Non-pilot question on dual gps

I just was reassigned the plane that had the GPS failure I mentioned earlier. Maintenance replaced the receiver with a new unit and it worked fine. So this was apparently a receiver malfunction, not an antenna issue.I agree that many hand-held units offer greater accuracy that the older, IFR-certified units. I still recommend to pilots that I instruct that they understand the factors that can affect GPS reliability, regardless of the vintage of the receiver or whether it is IFR-certified or WAAS capable.There are currently only two IFR-certified WAAS GPS receivers that I know of - the Garmin (nee UPS/AT) GNS 480 and one produced by Chelton Flight Systems.Even a WAAS-enabled GSP receiver can have reliability issues and pilots need to check for WAAS NOTAMs when they get a briefing. WAAS NOTAMs can be issued for a particular airport or for a wider area. A WAAS airport NOTAM usually give a time range during which LNAV/VNAV and LPV approach minimums will not be available. WAAS Area NOTAMs are issued for larger geographic areas if large ionosphere disturbances are predicted or if a ground-based WAAS Reference Station is out-of-service.GPS is great, but it's important to know the limits of any navigational equipment.