Many GPS approaches have lower descent minimums labeled LPV. How do I know if my aircraft is equipped to allow me to fly to those LPV minimums? And while we're at it, it would be good to know which minimums to use from the whole array of minimums found on GPS approaches.
There are many websites / blog pages that compare and contrast the different approaches. All you need to do is google a bit.
That said, if your plane can fly LPV approaches you'd know that. It requires WAAS-quality GPS receiver, and to install that requires at least a logbook entry.
Note that it's not only a matter of equipment. Even when the plane is equipped to fly LPV approaches, there can be certain conditions when you can't use LPV minimums (satellites, etc.) If you CAN use LPV minimums, the GPS unit MUST show you "LPV" in the annunciator window. It's possible that you're LPV-equipped, but your annunciator window shows you only "LNAV", for example.
So, check your documents, talk to your mechanic, you wouldn't really NOT know if your plane was ever upgraded for LPV approaches. If it's your own, you'd know and have discussed it and most likely given the mechanic the task to upgrade it. If it's a rental, or you're just buying it, look at the logs and ask the seller. And keep in mind, the annunciator window will show you the lowest GPS approach type that it senses is safe. Usually on an LPV-equipped plane that will be "LPV", but it's entirely possible it will only show "LNAV", or something else. For you to use LPV minimums also depends on the actual flight condition.
The previous answer nailed it on the regulatory/technical capacity to fly LPV, but then we have the operational capacity. LPV approaches are the most stringent for SBAS/WAAS usage. They depend not only on having enough GPS satellites in view but also that those satellites have the top accuracy status (which is dynamic and depends on how many ground stations are seeing the satellite and if the satellite is operating in perfect health). Its possible to do a predictive WAAS status prediction to find out if LPV accuracy should be available at your estimated time of arrival. Meaning if the GPS satellite constellation is expect to be good, excluding satellites which are bad or planned maintenance outages. But this doesn't assure something unexpected won't happen by the time you actually fly the approach. LPVs can also be downrated from their published minima to 250DH minima if the geometry is good enough for 250DH but not for the actual DH (assuming of course the DH is lower than 250ft). I suggest looking at the http://www.nstb.tc.faa.gov site. It's an official FAA site that has a realtime LPV200/LPV/VNAV plot (http://www.nstb.tc.faa.gov/RT_VerticalProtectionLevel.htm). This is what's going on right now. LPV200 is the full LPV down to 200DH if a approach allows (inside the yellow contour line). LPV is the downrated 250ft DH LPV (between the yellow and red contours). We also have the daily (past) plot of: http://www.nstb.tc.faa.gov/24Hr_WaasLPV200.htm - LPV200 http://www.nstb.tc.faa.gov/24Hr_WaasLPV.htm - LPV250 http://www.nstb.tc.faa.gov/24Hr_WaasLP.htm - LP
LPV is highly dependent on the iono correction grid. If there's a severe problem in the ionosphere, LPV200 and 250 could be disrupted. This is very rare and more likely up in Alaska.
For instance its normal to have outages in the California cost for a few minutes nearly every day. Its the result of instants when there are enough satellites in view, but the reference stations don't have enough satellites to properly calculate the iono grid for the nearby ocean (iono grids are used for the region where the signal travels through the ionosphere rather than for your ground location, which changes quite a bit for satellites closer to the horizon or even on a 45 degree angle).
In the future dual frequency and multi constellation SBAS will pretty much put this to end permanently. Instead of using only US GPS, Europe Galileo, Russian Glonass and others will be allowed, as well as having the receivers do the iono calculations by themselves using L1+L5 (GPS/Galileo) and L1+L3 (Glonass). This will require new receivers for most GA aircraft but is not expected to be mandated since LP/LPV already works extremely well. But it would enable LPV/LP in Hawaii, 100% of Alaska, as well as all of Central/South America.