GPS Based Navigation Accuracy Question
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2 questions:
1. It is often NOTAM'd the GPS accuracy in NE. Italy is/maybe compromised. Why is this so?
2. Accuracy for NPA's. (nevermind PA's.) I see students fly autopilot LNAV approaches with no regard for checking the raw data lateral navigation. They should, but they don't. Now VNAV approaches are also in use it is also vital to check raw data for vertical. Again not so methodicaly done. They've checked RNP v ANP and all seems hunky dory, so they allow George to lead them to terra firma, hopefully in the correct place.
I heard that in Gulf War 1, (or was ir 2) before Bill, there was a error inputed into the civilian received GPS signal. I don't know how much. If it was deemed necessary - for national security - I presume the USA could do this again. What warning would us civvies be given about this. If the map shift was 0.5nm, and pilots blindly follow George as they do now, Ouch! Would such an inputed error trigger the message "Unable Reqd Nav Perf-RNP" during the initial approach? I assume that any such error would be acceptable at CRZ levels, but only become unsafe during terminal operations. In the CRZ would the ANP be much closer RNP value than normal thus indictaiong that there could be a problem at lower levels? (IRS + VOR/DME cross checking at lower levels would likely be within what non-GPS a/c call map shift parameters. On the B733 that was often > 0.5nm overland and often >1.0mn after seas crossings.)
Given all the NOTAM guff we have to study during the very very short flight planning phase at the start of the day I would hope there would be a very conspicuous method to alert us to any deficiencies in the system.
1. It is often NOTAM'd the GPS accuracy in NE. Italy is/maybe compromised. Why is this so?
2. Accuracy for NPA's. (nevermind PA's.) I see students fly autopilot LNAV approaches with no regard for checking the raw data lateral navigation. They should, but they don't. Now VNAV approaches are also in use it is also vital to check raw data for vertical. Again not so methodicaly done. They've checked RNP v ANP and all seems hunky dory, so they allow George to lead them to terra firma, hopefully in the correct place.
I heard that in Gulf War 1, (or was ir 2) before Bill, there was a error inputed into the civilian received GPS signal. I don't know how much. If it was deemed necessary - for national security - I presume the USA could do this again. What warning would us civvies be given about this. If the map shift was 0.5nm, and pilots blindly follow George as they do now, Ouch! Would such an inputed error trigger the message "Unable Reqd Nav Perf-RNP" during the initial approach? I assume that any such error would be acceptable at CRZ levels, but only become unsafe during terminal operations. In the CRZ would the ANP be much closer RNP value than normal thus indictaiong that there could be a problem at lower levels? (IRS + VOR/DME cross checking at lower levels would likely be within what non-GPS a/c call map shift parameters. On the B733 that was often > 0.5nm overland and often >1.0mn after seas crossings.)
Given all the NOTAM guff we have to study during the very very short flight planning phase at the start of the day I would hope there would be a very conspicuous method to alert us to any deficiencies in the system.
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Given all the NOTAM guff we have to study during the very very short flight planning phase at the start of the day I would hope there would be a very conspicuous method to alert us to any deficiencies in the system.
Perhaps if some European carriers had a reasonable dispatch department in place (Monarch and Lufthansa are especially good in this department, in my experience) all this shuffling through NOTAMS would then be done by the dispatch staff, and called to the attention of the pilots.
You get what you pay for.
Some slight misunderstandings, I fear?
The US GPS system sends C/A and P code signals. C/A ('coarse acquisition) is the 'civilian' version and used to include Selective Availability (SA) before Clinton ordered it to be switched off. SA applied random time error signals and vehicle ephemeris values to reduce system accuracy to levels which would not pose a serious threat if misused by terrorists.
But with Differential GPS improving C/A accuracy, SA became rather unnecessary. WAAS will improve C/A accuracy even further in the USA and EGNOS will do the same (one of these days
) in €uroland. Most modern Garmin systems include WAAS/EGNOS compatability.
Military systems use far more accurate P-code ('precision') signals which use faster digital code sequences. Originally it was thought that the P-code position information would be 10 x as accurate as C/A; however, C/A was so accurate that SA was needed to degrade it when necessary.
