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Where specifically in an airplane’s documents can I see if it is equipped with baro aiding and/or WAAS?

Asked by: 7994 views , , ,
Aircraft Systems, FAA Regulations, Instrument Rating

Just having a bit of trouble finding this stuff.  Bonus question... where in the regs does it say that you don't have to do a RAIM check with WAAS?  I can make assumptions, but I haven't found anything that explicitly says you don't have to.

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3 Answers



  1. Mark Kolber on Feb 09, 2014

    Regular question: in the POH supplement for the GPS unit or the RNAV Baro unit (hint; if you’e talking about anything other than the airlines, chances are you do not have Baro VNAV.

    Bonus question: Nowhere. If you look at the definition of “Suitable RNAV system” in FAR 1.1, you will see the FAA wisely (because technology changes faster than the regulatory process) left the details of what constitutes such a system to other sources: “Information on suitable RNAV systems is published in FAA guidance material.” (my emphasis). That includes the AIM, ACs, Orders, etc…

    As some folks are more than happy to remind us from time to time, the AIM is “not regulatory.” But it is “guidance material.” So, for example, AIM 1-1-8(a)(3) tells us

    ==============================
    3. Receiver Autonomous Integrity Monitoring (RAIM). When GNSS equipment is not using integrity information from WAAS or LAAS, the GPS navigation receiver using RAIM provides GPS signal integrity monitoring. RAIM is necessary…
    ==============================

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  2. John D Collins on Feb 10, 2014

    The information you seek should be in your AFMS for the equipment. The limitations section is regulatory. In summary, a WAAS GPS does not use RAIM as long as it is receiving the WAAS (SBAS) satellites, but does when it is operating outside of the WAAS service volume. The SBAS is the technical term for Space Based Augmentation System of which WAAS is the example in North America. In Europe, they have an SBAS system called EGNOS. These SBAS systems are completely compatible with one another.

    Here is an excerpt from the Garmin GNS530W AFMS Limitation Section:

    2.5 Flight Planning

    For flight planning purposes, in areas where SBAS coverage is not available, the flight crew must check RAIM availability. Within the United States, RAIM availability can be determined using the Garmin WFDE Prediction program, Garmin part number 006-A0154-04 software version 3.00 or later approved version with Garmin approved antennas or the FAA’s enroute and terminal RAIM prediction website: http://www.raimprediction.net, or by contacting a Flight Service Station. Within Europe, RAIM availability can be determined using the Garmin WFDE Prediction program or Europe’s AUGER GPS RAIM Prediction Tool at http://augur.ecacnav.com/augur/app/home. For other areas, use the Garmin WFDE Prediction program.

    This RAIM availability requirement is not necessary if SBAS coverage is confirmed to be available along the entire route of flight.

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  3. John D Collins on Feb 16, 2014

    You won’t find any information in the POH or AFMS regarding Baro Aiding. This term is used to mean that the RAIM algorithm uses the pressure altitude input, usually from an encoding altimeter. By knowing the current pressure altitude (29.92), the RAIM algorithm can function with one less satellite as an input and determine if the current value of the RAIM calculation is suitable for use. Since the tightest RAIM requirement is for a non precision approach, the position value must be contained within 1822 feet laterally. Part of the position calculation includes the GPS altitude and as long as the difference between it and the pressure altitude is within limits, then the position can be used for an approach. All modern IFR GPS units use Baro-Aiding and this has nothing to do with WAAS.

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