationExpected Investigation• Possible problem: Missed Alarm EventPossible problem: Missed Alarm Event

– There might be ‘Missed Alarm Event’ that RAIM prediction says ‘GPS will be There might be ‘Missed Alarm Event’ that RAIM prediction says ‘GPS will be available’ but actually GPS/RAIM is not available; Then the pilot uses backup available’ but actually GPS/RAIM is not available; Then the pilot uses backup navigation system or changes the destination to the alternative airport;navigation system or changes the destination to the alternative airport;

– Relaxing the regulation to allow use of GPS/RAIM as a primary navigation source, Relaxing the regulation to allow use of GPS/RAIM as a primary navigation source, ATC controllers have a concern and wish to know how often such an event ATC controllers have a concern and wish to know how often such an event occurs and how wide the affected region is;occurs and how wide the affected region is;

– JCAB decided to observe the situation by a two-year-trial with limited users and to JCAB decided to observe the situation by a two-year-trial with limited users and to conduct an investigation to estimate the effects.conduct an investigation to estimate the effects.

• Investigation ordered by JCAB:Investigation ordered by JCAB:– Problem is due to unscheduled outage (failure) of GPS satellite;Problem is due to unscheduled outage (failure) of GPS satellite;

– Reliability of GPS satellites: the number of satellites, availability, and failure rate;Reliability of GPS satellites: the number of satellites, availability, and failure rate;

– Lists unscheduled outage of GPS satellite;Lists unscheduled outage of GPS satellite;

– Detailed investigation of ‘Missed Alarm Event’ that RAIM prediction said OK but Detailed investigation of ‘Missed Alarm Event’ that RAIM prediction said OK but actually GPS/RAIM was unavailable: Illustrates affected region and temporal actually GPS/RAIM was unavailable: Illustrates affected region and temporal range.range.


Concern of ATC ControllersConcern of ATC Controllers

GPS fails,GPS fails,change routechange route

Sudden outageSudden outagedue to failuredue to failure

Wow !!!Wow !!!

• ‘‘Missed Alarm Event’:Missed Alarm Event’: RAIM prediction says RAIM prediction says ‘GPS will be available’ but actually GPS ‘GPS will be available’ but actually GPS becomes unavailable;becomes unavailable;

• Many aircraft flying by GPS/RAIM suddenly Many aircraft flying by GPS/RAIM suddenly lose primary navigation simultaneously;lose primary navigation simultaneously;

• How much does it affect to ATC operation?How much does it affect to ATC operation?



GPS fails,GPS fails,change routechange routeATC ControllersATC Controllers


Part 2Part 2

Summary of InvestigationSummary of Investigation


GPS Satellite FailuresGPS Satellite FailuresEvent Occurred NANU ID NANU Issued SVN Repaired Case #

07/08/24 17:51 2007102 07/08/24 17:55 40 07/09/18 20:28 <1>

07/09/15 12:50 2007106 07/09/15 13:07 53 07/09/15 16:13 <2>

07/10/08 04:37 2007118 07/10/08 04:39 59 07/10/08 16:36 <3>

07/10/08 06:33 2007119 07/10/08 06:37 58 07/10/08 16:49 <4>

07/10/08 21:04 2007123 07/10/08 21:34 41 07/10/09 01:43 <5>

07/10/09 08:55 2007125 07/10/09 08:56 60 07/10/09 11:16 <6>

07/10/10 08:24 2007129 07/10/10 08:28 51 07/10/10 11:04 <7>

08/03/25 02:30 2008034 08/03/25 02:36 40 08/03/27 23:49 <8>

08/04/02 09:46 2008037 08/04/02 12:27 58 08/04/02 15:08 <9>

08/04/26 02:46 2008044 08/04/26 03:13 61 08/04/29 12:14 <10>

08/08/05 23:38 2008084 08/08/05 23:49 35 08/10/07 20:49 <11>

09/07/25 01:28 2009046 09/07/25 02:24 54 09/07/26 16:00 <12>

• There were 30 cases of sudden failure of GPS satellite for years 2007 to 2009;There were 30 cases of sudden failure of GPS satellite for years 2007 to 2009;• Among them, 12 cases listed here affected RAIM prediction in Japan;Among them, 12 cases listed here affected RAIM prediction in Japan;• 5 cases on 07/10/08 to 07/10/10 are due to trouble in the GPS MCS; There were 8 5 cases on 07/10/08 to 07/10/10 are due to trouble in the GPS MCS; There were 8

independent cases for 3 years; Frequency of the Event: 8 / 3 = independent cases for 3 years; Frequency of the Event: 8 / 3 = 2.667 events/year2.667 events/year..

