RAIM Forecast Check - AC90-100a - Non US Operations w/N Reg

[jtr]

I'm involved in technical support for a fleet of various reg. biz jets. one of our guys on an N reg. has asked about RAIM forecasts for his A/C.

In this instance it has dual TSO-145 GPS units (Collins 4000S from memory) as well as dual/triple IRS/FMS.

AC90-100ahttp://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/0/5c94e4f44ba319a98625729c00612f37/$FILE/AC%2090-100A.pdf states(6) If TSO-C145/C146 equipment is used to satisfy the RNAV requirement, the pilot/ operator need not perform the prediction if WAAS coverage is confirmed to be available along the entire route of flight.
NOTE: Outside the U.S. or in areas where WAAS coverage is not available, operators using TSO-C145/C146 receivers are required to check GPS RAIM availability.

Can anyone point me to a different reference that demonstrates that when the GNSS system is used and is NOT the sole means of navigation (i.e. this a/c has IRSx3) the RAIM forecast is not required for TSO 145 systems OUTSIDE the US?


Thanks in return. Apologies for any poor understanding in advance - this is not usually my bag.

[ahramin]

I don't think any such reference exists. Either the GPS is required and you have to follow the RAIM checking requirements, or it isn't required and you don't. Doesn't matter if it's used or not, the question is: Is it used to satisfy the RNAV requirement?

If your RNP requires the GPS, then you are using it and will need to meet the RAIM requirements. Easy way to check this is that if you MEL the GPS receiver(s), does it affect your RNP? Can the aircraft still meet all navigation requirements without a working GPS? If so, GPS isn't being used to satisfy the RNAV requirements.

As an example, our aircraft are RNP10 for 5.6 hours from last position update when IRS only.

[FlightPathOBN]

Depends on what you are using it for.

RNP approach requires a RAIM check/prediction prior to dispatch to show availability. If the RAIM prediction for the approach is not sufficient for the RNP level prior to dispath, it cannot be used in the flight plan.
The pilot may also be required to perform a RAIM check enroute, depending on the RNP level at the final

There is enroute RAIM prediction as well, but with the RNP levels, it usually not an issue.

The system RAIM is always working, giving you the actual vs needed HIL/HPA levels, and will warn when the actual is greater than the required.

The WAAS check is a little different, as the WAAS prediction gives the geographic area of the RNP level, such as RNP 0.3, with the HPL, and the LPV percentage coverage.

RAIM/WAAS Check (http://operationsbasednavigation.com/operations-based-navigation/463-2/)