It would be possible for a civilian user to use some clever processing to use P-code signals by detecting the C/A 'handover word', accessing the L1 and L2 frequencies and using the P-codes. So the P-code is also encrypyted; it is then know as Y-code. Unless cryptovariables are loaded into a mil spec GPS receiver, it will only use C/A positioning.
The US GPS system sends C/A and P code signals. C/A ('coarse acquisition) is the 'civilian' version and used to include Selective Availability (SA) before Clinton ordered it to be switched off. SA applied random time error signals and vehicle ephemeris values to reduce system accuracy to levels which would not pose a serious threat if misused by terrorists.
But with Differential GPS improving C/A accuracy, SA became rather unnecessary. WAAS will improve C/A accuracy even further in the USA and EGNOS will do the same (one of these days
) in €uroland. Most modern Garmin systems include WAAS/EGNOS compatability.Military systems use far more accurate P-code ('precision') signals which use faster digital code sequences. Originally it was thought that the P-code position information would be 10 x as accurate as C/A; however, C/A was so accurate that SA was needed to degrade it when necessary.
It would be possible for a civilian user to use some clever processing to use P-code signals by detecting the C/A 'handover word', accessing the L1 and L2 frequencies and using the P-codes. So the P-code is also encrypyted; it is then know as Y-code. Unless cryptovariables are loaded into a mil spec GPS receiver, it will only use C/A positioning.
Some more info:
KGPS is the "location" needed to find GPS NOTAMS. Or go to the US Coast Guard site, which for some reason, is the source of those NANU (GPS for NOTAM) Notice Announcements for Navstar Users.
The US Mil cannot use Y-code for navigation in civil airspace, our GPS navigation was certified for C/A signals only. There have been one or two huge screw-ups (read: domestic GNEs using bombing computers as nav devices in US civil airspace
)
When they started bombing with GPS navigation, errors were found by targeteers where bombs aimed for the top of the building (think elevator shaft) instead hit near the first floor. Hence targeting had to get smart on how to program for elevation. Also, a mid-90s Space Shuttle mission, I believe classified, spent 12 days mapping the earth for elevations which, in turn, produced the obstacle and terrain data used by Enhanced GPWS.
The detritus of the years
GF
KGPS is the "location" needed to find GPS NOTAMS. Or go to the US Coast Guard site, which for some reason, is the source of those NANU (GPS for NOTAM) Notice Announcements for Navstar Users.
The US Mil cannot use Y-code for navigation in civil airspace, our GPS navigation was certified for C/A signals only. There have been one or two huge screw-ups (read: domestic GNEs using bombing computers as nav devices in US civil airspace
)When they started bombing with GPS navigation, errors were found by targeteers where bombs aimed for the top of the building (think elevator shaft) instead hit near the first floor. Hence targeting had to get smart on how to program for elevation. Also, a mid-90s Space Shuttle mission, I believe classified, spent 12 days mapping the earth for elevations which, in turn, produced the obstacle and terrain data used by Enhanced GPWS.
The detritus of the years
GF
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RAT 5 Questions
- The problems with GPS in Italy used to be interference from television signals. I thought that had been sorted out now but I will watch the Notams.
- The RNP value associated with a nav fit has an accuracy, integrity, continuity and availabilityrequirement. The GPS element of that nav fit has a receiver with additional channels which are used for monitoring the integrity of the signals. This is known as GPS Receiver Autonomous Integrity Monitoring (RAIM). Any jamming or selective availability imposed on the GPS would be detected as an increase in the dilution of precision (the cocked hat gets bigger) and a RAIM failure. ICAO specifications for RNP receivers require pilot alerting of inadequate navigation performance whenever actual performance is worse than RNP.
A good review of FMS integrated navigation can be found at http://adsb.tc.faa.gov/WG4_Meetings/ASAS10%202005-July/STP%20appendix%20B_08-05-2005%20AWW.pdf
Cheers Chart8R
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Or go to the US Coast Guard site, which for some reason....
The USCG maintains the very first navigation equipment (transmitters) used for area navigation...LORAN.
Loran C now...Loran A, many years ago.