MCSMCSTroubleTrouble


Investigation of Each CaseInvestigation of Each Case• Detailed investigation of each case:Detailed investigation of each case:

– Comparison between output of RAIM prediction and actual receiver behavior for Comparison between output of RAIM prediction and actual receiver behavior for each case of GPS satellite failure;each case of GPS satellite failure;

– Illustrates affected region and temporal range of ‘Missed Alarm Event’.Illustrates affected region and temporal range of ‘Missed Alarm Event’.

• ATM Center RAIM prediction system:ATM Center RAIM prediction system:– Assumes GPS/RAIM receivers meet TSO-C129 requirements (Classic RAIM);Assumes GPS/RAIM receivers meet TSO-C129 requirements (Classic RAIM);– Computes ARP (approximate radial-error protected) index and compares with Computes ARP (approximate radial-error protected) index and compares with

the threshold predefined for each phase of flight; ARP is rough estimation of the the threshold predefined for each phase of flight; ARP is rough estimation of the largest horizontal position error similar with HPL (horizontal protection level);largest horizontal position error similar with HPL (horizontal protection level);

– If ARP exceeds the threshold, GPS/RAIM is unavailable for the associate If ARP exceeds the threshold, GPS/RAIM is unavailable for the associate operation.operation.

Phase of FlightEnroute

(RNAV5)

Terminal

(RNAV1)Non Precision

Approach

Maximum ARP Allowed

2262 m 1135 m 352 m

Threshold of ARP index for each phase of flightThreshold of ARP index for each phase of flight


AssumptionsAssumptions• Estimation of RAIM prediction behavior:Estimation of RAIM prediction behavior:

– Implemented ARP computation algorithm and parameters same as RAIM Implemented ARP computation algorithm and parameters same as RAIM prediction system in the ATM Center;prediction system in the ATM Center;

– Assume RAIM prediction is performed on 21:00 local time (12:00 UTC) everyday Assume RAIM prediction is performed on 21:00 local time (12:00 UTC) everyday based on ‘FORECAST’ NANU info. (scheduled maintenance of GPS satellites);based on ‘FORECAST’ NANU info. (scheduled maintenance of GPS satellites);

– GPS satellite position: computed with archive of almanac information; Mask GPS satellite position: computed with archive of almanac information; Mask angle is 7.5 degrees;angle is 7.5 degrees;

– NOTAM is issued if GPS/RAIM is unavailable for 5 minutes or more;NOTAM is issued if GPS/RAIM is unavailable for 5 minutes or more;

– The estimation result is compared with the operational NOTAM (Available since The estimation result is compared with the operational NOTAM (Available since 9/27/2007); They completely matched.9/27/2007); They completely matched.

• Estimation of GPS/RAIM receiver behavior:Estimation of GPS/RAIM receiver behavior:– Assumes onboard GPS/RAIM receivers determine if GPS/RAIM is available or Assumes onboard GPS/RAIM receivers determine if GPS/RAIM is available or

not by the computation identical with ATM Center;not by the computation identical with ATM Center;

– Computes ARP index based on ‘ACTUAL’ NANU information (failure and Computes ARP index based on ‘ACTUAL’ NANU information (failure and maintenance report of GPS satellites) and compares with the threshold.maintenance report of GPS satellites) and compares with the threshold.


Case <1>: Temporal VariationCase <1>: Temporal Variation

Case <1> 07/08/24 17:51 SVN40Case <1> 07/08/24 17:51 SVN40

• Computed ARP variation for each case;Computed ARP variation for each case;• Target location is Osaka Int’l Airport; At the center of Japan and GPS approach is Target location is Osaka Int’l Airport; At the center of Japan and GPS approach is

available there;available there;• Case <1>: ARP increased at the same time as SVN40 failure, but less than threshold.Case <1>: ARP increased at the same time as SVN40 failure, but less than threshold.

