Narrative:

Mdw was using one of the new RNAV GPS approaches; RNAV (GPS) Z runway 22L. No problem; we have a relatively new universal 1FW with waas. Loaded up the approach and noticed that even though the approach seemed to load normally with all of the waypoints and banners; needed for the approach; once loaded it did not show that an approach was loaded into the FMS on the navigation page 1. I was not able to arm or activate it--as would be correct since the FMS was not showing the approach as loaded on the navigation page; yet there it was in all of its glory on the fltplan page. Since it was VFR we ended up being assigned traffic to follow and it became a non-event. When we returned to our home base I contacted the FMS manufacturer and spoke to our trainer. I asked him why it would not work and I ended up performing a maintenance download. We have a dual FMS installation and both were operating identically. Upon further questioning it was determined that the approach we were trying to do was an lp [localizer performance (without vertical guidance)] approach although we were not aware of this. After doing more research we discovered that even though our FMS is waas certified; this particular approach came out after it was certified. Universal did not want to do the paperwork to recertify it for these approaches; but included them in the database and labeled them with an (a) [appended to the left of the approach designator in the FMS 'list of approaches']. I discovered this on one of my many calls with our trainer discussing this issue after the event. These are labeled with the (a) [to denote them] as an advisory or advanced approach. This [status allows selection and display] of everything in there but we are unable to arm and activate it. Our FMS is not certified for these lp approaches although it is waas certified for lpv approaches. Since it is lpv waas certified it has this approach in the database. Interestingly; I contacted a flight test pilot that I know with [another FMS manufacturer] and their avionics systems do the same thing.big problem is the approach chart. I thought; through some research on lp approaches; they were supposed to have 'lp' in their [title]; but they do not. It just says RNAV (GPS) Z runway 22L. Only in the minimums sections do you discover that there is something different about this. Also; you just can't revert back to an LNAV approach even though it is listed as such on the approach plate because we still don't have any guidance or approach criteria from the FMS! Now this is a dilemma as we were lucky enough to discover [the problem] while we were VFR but I certainly wouldn't have wanted to find this out IFR amongst the tall buildings in chicago and I'll bet in the future when we have to decline this approach we won't be ATC's best friend. This is a big problem as there are some 500 of these approaches out there waiting to bite the unsuspecting aviator who thinks that their waas GPS will fly anything. Something needs to be done to get the word out as I raised a huge red flag with universal and maybe with rockwell but now that these approaches are there and the waas gpss can fly them; maybe yes and maybe no and there is no reversion to LNAV for those that can't but still have a waas GPS. At least I know what to look for on the RNAV approach plates; so I won't fall into this trap; but I'll bet that there are quite a few [pilots] that don't.how is that for a gotcha!

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Original NASA ASRS Text

Title: A corporate jet flight crew cleared to fly the RNAV (GPS) 22L approach to MDW discovered that; although the approach was in their FMS database and could be loaded it could not be executed and utilized to fly the approach. The flight was in VMC and continued the approach landing uneventfully. Subsequent inquiries determined the approach utilized LP (Localizer Performance) minimums and that; although present in the database; had not been certified for use by the manufacturer due to their late availability just after the hardware/software itself had been certified.

Narrative: MDW was using one of the new RNAV GPS approaches; RNAV (GPS) Z Runway 22L. No problem; we have a relatively new Universal 1FW with WAAS. Loaded up the approach and noticed that even though the approach seemed to load normally with all of the waypoints and banners; needed for the approach; once loaded it did not show that an approach was loaded into the FMS on the NAV page 1. I was not able to arm or activate it--as would be correct since the FMS was not showing the approach as loaded on the NAV page; yet there it was in all of its glory on the FLTPLAN page. Since it was VFR we ended up being assigned traffic to follow and it became a non-event. When we returned to our home base I contacted the FMS manufacturer and spoke to our trainer. I asked him why it would not work and I ended up performing a maintenance download. We have a dual FMS installation and both were operating identically. Upon further questioning it was determined that the approach we were trying to do was an LP [Localizer Performance (without Vertical Guidance)] approach although we were not aware of this. After doing more research we discovered that even though our FMS is WAAS certified; this particular approach came out after it was certified. Universal did not want to do the paperwork to recertify it for these approaches; but included them in the database and labeled them with an (a) [appended to the left of the approach designator in the FMS 'list of approaches']. I discovered this on one of my many calls with our trainer discussing this issue after the event. These are labeled with the (a) [to denote them] as an advisory or advanced approach. This [status allows selection and display] of everything in there but we are unable to arm and activate it. Our FMS is not certified for these LP approaches although it is WAAS certified for LPV approaches. Since it is LPV WAAS certified it has this approach in the database. Interestingly; I contacted a flight test pilot that I know with [another FMS manufacturer] and their avionics systems do the same thing.Big problem is the approach chart. I thought; through some research on LP approaches; they were supposed to have 'LP' in their [title]; but they do not. It just says RNAV (GPS) Z Runway 22L. Only in the minimums sections do you discover that there is something different about this. Also; you just can't revert back to an LNAV approach even though it is listed as such on the approach plate because we still don't have any guidance or approach criteria from the FMS! Now this is a dilemma as we were lucky enough to discover [the problem] while we were VFR but I certainly wouldn't have wanted to find this out IFR amongst the tall buildings in Chicago and I'll bet in the future when we have to decline this approach we won't be ATC's best friend. This is a big problem as there are some 500 of these approaches out there waiting to bite the unsuspecting aviator who thinks that their WAAS GPS will fly anything. Something needs to be done to get the word out as I raised a huge red flag with Universal and maybe with Rockwell but now that these approaches are there and the WAAS GPSs can fly them; maybe yes and maybe no and there is no reversion to LNAV for those that can't but still have a WAAS GPS. At least I know what to look for on the RNAV approach plates; so I won't fall into this trap; but I'll bet that there are quite a few [pilots] that don't.How is that for a gotcha!

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.