Very accurate, if used properly....and with Loran A, it took a definite technique, ofter mastered only by the professional Navigator.
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Accuracy is only one performance item to be respected by a navigation system. I write NAVIGATION system. GPS is by all means just a POSITIONING system. Only thru software programs using databases one can make a Navigation system out of the GPS. However, the other three factors are availabitliy, reliability and integrity. On the last parameter, i.e. integrity, GPS fails in more than one respect to be a precision system. (think of these databases being filled by humans!).
Nevertheless, for en-route purposes it´s a hell of a system. I love it too. Especially in my CAR!!
But to be a true precision NAV sytem, one has to consider definitely other system like MLS. But off course...as the yanks didn´t invent it, they don´t adopt it.
Nevertheless, for en-route purposes it´s a hell of a system. I love it too. Especially in my CAR!!
But to be a true precision NAV sytem, one has to consider definitely other system like MLS. But off course...as the yanks didn´t invent it, they don´t adopt it.
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Greetings'
quote:
However, the other three factors are availabitliy, reliability
and integrity. On the last parameter, i.e. integrity, GPS fails in more than one respect to be a precision system.
Availability, Continuity, and Integrity are criteria that if demonstrated at 95% of the time will grant a sole mean of navigation certification status to the system.
Now as integrity is a stake for the GPS, then it cannot be certified as sole mean but as PRIMARY mean of navigation, PRECISION has nothing to do with this
Furthermore as per TSO129C a self embarked software, within the receiver, has to have the capabitility to verify the integrity, in our case it is called RAIM, Receiver Autonomous Integrity Monitoring
quote:
However, the other three factors are availabitliy, reliability
and integrity. On the last parameter, i.e. integrity, GPS fails in more than one respect to be a precision system.Availability, Continuity, and Integrity are criteria that if demonstrated at 95% of the time will grant a sole mean of navigation certification status to the system.
Now as integrity is a stake for the GPS, then it cannot be certified as sole mean but as PRIMARY mean of navigation, PRECISION has nothing to do with this
Furthermore as per TSO129C a self embarked software, within the receiver, has to have the capabitility to verify the integrity, in our case it is called RAIM, Receiver Autonomous Integrity Monitoring
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Dunno, we fly GBAS approaches in Europe to CAT I limit with the availability of CAT III once certified. It is very precise indeed, no difference to ILS from a users standpoint. However that is ground augmented so of course you can get more precise position data than with pure GPS.
Sadly, those approaches are still flagged as being in a trial phase, however they work wonderfully so far and we had no glitches whatsoever.
Sadly, those approaches are still flagged as being in a trial phase, however they work wonderfully so far and we had no glitches whatsoever.
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Please: Has anyone got an answer to the questions asked? Pilots should not play like politicians and answer the question they thought was asked.
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Greetings,
what was the question
On the Airbus there is a page called PREDICTIVE GPS, it will show RAIM availabilty at a specific waypoint (destination for example) at a specific time (ETA)
On B777 the GPS receiver will compute a data relevant to RAIM availability and sends it to AIMS.
So I guess that if you are on Boeing world on top of the NOTAMS specific to GPS you need to have RAIM holes.
Because you cannot shoot an approach using GPS as main sensors if RAIM is not available.
RAIM needs 5 sats (if you are baro aided) 7.5 deg above the horizon.
Now North of Italy is mountaineous? may be mountain shaddowing is reducing the number of sat you can receive.
what was the question
On the Airbus there is a page called PREDICTIVE GPS, it will show RAIM availabilty at a specific waypoint (destination for example) at a specific time (ETA)
On B777 the GPS receiver will compute a data relevant to RAIM availability and sends it to AIMS.
So I guess that if you are on Boeing world on top of the NOTAMS specific to GPS you need to have RAIM holes.
Because you cannot shoot an approach using GPS as main sensors if RAIM is not available.
RAIM needs 5 sats (if you are baro aided) 7.5 deg above the horizon.
Now North of Italy is mountaineous? may be mountain shaddowing is reducing the number of sat you can receive.
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What was the question
RAW DATA MONITORING was mandatory at time aircraft were equipped with a single FMS, to enable the crew to continue the approach on Raw Data in case of FMS failure
if you are equipped with dual FMS with GPS, then you dont need to cross check the raw data as long as ANP<RNP.
