RAIM Check
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RAIM Check
What's the gen on checking for RAIM using the aircraft's equipment .. is it mandatory even if one gets timely Notam advice about possible outages for specific locations?
If there's a mandatory requirement to get RAIM prediction onboard (in flight or pre-departure) even though one has a clear Notam in the hand, where is this stipulation to be found?
From what i've read, Notam advice regarding RAIM availability is possibly a superior source of the info' than what the onboard machine might say(?!).
If there's a mandatory requirement to get RAIM prediction onboard (in flight or pre-departure) even though one has a clear Notam in the hand, where is this stipulation to be found?
From what i've read, Notam advice regarding RAIM availability is possibly a superior source of the info' than what the onboard machine might say(?!).
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My understanding is that the RAIM check within the GPS uses it's onboard almanac to predict if a suitable number of satellites will be available at the time and place specified, whereas the NAIPS RAIM check incorporates other real time information such as satellite health and serviceability to provide a RAIM prediction.
At least for C129a GPS it's mandatory to check RAIM prior to an instrument approach. It is an almanac look up process.
The C146a GPS units have fault detection, so they may automatically warn of loss of RAIM. But, I have C129a, so I'm not sure.
It's rare not to have RAIM, but it does happen. GPS can be jammed also.
The C146a GPS units have fault detection, so they may automatically warn of loss of RAIM. But, I have C129a, so I'm not sure.
It's rare not to have RAIM, but it does happen. GPS can be jammed also.
At least for C129a GPS it's mandatory to check RAIM prior to an instrument approach. It is an almanac look up process.
The C146a GPS units have fault detection, so they may automatically warn of loss of RAIM. But, I have C129a, so I'm not sure.
The C146a GPS units have fault detection, so they may automatically warn of loss of RAIM. But, I have C129a, so I'm not sure.
A RAIM prediction from Airways is more up to date/accurate than one done in the aircraft.
TSO C129 units will give a RAIM warning.
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TSO C129 and 145/146 certified receivers must have an automatic RAIM prediction service prior to passing the FAF.
They must not enter Approach mode if the prediction fails, or if in any event RAIM is not available at the FAF.
If a receiver doesn't do those things without pilot input, it's not suitable for IFR use.
This information is found in the FAA's TSO archive.
As wishiwasupthere says, a paper NOTAM prediction is superior.
Apparently there are some ATOs who mandate a manual RAIM prediction in flight. It's good airmanship to know how to do this, but in most cases there is no legal requirement to do so.
They must not enter Approach mode if the prediction fails, or if in any event RAIM is not available at the FAF.
If a receiver doesn't do those things without pilot input, it's not suitable for IFR use.
This information is found in the FAA's TSO archive.
As wishiwasupthere says, a paper NOTAM prediction is superior.
Apparently there are some ATOs who mandate a manual RAIM prediction in flight. It's good airmanship to know how to do this, but in most cases there is no legal requirement to do so.
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throwing a spanner in the works
From the NAIPS GPS RAIM Australia page:
"The Airservices Australia Receiver Autonomous Integrity Monitoring (RAIM) Prediction Service (RPS) provides predictions of RAIM availability for flight planning purposes only.
Pilots-in-command are reminded that the predictions are based on information received from the GPS Operating Authority.
In flight, pilots-in-command should use the RAIM prediction facility of their GPS equipment for RAIM availability predictions.
Presence of RAIM should be continuously monitored whenever GPS is used for navigation."
"The Airservices Australia Receiver Autonomous Integrity Monitoring (RAIM) Prediction Service (RPS) provides predictions of RAIM availability for flight planning purposes only.
Pilots-in-command are reminded that the predictions are based on information received from the GPS Operating Authority.
In flight, pilots-in-command should use the RAIM prediction facility of their GPS equipment for RAIM availability predictions.
Presence of RAIM should be continuously monitored whenever GPS is used for navigation."
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As wishiwasupthere says, a paper NOTAM prediction is superior
So even if there isn't a legal requirement for it, I think "It's good airmanship" should apply.
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Hmm. It seems there is a lack of traction on the issue of automatic versus manual RAIM events.
2bigmelons,
All pilots use the RAIM prediction facility of their TSO'd receiver. It's automatic, prior to all GPS approaches.
And indeed it is; continuous and automatic, for any TSO'd GPS receiver in NAV mode.
The issue is, will the pilot notice the little flashing light or little blinking message that tells you RAIM isn't or won't be available. That's what needs monitoring, and that is at the heart of the NAIPS & CASA advice.
iPahlot,
You are right, of course. But here is the problem: if you do a manual prediction 30mins before ETA, I can ask you to do another one at 29mins. Or 28, or 27. At any stage, a hitherto unpredicted fault might develop. Where does it end? The law requires a prediction before flight (NOTAM) and a prediction before the approach begins (automatic). Where do the extra checks end? How can you justify a manual check at time T, but not at time T+1?
