GPS RAIM predictions

[Biggles_in_Oz]

Does anyone actually use the GPS RAIM info which is included in a TAF ?

I thought that TSO-certified GPS's could calculate the RAIM holes, so what is the point in having a human-readable version ?

Printing 2 or 3 ARFORs' now consumes around 30 pages :( and I'm getting the irrits with 55-line TAFs that contain only about 5 lines of actual weather info.

Here's a recent example.

COOTAMUNDRA (YCTM)

RAIM GPS RAIM PREDICTION 051401
YCTM
TSO-C129 (AND EQUIVALENT)
FAULT DETECTION
09051401 TIL 09051407
09051653 TIL 09051659
09061348 TIL 09061403
09061649 TIL 09061655
09071344 TIL 09071358
09071645 TIL 09071651
09081340 TIL 09081354
GPS RAIM FD UNAVBL FOR NPA
TSO-C146A (AND EQUIVALENT)
FAULT DETECTION
NO GPS RAIM FD OUTAGES FOR NPA
FAULT DETECTION AND EXCLUSION
09051653 TIL 09051706
09052018 TIL 09052024
09052034 TIL 09052039
09052312 TIL 09052326
09060009 TIL 09060037
09060124 TIL 09060134
09060219 TIL 09060227
09060237 TIL 09060314
09060335 TIL 09060346
09060637 TIL 09060723
09061649 TIL 09061702
09062014 TIL 09062020
09062030 TIL 09062035
09062308 TIL 09062322
09070005 TIL 09070033
09070120 TIL 09070130
09070215 TIL 09070223
09070233 TIL 09070310
09070331 TIL 09070342
09070633 TIL 09070718
09071645 TIL 09071658
09072010 TIL 09072016
09072026 TIL 09072031
09072304 TIL 09072318
09080001 TIL 09080029
09080116 TIL 09080126
09080211 TIL 09080219
09080228 TIL 09080306
09080327 TIL 09080338
09080629 TIL 09080714
GPS RAIM FDE UNAVBL FOR NPA

TAF TAF YCTM 051848Z 2008 05008KT 9999 LIGHT RAIN FEW030 BKN120 FM22
05008KT 9999 LIGHT RAIN SCT020 BKN080 FM05 05008KT 8000 LIGHT RAIN
BKN010 BKN070 INTER 2303 4000 RAIN BKN012 TEMPO 0308 4000 RAIN
BKN010 T 06 09 10 10 Q 1016 1016 1014 1012

[ContactMeNow]

The only times I have used the RAIM prediction was when I was doing my ME-CIR exam to show that I wasnt going to have RAIM on any of my approaches....

I also had the RAIM prediction print out from NAIPS as well..., but the ATO was alot happier with me using the GPS functions, just as I was taxiing out...

[27/09]

I thought that TSO-certified GPS's could calculate the RAIM holes, so what is the point in having a human-readable version ?


I stand to be corrected but as far as I know the GPS relies on almanac data to make a RAIM prediction. This does not allow for a Space Vehicle (satellite) that has been taken out of service for some reason.

The most accurate RAIM prediction comes from a source that has access to information provided by the US Department of Defence. They promulgate NANU's (Notice Advisories to Navstar Users).

Also the human readable version is quite handy when you are planning the flight, so that you know RAIM will be available at you ETA before you even light the fires.

[Biggles_in_Oz]

from http://www.asy.faa.gov/safety_products/GPSSafetyAdv.htm
RAIM for Integrity
... The GPS technical standard order (TSO) requires all IFR-approved receivers to have RAIM. A RAIM algorithm works by overdetermining position using at least five satellites or four satellites and a baro altitude input from an encoding altimeter or altitude encoder. The receiver will sound a RAIM alarm (an annunciator light) if one or more satellites are providing questionable data.
The RAIM alarm limit for en route operations is 30 seconds; for nonprecision approaches, it's 10 seconds, meaning the receiver must be capable of detecting an integrity fault in that amount of time. For future GPS precision approaches, the RAIM alarm limit will be six seconds. If a RAIM alarm is active, the receiver will continue to navigate in en route mode, but it will not operate in approach mode until the RAIM limitation is resolved. RAIM will be the primary means of assuring integrity until the wide area augmentation system (WAAS) is fully operational.

27/09
Also the human readable version is quite handy when you are planning the flight, so that you know RAIM will be available at you ETA before you even light the fires.
I can see that that would be usefull, but as I don't need to do approaches in crappy weather, I would prefer to have much slimmer ARFOR/TAF/NOTAM printouts.
Perhaps the NAIPS briefings could have another user-selected option to generate a seperate GPS RAIM briefing ? ala the MET/NOTAM/Head Office NOTAM options on the NAIPS software.

[Captain Starlight]

Biggles

The RAIM forecast enables you to plan the flight and interpret operational requirements just as you do with a TAF for the destination.

In flight, a RAIM check of the receiver, invoked by you, provides an updated assurance that all is ok for your ETA at destination.

It's a bit like tuning, identing and testing a navaid, which you already do anyway.

As for the forest of trees consumed in printing the forecast, there are a couple of things you can do to save the forests.

Try selecting SPFIB instead of Arfor. You will get a tailored version with designated TAF's instead of the whole state.

Before you print it out, look in the top left margin and click on FILE, then select Print setup.

Next select printer properties and you will be be able to specify how many pages to fit on an A4 page.
For HP laser, usually found under the "finishing" tab, for Lexmark it's the "layout" tab.
Experiment for other printers, you should find a tab that leads to the option.

If you select 2, you get two pages of the forecast per page, still quite readable.

If you've got good eyesight and really want to save some trees, select 4 pages per A4 page and landscape mode.

This will really shrink your paper use, toner or ink cartridge use and make for a tidy little package to have with you.

I picked up this great trick passing through Gove,
the local operators have been doing this for some time and were pleased to show me how.

Have fun with NAIPS, there's a few good features in there and a good help desk if you run into problems.