Threshold forThreshold forApproach (352m)Approach (352m)

Threshold forThreshold forTerminal (1135m)Terminal (1135m)

Threshold forThreshold forEnroute (2262m)Enroute (2262m)

ARP by RAIM ARP by RAIM predictionprediction

Actual ARPActual ARPDifferenceDifference

Actual >Actual > PredictionPrediction

SatelliteSatelliteFailureFailure


Cases <2> to <4>Cases <2> to <4>

Case <3> 07/10/08 04:37 SVN59Case <3> 07/10/08 04:37 SVN59Case <4> 07/10/08 06:33 SVN58Case <4> 07/10/08 06:33 SVN58

Case <2> 07/09/15 12:50 SVN53Case <2> 07/09/15 12:50 SVN53

• Cases <2> and <4>: RAIM prediction said GPS/RAIM is unavailable only for Approach; Cases <2> and <4>: RAIM prediction said GPS/RAIM is unavailable only for Approach; Actually it became unavailable for Enroute and Terminal, and for Approach for longer thActually it became unavailable for Enroute and Terminal, and for Approach for longer than the prediction;an the prediction;

• Case <2>: No NOTAM because it was not operated yet;Case <2>: No NOTAM because it was not operated yet;


Cases <5> and <6>Cases <5> and <6>


• Case <5>: ARP increased at the same time as SVN41 failure; GPS Approach became Case <5>: ARP increased at the same time as SVN41 failure; GPS Approach became unavailable later at 21:38 and continued unavailable for 31 minutes until 22:09;unavailable later at 21:38 and continued unavailable for 31 minutes until 22:09;

• RAIM prediction could not work and NOTAM was not issued for Case <5>;RAIM prediction could not work and NOTAM was not issued for Case <5>;• Case <6>: RAIM prediction said GPS Approach is unavailable; Actually it became unavCase <6>: RAIM prediction said GPS Approach is unavailable; Actually it became unav

ailable for Enroute and Terminal, and for Approach for longer than the prediction.ailable for Enroute and Terminal, and for Approach for longer than the prediction.




• Case <7>: RAIM prediction said GPS Approach is unavailable; Actually it became unavCase <7>: RAIM prediction said GPS Approach is unavailable; Actually it became unavailable for Enroute and Terminal, and for Approach for longer than the prediction;ailable for Enroute and Terminal, and for Approach for longer than the prediction;

• Case <8>: ARP increased due to failure and GPS/RAIM could not be used for ApproacCase <8>: ARP increased due to failure and GPS/RAIM could not be used for Approach; RAIM prediction could not work and NOTAM was not issued.h; RAIM prediction could not work and NOTAM was not issued.




• Case <9>: ARP increased due to failure, but less than threshold;Case <9>: ARP increased due to failure, but less than threshold;• Case <10>: ARP increased due to failure and GPS/RAIM could not be used for Case <10>: ARP increased due to failure and GPS/RAIM could not be used for

Approach; RAIM prediction could not work and NOTAM was not issued.Approach; RAIM prediction could not work and NOTAM was not issued.




• Case <11>: NOTAM was issued by RAIM prediction but actually GPS/RAIM was available;Case <11>: NOTAM was issued by RAIM prediction but actually GPS/RAIM was available;• Regular RAIM prediction does not predict the effect on 04:30 UTC, but extra prediction was Regular RAIM prediction does not predict the effect on 04:30 UTC, but extra prediction was

performed as response to NANU reporting failure of SVN35 and the extra NOTAM was issued;performed as response to NANU reporting failure of SVN35 and the extra NOTAM was issued;• Case <12>: ARP increased due to failure and GPS/RAIM could not be used for Approach; Case <12>: ARP increased due to failure and GPS/RAIM could not be used for Approach;

RAIM prediction could not work and NOTAM was not issued.RAIM prediction could not work and NOTAM was not issued.

False AlarmFalse Alarm


Spatial ImpactSpatial Impact• Observes affected region for some cases that RAIM prediction could not Observes affected region for some cases that RAIM prediction could not

work properly:work properly:– For consideration of effects on ATC operation;For consideration of effects on ATC operation;

– ‘‘Missed Alarm Event’: RAIM prediction said OK but actually unavailable;Missed Alarm Event’: RAIM prediction said OK but actually unavailable;

– Illustrated as colored plots on a map as follows:Illustrated as colored plots on a map as follows:

RAIM prediction says GPA/RAIM is available and actually it is available (No RAIM prediction says GPA/RAIM is available and actually it is available (No Alarm); There is no RAIM NOTAM and GPS/RAIM is available normally.Alarm); There is no RAIM NOTAM and GPS/RAIM is available normally.