I mentioned good airmanship. Here's when I might do a manual prediction:
Proceeding to destination, then having to divert to a destination,
a) for which I will need a GPS approach and
b) for which I don't have a NOTAM prediction and
c) knowing I will have limited fuel on arrival for go arounds and holding.
That I think would require a manual receiver prediction as soon as possible.
Regards all,
O8
2bigmelons,
In flight, pilots-in-command should use the RAIM prediction facility of their GPS equipment for RAIM availability predictions.
Presence of RAIM should be continuously monitored whenever GPS is used for navigation.
The issue is, will the pilot notice the little flashing light or little blinking message that tells you RAIM isn't or won't be available. That's what needs monitoring, and that is at the heart of the NAIPS & CASA advice.
iPahlot,
I don't think the RAIM prediction is that smart that it will look in to the future and predict that a satellite will develop a fault while you are enroute.
I mentioned good airmanship. Here's when I might do a manual prediction:
Proceeding to destination, then having to divert to a destination,
a) for which I will need a GPS approach and
b) for which I don't have a NOTAM prediction and
c) knowing I will have limited fuel on arrival for go arounds and holding.
That I think would require a manual receiver prediction as soon as possible.
Regards all,
O8
Last edited by Oktas8; 20th May 2014 at 23:45. Reason: Speeling chek
I don't think the RAIM prediction is that smart that it will look in to the future and predict that a satellite will develop a fault while you are enroute.
So even if there isn't a legal requirement for it, I think "It's good airmanship" should apply.
So even if there isn't a legal requirement for it, I think "It's good airmanship" should apply.
From memory the almanac in the box is downloaded once a week, at least on the type I fly.
While the RAIM prediction data from Airservices might be a couple of hours old, the data on your GPS/FMS is more likely several days old.
A RAIM prediction is totally different to a warning or failure.
Last edited by glekichi; 21st May 2014 at 00:09. Reason: fixed quote
The receiver will not sequence onto appch (or LNAV) mode if RAIM won't be available, so the idea of doing the manual check is so that you can select a different approach before you even begin, rather than waiting until it's about to transition and being unable to continue.
The argument about NAIPS' prediction being more accurate is correct, but irrelevant as it is the GNSS unit's own database (as Glekichi has pointed out) that will determine if the unit sequences onwards, not NAIPS.
The argument about NAIPS' prediction being more accurate is correct, but irrelevant as it is the GNSS unit's own database (as Glekichi has pointed out) that will determine if the unit sequences onwards, not NAIPS.
The argument about NAIPS' prediction being more accurate is correct, but irrelevant as it is the GNSS unit's own database (as Glekichi has pointed out) that will determine if the unit sequences onwards, not NAIPS.
I understand the NAIPS FD/FDE prediction is more accurate as it can have info on scheduled outages/maintenance which the units almanac will/may not have.
The receiver will not sequence onto appch (or LNAV) mode if RAIM won't be available, so the idea of doing the manual check is so that you can select a different approach before you even begin, rather than waiting until it's about to transition and being unable to continue.
From memory the almanac in the box is downloaded once a week, at least on the type I fly.
MakeitHappenCaptain:
The argument about NAIPS' prediction being more accurate is correct, but irrelevant as it is the GNSS unit's own database (as Glekichi has pointed out) that will determine if the unit sequences onwards, not NAIPS.
The argument about NAIPS' prediction being more accurate is correct, but irrelevant as it is the GNSS unit's own database (as Glekichi has pointed out) that will determine if the unit sequences onwards, not NAIPS.
Whether or not the unit scales to approach mode/approach active has nothing to do with whats in the almanac. If the GPS has the required satellite coverage for RAIM, it will scale, if it doesn't it won't scale, simple as that. It doesn't matter what the almanac says.
I've seen units fail to go to approach mode/approach active even though RAIM was available. Poor satellite geometry relative to the ships GPS aerial might cause this.
All the almanac does, is provide data to predict if RAIM will be available. Nothing more nothing less.
Baldeangel:
The receiver will not sequence onto appch (or LNAV) mode if RAIM won't be available, so the idea of doing the manual check is so that you can select a different approach before you even begin, rather than waiting until it's about to transition and being unable to continue.
The receiver will not sequence onto appch (or LNAV) mode if RAIM won't be available, so the idea of doing the manual check is so that you can select a different approach before you even begin, rather than waiting until it's about to transition and being unable to continue.
If the GPS has the required satellite coverage for RAIM, it will scale, if it doesn't it won't scale, simple as that. It doesn't matter what the almanac says.
I thought it would use the almanac?
I've seen units fail to go to approach mode/approach active even though RAIM was available. Poor satellite geometry relative to the ships GPS aerial might cause this.