But before all this the Approaches MUST BE VALIDATED, and the validation depends on the type on NPA you want to fly, is it Classic NPA overlay, is it RNAV, is it RNP, is it GPS.
What was the question
RAW DATA MONITORING was mandatory at time aircraft were equipped with a single FMS, to enable the crew to continue the approach on Raw Data in case of FMS failure
if you are equipped with dual FMS with GPS, then you dont need to cross check the raw data as long as ANP<RNP.
But before all this the Approaches MUST BE VALIDATED, and the validation depends on the type on NPA you want to fly, is it Classic NPA overlay, is it RNAV, is it RNP, is it GPS.
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Now as integrity is a stake for the GPS, then it cannot be certified as sole mean but as PRIMARY mean of navigation.
WAAS certified GPS navigators can (and are being) installed in aircraft as a sole means of navigation, and are fully certified as such.
Don't need VOR.
Don't need ADF.
Don't need DME/TACAN.
WAAS/GPS only, if you so desire.
Of course, others trail behind, which is no surprise...
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GPS (excluding waas laas dgps) is primary means of navigation, my statement was on GPS only
However, lets look at the enroute case.
L1011 aircraft equipped with dual Honeywell HT-9100 or Universal UNS-1M GPS navigators.
Fully approved for MNPS north Atlantic ops as a sole means of enroute navigation...and this was over ten years ago.
I suspect that other aircraft/equipment combinations were as well.
Dual Omega equipped aircraft, is another example.
Now, having said this, usually these aircraft were also equipped with INS units, but not always...and not specifically required by the ops specs issued to the specific carrier.
Now, a few will say...never.
Oddly enough, there usually are exceptions, fully approved by the relevant regulatory authorities.
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Greetings
as far as I know, the IRS, (Omega before it was decommissioned) is the only Sole mean of navigation, even for enroute consideration GPS still primary means, LITTON recently attempted to certify the AIME solution (Autonumous Integrity Monitoring Extrapolation) using Kalman filtering, but I am not sure if they did get it.
We have to remember that the Integrity is the GPS weak point, and therefore it cannot be certified sole mean, the last attempt I know of was the Rio de Janiero ICAO meeting in 1998, integrity and jamming closed the subject.
as far as I know, the IRS, (Omega before it was decommissioned) is the only Sole mean of navigation, even for enroute consideration GPS still primary means, LITTON recently attempted to certify the AIME solution (Autonumous Integrity Monitoring Extrapolation) using Kalman filtering, but I am not sure if they did get it.
We have to remember that the Integrity is the GPS weak point, and therefore it cannot be certified sole mean, the last attempt I know of was the Rio de Janiero ICAO meeting in 1998, integrity and jamming closed the subject.
Last edited by kijangnim; 3rd Aug 2008 at 18:00. Reason: adding missing omega
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We have to remember that the Integrity is the GPS weak point, and therefore it cannot be certified sole mean....
I suspect our UK/European friends just simply don't like the GPS idea, due to the 'not invented here' syndrome.
And yet...they will use one to find the nearest Italian restaurant in a strange town where they have never been before...
Go figure.
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Greetings 411A
Personally i am not European, and living in France doesnot make you French either, so I dont have any bias about who made what.
I want to point out that during the Rio de Janiero ICAO conference the Sole mean of navigation GPS certificate was dropped because of JAMMING, it was never dropped because of other integrity issues since RAIM handles it very nicely
Personally i am not European, and living in France doesnot make you French either, so I dont have any bias about who made what
.I want to point out that during the Rio de Janiero ICAO conference the Sole mean of navigation GPS certificate was dropped because of JAMMING, it was never dropped because of other integrity issues since RAIM handles it very nicely
- Somebody we have no control over can turn it off.
- It's only one system, and fallible like any human endeavour
- It is very easy to jam.
But, GPS approaches are coming in Europe and the UK, they're approved now in the UK for some GA, - and once Galileo is fully available, a combined GPS/Galileo receiver will solve at least two of those three problems, and make the third harder to do.
G