RAIM prediction says GPS/RAIM is unavailable but actually it is available (False RAIM prediction says GPS/RAIM is unavailable but actually it is available (False Alarm); RAIM NOTAM is issued and GPS/RAIM is not used for operation; There Alarm); RAIM NOTAM is issued and GPS/RAIM is not used for operation; There is no safety problem but availability of GPS/RAIM navigation is lowered. is no safety problem but availability of GPS/RAIM navigation is lowered.

RAIM prediction says GPS/RAIM is unavailable and actually it is unavailable RAIM prediction says GPS/RAIM is unavailable and actually it is unavailable (True Alarm); RAIM NOTAM is issued and GPS/RAIM is not used for operation; (True Alarm); RAIM NOTAM is issued and GPS/RAIM is not used for operation; This case means RAIM prediction works properly.This case means RAIM prediction works properly.

RAIM prediction says GPS/RAIM is available but actually it is unavailable RAIM prediction says GPS/RAIM is available but actually it is unavailable (Missed Alarm); RAIM prediction fails to issue NOTAM reporting GPS/RAIM is (Missed Alarm); RAIM prediction fails to issue NOTAM reporting GPS/RAIM is unavailable; GPS/RAIM suddenly becomes unavailable during operation.unavailable; GPS/RAIM suddenly becomes unavailable during operation.

Predict: AvailablePredict: AvailableActual: AvailableActual: Available

Predict: UnavailablePredict: UnavailableActual: AvailableActual: Available

Predict: UnavailablePredict: UnavailableActual: UnavailableActual: Unavailable

Predict: AvailablePredict: AvailableActual: UnavailableActual: Unavailable


Case <2> EnrouteCase <2> Enroute

• Computed for Case <2> for Enroute operation; Case <2> looks affected widely;Computed for Case <2> for Enroute operation; Case <2> looks affected widely;• Interval: 10 minutes per frame;Interval: 10 minutes per frame;• No effect immediately after the failure; The region where GPS/RAIM is unavailablNo effect immediately after the failure; The region where GPS/RAIM is unavailabl

e without NOTAM appears 110 minutes after the failure.e without NOTAM appears 110 minutes after the failure.





Interval: 10 minInterval: 10 min


Case <2> Enroute: 130 minCase <2> Enroute: 130 min

• Case <2>: 130 minutes after the failure of SVN 53;Case <2>: 130 minutes after the failure of SVN 53;• The region where GPS/RAIM is unavailable without NOTAM grew up to a half The region where GPS/RAIM is unavailable without NOTAM grew up to a half

size of Japan.size of Japan.





Snapshot:Snapshot:130 min after failure130 min after failure


Case <2> TerminalCase <2> Terminal

• Computed for Case <2> for terminal operation;Computed for Case <2> for terminal operation;• No effect immediately after the failure; The region where GPS/RAIM is No effect immediately after the failure; The region where GPS/RAIM is

unavailable without NOTAM appears 30 minutes after the failure and disappears;unavailable without NOTAM appears 30 minutes after the failure and disappears;• The red region appears again 100 minutes after and covers whole of Japan.The red region appears again 100 minutes after and covers whole of Japan.







Case <2> Terminal: 110 minCase <2> Terminal: 110 min

• Case <2>: 110 minutes after the failure of SVN 53;Case <2>: 110 minutes after the failure of SVN 53;• The red region covers whole of Japan; Terminal area operation is affected The red region covers whole of Japan; Terminal area operation is affected

nationwide;nationwide;• Such a situation continued for 40 minutes.Such a situation continued for 40 minutes.







Case <2> ApproachCase <2> Approach

• Computed for Case <2> for non precision approach operation;Computed for Case <2> for non precision approach operation;• Prediction and actual are identical immediately after the failure;Prediction and actual are identical immediately after the failure;• The region where GPS/RAIM is unavailable without NOTAM appears 20 minutes The region where GPS/RAIM is unavailable without NOTAM appears 20 minutes

after the failure and disappears;after the failure and disappears;• The red region appears again 80 minutes after and covers whole of Japan.The red region appears again 80 minutes after and covers whole of Japan.