Why would you bother if you had the RAIM prediction from ASA or Airways. The RAIM prediction from the ships GPS unit isn't going to tell you anything that you don't know. As has been already said the ASA or Airways prediction is going to be more accurate anyway.
So the problem arises when a satellite is scheduled to be offline for whatever reason, but the status is changed to be online, and this happens between the retrieval of NOTAMS and the almanac getting to the aircraft (once again, pretty sure from training material this happens once a week only on the particular Universal FMS I use).
Airservices updates their information to correctly reflect this, NOTAMS say all ok, but the box doesn't know, so refuses to go into approach mode because it thinks it won't have RAIM but in fact it will. Thats assuming the satellite that it thinks is offline will make the number available less than that required for RAIM.
VERY rare scenario, but I guess you could say it is a reason to do the RAIM prediction in flight.
As for the flight test / instrument renewal form item - check RAIM availability - is there a RAIM warning or failure flag? If not then you have RAIM and checking for the absence of a flag IS checking its availability.
Airservices updates their information to correctly reflect this, NOTAMS say all ok, but the box doesn't know, so refuses to go into approach mode because it thinks it won't have RAIM but in fact it will. Thats assuming the satellite that it thinks is offline will make the number available less than that required for RAIM.
VERY rare scenario, but I guess you could say it is a reason to do the RAIM prediction in flight.
As for the flight test / instrument renewal form item - check RAIM availability - is there a RAIM warning or failure flag? If not then you have RAIM and checking for the absence of a flag IS checking its availability.
Last edited by glekichi; 21st May 2014 at 09:10. Reason: clarification
Having a read of the Universal user manual for the unit I use interestingly says:
During enroute and approach operations, the FMS provides pilot- requested predictions of RAIM availability at the selected ARRIVE waypoint for a period of ETA ±15 minutes in five minute increments.
NOTE: The FMS does not provide automatic RAIM prediction at approach arming and activation.
Hense why it would be prudent to conduct one in flight prior to approach.
During enroute and approach operations, the FMS provides pilot- requested predictions of RAIM availability at the selected ARRIVE waypoint for a period of ETA ±15 minutes in five minute increments.
NOTE: The FMS does not provide automatic RAIM prediction at approach arming and activation.
Hense why it would be prudent to conduct one in flight prior to approach.
If its got the new software that doesn't do the old prediction and lock out the approach if it doesn't predict RAIM, why do one?
Are you going to not shoot the approach if it says no RAIM but the more up to date NOTAM says you will have RAIM?
Are you going to not shoot the approach if it says no RAIM but the more up to date NOTAM says you will have RAIM?
How does the receiver predict RAIM will be available for 5 minutes after passing the FAF without knowing where the satellites will be in the constellation?
I thought it would use the almanac?
I thought it would use the almanac?
My understanding is RAIM warnings are inhibited after the FAF and the GPS will provide a DR nav solution for 5 minutes after the loss of RAIM after passing the FAF, meaning an approach can be completed and if necessary missed approach can be carried out in DR mode.
How do you know RAIM was available at the time?
I still don't see any point in doing a RAIM prediction just prior to the approach so long as you have one from ASA or Airways. You are not going to learn anything that you don't already know.
Remember we are talking about a prediction based on an almanac, what happens in real life can be and is different.
While there may be enough satellites to ensure RAIM there can be other factors that will cause a GPS unit to not have RAIM available.
Not sure if the units have the new or old software, I know its 1000 series software and are 146 units. Have done approaches in day VMC without the
in-flight RAIM prediction, and there was no lock-out of APPR mode.
No I wouldn't.
in-flight RAIM prediction, and there was no lock-out of APPR mode.
Are you going to not shoot the approach if it says no RAIM but the more up to date NOTAM says you will have RAIM?
AFAIK older universal systems locked you out of approach mode if the internal almanac said you weren't going to have RAIM at the ETA, based on an automatic RAIM prediction when an approach was armed. Later revisions removed this restriction because it was outdated and from a time when the more accurate/up to date database was not readily available..... I could be totally wrong on that, but it is my understanding.
So, an out of date RAIM prediction says no, a more current one says yes, and there has not been a RAIM failure or warning, but you're going to turn around and go home if thats the only approach?
Why?
You've still got enough satellites to navigate and to tell if one of those is giving erroneous information - if you didn't you'd have a warning.
Are you going to not shoot the approach if it says no RAIM but the more up to date NOTAM says you will have RAIM?
No I wouldn't.
No I wouldn't.
Why?
You've still got enough satellites to navigate and to tell if one of those is giving erroneous information - if you didn't you'd have a warning.
So, an out of date RAIM prediction says no, a more current one says yes, and there has not been a RAIM failure or warning, but you're going to turn around and go home if thats the only approach?
Why?
Why?
Company SOP's. Regs say RAIM must be available prior to descending below LSAT/MSA.
Its a bit like not tuning and testing a ground navaid just because it is not NOTAM'd as being unserviceable.