RAIM

[idisaid]

RAIM outage predicted for NPA as flw
- what is exact meaning of this
-why RAIM expected at this time of day for NPA not DEPARTURE SID?
RAIM is only apply to NPA?

[VinRouge]

All to do with RNP vs RNAV performanced based requirements.

NPA = RNP requirement (containment) for example, RNP0.3, or RNP 0.15(AR)
SID typically RNAV1

Comes down to definitions.

Required Navigation Performance (RNP) Specification. Area navigation specification that includes the performance control and alerting requirement, designated by the prefix RNP; e.g., RNP 4, RNP APCH, RNP AR APCH.

Area Navigation (RNAV) Specification.- Area navigation specification that does not include the performance control and alerting requirement, designated by the prefix RNAV; e.g., RNAV 5, RNAV 2, RNAV 1.



Also, depends on your certification standard:

5) If only TSO-C129 equipment is used to meet RNAV 1 and RNAV 2 requirements, it is necessary to confirm RAIM availability for the flight route (route and time) foreseen, using current GNSS satellite information.
6) If only TSO-C145/C146 equipment is used to meet RNAV requirements, the pilot/operator does not need to make any prediction if it is confirmed that the wide area augmentation system (WAAS) coverage is available along the entire flight route.

Taken from:

https://www.icao.int/SAM/eDocuments/5PBN%20AC%2091-003%20RNAV1-RNAV2%20eng.pdf

[CaptainProp]

why RAIM expected at this time of day for NPA not DEPARTURE SID?

Because RAIM (predictive) is used to assess signal availability along a route in the coming hours. In other words, can I plan to fly this route and approach at the times I’m expecting to cross and area / arrive at a specific airport. If you’re on ground and there is no signal availability you have the option to use non gps based departure or cancel flight.

CP

[VinRouge]

Some technical standards require GPS lock prior to commencing the takeoff run. It depends upon the aircraft. I believe the INS Lat/Long on the 73 are confirmed at the threshold by engaging TOGA (not my type so dont shoot me down pls...)

[Fursty Ferret]

Pragmatically speaking, you need two things to fly GPS approaches to LPV minimums... GPS (obviously) and the ability to detect if that signal is degraded or inaccurate.
​​​​​​
That's where RAIM comes in. It doesn't make the approach any more accurate, but it does allow you to check the validity of your calculated position.

You can calculate a good fix from six or nine SVs, but you need 24(23?) for RAIM to work. You can calculate in advance whether you'll have that many, which is why you have a note to that effect.

Honeywell FMS on the Airbus can do the calculation for you. I've never seen it come up with a negative answer, but you'd expect good coverage at middle latitudes in the northern hemisphere.

[underfire]

With many RNP procedures, especially RNP-AR, part of the preflight is the RAIM Prediction Report. If dispatch or crew determines there is not sufficient GPS coverage, the procedure cannot be used. Currently your typical RAIM report is NPA (arrival and alternate airports), and route. If the SID is RNAV, a RAIM check is required.

AUGUR RAIM Prediction (http://augur.eurocontrol.int/ec/terminal-approach)
https://sapt.faa.gov/raim-summaries.php?outageType=129001450

Many of the mountainous routes in China, the only procedures are RNP AR, so the RAIM check is imperative for both RNP AR departure and RNP AR approach.

Here is what you need for RAIM, minimum of 5 sats for fault detection, 6 sats for fault detection and exclusion. The HPL is also a consideration.
The FMS is always calculating RAIM, and enroute always governs over prediction, so this can have quite the effect on the flight.

[underfire]

Example Current Prediction http://www.nstb.tc.faa.gov/24Hr_WaasRNP3.htm
https://cimg6.ibsrv.net/gimg/www.gmforum.com-vbulletin/1350x750/raim_rnp1_78eb6e0217a57236cbe1c5da08cecb3f92e7fe15.png

[wiedehopf]

[....]
Here is what you need for RAIM, minimum of 5 sats for fault detection, 6 sats for fault detection and exclusion. The HPL is also a consideration.
The FMS is always calculating RAIM, and enroute always governs over prediction, so this can have quite the effect on the flight.

Out of curiosity what is the influence of WAAS or similar systems on this?

[underfire]

With WAAS, you do not need a RAIM check for LNAV/VNAV approach, LPV approach. AFAIK, you still have to RAIM check for RNAV RNP. The HPL/VPL need to be checked.
RAIM checks are no longer required unless you lose WAAS coverage. With WAAS, the receiver can now be used for primary navigation. But these receivers, certified under TSO C146, must still check for integrity of your GPS position solution, and this check is more sophisticated since there are new integrity requirements for approaches with vertical guidance that are more stringent than for LNAV approaches.