Case <2> Approach: 110 minCase <2> Approach: 110 min

• Case <2>: 110 minutes after the failure of SVN 53;Case <2>: 110 minutes after the failure of SVN 53;• The red region covers whole of Japan; Non precision approach is suddenly The red region covers whole of Japan; Non precision approach is suddenly

stopped nationwide;stopped nationwide;• Such a situation continued for 120 minutes.Such a situation continued for 120 minutes.







Case <12> Approach: 10 minCase <12> Approach: 10 minPredict: AvailablePredict: AvailableActual: AvailableActual: Available




• Case <12>; 10 minutes after the failure of SVN 54;Case <12>; 10 minutes after the failure of SVN 54;• The red region covers whole of Japan; Non precision approach is suddenly The red region covers whole of Japan; Non precision approach is suddenly

stopped nationwide; Such a situation continued for 30 minutes;stopped nationwide; Such a situation continued for 30 minutes;• There is a case that the red region appears only 10 minutes after the failure.There is a case that the red region appears only 10 minutes after the failure.



ConclusionConclusion• Current Situation in Japan:Current Situation in Japan:

– Use of GPS/RAIM is currently limited to supplemental navigation;Use of GPS/RAIM is currently limited to supplemental navigation;

– JCAB is now considering to relax the regulation and allow GPS/RAIM as a JCAB is now considering to relax the regulation and allow GPS/RAIM as a primary navigation source.primary navigation source.

• Concerns and Investigation Ordered by JCAB:Concerns and Investigation Ordered by JCAB:– ATC controllers have a concern on ‘Missed Alarm Event’;ATC controllers have a concern on ‘Missed Alarm Event’;

– JCAB decided to observe the situation by a two-year-trial with limited users and JCAB decided to observe the situation by a two-year-trial with limited users and to conduct an investigation to estimate the effects.to conduct an investigation to estimate the effects.

• Investigation of each failure case:Investigation of each failure case:– There were 8 cases RAIM prediction affected by GPS satellite failure in Japan There were 8 cases RAIM prediction affected by GPS satellite failure in Japan

for years 2007 to 2009; 2.667 events/year;for years 2007 to 2009; 2.667 events/year;

– It was confirmed that GPS satellite failure could make GPS/RAIM navigation It was confirmed that GPS satellite failure could make GPS/RAIM navigation unavailable without prediction; Affected region and temporal range is not small;unavailable without prediction; Affected region and temporal range is not small;

– In fact, there are cases that GPS/RAIM navigation is lost for Terminal and In fact, there are cases that GPS/RAIM navigation is lost for Terminal and Approach phases of flight over the whole of Japan.Approach phases of flight over the whole of Japan.


BackupBackup

Statistics on the Number ofStatistics on the Number ofAvailable GPS SatellitesAvailable GPS Satellites


Source: NANU InformationSource: NANU Information• NANU (Notice Advisory to Navstar Users) information:NANU (Notice Advisory to Navstar Users) information:

– Information on GPS satellites issued by GPS operator;Information on GPS satellites issued by GPS operator;– Provides information on launch, decommission, maintenance, and failure of each GPS satellite;Provides information on launch, decommission, maintenance, and failure of each GPS satellite;– Distributed by E-mail; Archive is also available.Distributed by E-mail; Archive is also available.

• Scheduled maintenance information:Scheduled maintenance information:– NANU notifies scheduled maintenanceNANU notifies scheduled maintenance

by a few days before;by a few days before;– After the maintenance, actual down periodAfter the maintenance, actual down period

is reported;is reported;– RAIM prediction is performed based onRAIM prediction is performed based on

this ‘FORECAST’ information.this ‘FORECAST’ information.

• Failure information:Failure information:– GPS satellite failure is quickly reported whenGPS satellite failure is quickly reported when

the event is detected: Latency is a fewthe event is detected: Latency is a fewminutes to a few hours (Not guaranteed:minutes to a few hours (Not guaranteed:sometimes missed to report);sometimes missed to report);

– After repair, actual down period is reported;After repair, actual down period is reported;– Actual availability of GPS/RAIM is estimatedActual availability of GPS/RAIM is estimated

based on this ‘ACTUAL’ information.based on this ‘ACTUAL’ information.

