Q: In IND, there is an RNAV (GPS) Y Rwy 5L. What is the Y? Then there is an RNAV (RNP) Z Rwy 5L. The charts are basically the same. However, on the Y chart there are three different MDAs, the first is called LPV. What is that? Then on the Z chart it specifies two different MDAs, one is with an RNP of 0.15 and the other is 0.30. I imagine this pertains to equipment that is above my pay scale.

A: 1. The “Y” and “Z” are just identifiers for multiple approaches based on the same navigation equipment to the same runway with diffrent procedures.

2. “LPV” = Localizer Precision with Vertical guidance. Under an LPV minimum you would have a “DA” in lieu of an MDA. A LPV is a GPS / RNAV procedure that utliizes a ground based system (WAAS) to get an accurate vertical location of you aircraft in addition to the satellites for the lateral in order to accurately provide a glideslope and track your progress on it based on the data it recieves. You must have a WAAS capable RNAV system on board the aircraft. It would be flown the same as an ILS down to a DA where you would go missed if you didn’t have the appropriate environment in sight. Once again, the LPV and LNAV / VNAV systems are not “dive and drive” type MDA approaches. They are flown on a glideslope to a DA just like an ILS, where a missed is required immediately upon reaching DA if the environment is not in sight.

3. “RNP” = Required Navigation Performance. It is the tolerance that the navigation equipment in your aircraft must be capable of operating within, in order to utilize the procedure. Normally there is an allowance for momentary deviations of no more than 1 times the specified RNP number. RNP .3 would be .3 nm either side of centerline meaning that the aircraft navigation system must be able to maintain that tolerance and alert the pilot if it cannot. For instance, GPS terminal mode is 2 nm either side of course or Approach mode is normally .3 nm either side.