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RMC
4th Mar 2019, 14:45
last week we did a transatlantic flight with the short runway at Halifax being the only one available inside crosswind limits . It has a GPS only approach and RAIM predicted a short outage during our planned diversion window. We elected to use it as we had enough fuel to hold if the outage actually translated to a loss of ANP. I believe Canadian airports are not SBAS and so my question is.....if the outage were significantly longer would we have to plan for a different ERA . Can be tricky as our ETOPS range is being reduced due engine issues. Thanks in advance.

Skyjob
5th Mar 2019, 09:29
You may need to consider that, or think like you did already in operational terms, what is the likelihood of you arriving at the diversion alternate while the RAIM is out, worst case scenario and you arrive at the onset of the outage, ensure you have additional fuel to remain there to see it through

RMC
5th Mar 2019, 18:59
Thanks Skyjob. We have only had satellite outage info since we got complex PBN approval (RNP-AR APPROACHES) .The other thing that isn't clear from the new brief material is how some RNP requirements may have outages and some don't presumably if only RNP 1 is out and all other RNP ranges have no outage we can use any approach which does not have an RNP 1 requirement.

Skyjob
5th Mar 2019, 20:37
Different airlines use different tools, here is one that can be used by anyone AUGUR RAIM Prediction (http://augur.eurocontrol.int/ec/terminal-approach)
Ensure your selection matches the requirements for your aircraft type and flight, run the report and use it.

Airlines may only provide you with best capability, ANP AR would require this detailed information to be made available.
If outage occur, you can always run a lower criteria requirement if an approach allows you to use it, the minima will likely then be different and planning may need to take this into account

RMC
7th Mar 2019, 19:49
Good point...so in the ETOPS ERA case would have to apply ETOPS planning minima on top of the increased minima.

Smythe
8th Mar 2019, 00:29
Couple of blended issues here. GPS only approach or RNP-AR only approach?

RAIM prediction is run before you depart, and if there is an outage predicted, you cannot plan to use that approach. As it is a prediction, there are the RAIM calcs real time on the aircraft. That is what really matters.

RAIM needs a minimum of 6 satellites to provide the fault detection and exclusion.

With RNP-AR, you are required to have the RAIM provide the acceptable HIL/HPL for the applicable RNP level. You may still have GPS coverage sufficient for an RNAV GPS approach, but RNP -AR is different.

Enroute, you need to real-time monitor HIL/HPA to ensure that you meet the required RNP level for the procedure at arrival.

The HIL coefficient is a circle around the ac keeping it with the 2x RNP boundaries. It is not the 2x boundary, but an alarm to tell you that you are getting close. If it exceeds the required level, you will get the Horizontal Alarm Limit (HAL) on the procedure and are required to discontinue the procedure.

As noted in your example, the RAIM enroute may allow for an RNP 0.5 vs 0.3 RNP, but I have not really seen a procedure where there are multiple RNP levels with associated minima. I am not sure what you mean by increased minima by RNP level, or am I misreading this? Just so you know, if the procedure is designed for 0.1 it is 0.1, you cannot use it at 0.3 RNP

The northern latitudes are very well covered, so I see little issue on coverage, nor the prediction viability.

Different airlines use different tools, here is one that can be used by anyone AUGUR RAIM Prediction (http://augur.eurocontrol.int/ec/terminal-approach)

This is a Eurocontrol program. For flight ops in in North America use this http://www.nstb.tc.faa.gov/24Hr_RAIM.htm note 0.1 and 0.3 HAL coverage.
The HAL of 0.3RNP is 556m but depending on the FMC, it will alarm before this, as in reality HIL and HAL or not the same.