NOTICE ADVISORY TO NAVSTAR USERS (NANU) 2009003NOTICE ADVISORY TO NAVSTAR USERS (NANU) 2009003SUBJ: SVN59 (PRN19) FORECAST OUTAGE JDAY 042/2230 - JDAY 043/1230SUBJ: SVN59 (PRN19) FORECAST OUTAGE JDAY 042/2230 - JDAY 043/12301. NANU TYPE: FCSTDV1. NANU TYPE: FCSTDV NANU NUMBER: 2009003NANU NUMBER: 2009003 NANU DTG: 061721Z FEB 2009NANU DTG: 061721Z FEB 2009 REFERENCE NANU: N/AREFERENCE NANU: N/A REF NANU DTG: N/AREF NANU DTG: N/A SVN: 59SVN: 59 PRN: 19PRN: 19 START JDAY: 042START JDAY: 042 START TIME ZULU: 2230START TIME ZULU: 2230 START CALENDAR DATE: 11 FEB 2009START CALENDAR DATE: 11 FEB 2009 STOP JDAY: 043STOP JDAY: 043 STOP TIME ZULU: 1230STOP TIME ZULU: 1230 STOP CALENDAR DATE: 12 FEB 2009STOP CALENDAR DATE: 12 FEB 2009

2. CONDITION: GPS SATELLITE SVN59 (PRN19) WILL BE UNUSABLE ON 2. CONDITION: GPS SATELLITE SVN59 (PRN19) WILL BE UNUSABLE ON JDAY 042JDAY 042 (11 FEB 2009) BEGINNING 2230 ZULU UNTIL JDAY 043 (12 FEB 2009)(11 FEB 2009) BEGINNING 2230 ZULU UNTIL JDAY 043 (12 FEB 2009) ENDING 1230 ZULU.ENDING 1230 ZULU.

NANU Sample (NANU 2009003)NANU Sample (NANU 2009003)

Scheduled MaintenanceScheduled Maintenance

Start Date/TimeStart Date/Time

Stop Date/TimeStop Date/Time


Available GPS SatellitesAvailable GPS Satellites

# of Satellites in Operation# of Satellites in Operation Excluding Outage PeriodExcluding Outage Period

• Statistics on the number of available GPS satellites for years 2007 to 2009;Statistics on the number of available GPS satellites for years 2007 to 2009;• 29 to 31 satellites are operated; 29 satellites for 8% of the whole period;29 to 31 satellites are operated; 29 satellites for 8% of the whole period;• Considering outages due to maintenance and failure shows there is 27 Considering outages due to maintenance and failure shows there is 27

satellites period for 0.04% (10 hours), and 29 or more for 95%.satellites period for 0.04% (10 hours), and 29 or more for 95%.


Available GPS SatellitesAvailable GPS Satellites

GPS Satellites in OperationGPS Satellites in Operation

Excluded Maintenance and Excluded Maintenance and FailureFailure

• Statistics on the number of Statistics on the number of available GPS satellites for years available GPS satellites for years 2007 to 2009;2007 to 2009;

• 29 to 31 satellites are operated;29 to 31 satellites are operated;• Up to 3 satellites are down Up to 3 satellites are down due due

to maintenance and/or failure.to maintenance and/or failure.


Availability and Failure RateAvailability and Failure RateAverage of all satellites MTBF [h] MTTR [h] Availability

All Outage 4739.0 53.77 0.988781

Only Maintenance 5816.5 24.51 0.995805

Only Failure 22072.8 181.55 0.991842

• Computes MTBO (mean time between outage) and MTTR (mean time to Computes MTBO (mean time between outage) and MTTR (mean time to repair) based on NANU information;repair) based on NANU information;

• Availability of the system:Availability of the system:

• Estimation of frequency that a GPS satellite in view fails suddenly: Assuming Estimation of frequency that a GPS satellite in view fails suddenly: Assuming failure rate of 1 / 22072.8 per hour per satellite, mean number of visible failure rate of 1 / 22072.8 per hour per satellite, mean number of visible satellites as 7:satellites as 7:

7 / 22072.8 7 / 22072.8 * * 24 24 * * 365 = 365 = 2.778 events/year.2.778 events/year.

Documents

Validity of RAIM Prediction ION ITM 2011 San Diego, CA Jan. 24-26, 2011 Takeyasu Sakai Electronic Navigation Research Institute, Japan Takeyasu Sakai Electronic