![]() ![]() ![]() That was for planning and filing purposes only. Since RNAV approaches flown to LPV minima are not technically precision approaches, all RNAV (GPS) approaches are considered non-precision therefore, the standard non-precision minimums apply: 800-2. This means that when we are selecting an alternate field, we are really selecting a particular approach to an expected runway. The standard alternate minimums for planning purposes is 600-2 for precision approaches and 800-2 for non-precision approaches. Typically alternates are selected based on weather conditions at the ETA at the alternate. Without getting into the whole discussion of alternates, there is one area that is relevant. For a light GA airplane, 50 feet would be a reasonable tolerance. Don’t be surprised if you receive a quizzical look. For instrument students getting ready for the instrument practical or instrument pilots doing an IPC (instrument proficiency check), ask the examiner or CFII how much he or she will allow you to go below the DA when executing a missed approach. The standards for DH are not specified in tolerances but the pilot must “immediately initiate the missed approach…” This means that the regulations allow the airplane to descend below DA during the miss. This means it is a “hard” altitude: Thou shall not go below unless one of the 10 items in 91.175(c) is visible. In the Instrument Rating ACS (Airman Certification Standards), the MDA standards are +100 feet and -0 feet once at the MDA. The MDA (minimum descent altitude) is associated with non-precision approaches and the DA is for precision approaches-this time including RNAV APV approaches. While both are decision altitudes, at some point during an approach, we decide to continue the approach to the runway and land or declare a missed approach. Bottom line: there is almost always an electronic glideslope lurking in the shadows. An LP (localizer performance) approach is a non-precision RNAV approach that requires WAAS. The “+V” refers to the advisory glideslope. Furthermore, some WAAS navigators often provide an advisory glideslope to non-precision RNAV approaches: LNAV+V and LP+V. ![]() TodayĪs we move forward in time with the proliferation of LPV approaches, the phaseout of non-precision approaches using ground-based navaids such as VOR, NDB, and LOC-only will result in fewer and fewer non-precision approaches. I will refer to them using the more common terms: LPV approaches and LNAV approaches. Similarly, there are no “LNAV” approaches. It is an RNAV (GPS) approach flown to an LPV DA. While we use the term “LPV approach,” there is no such thing. We’ll focus on the LPV approaches, but first a clarification. and are flown to LPV DA(H) to create an electronic glideslope. APV-SBAS uses the satellite-based augmentation system (SBAS) that we call WAAS in the U.S. Typically, WAAS-equipped airplanes no longer have the required equipment to fly APV-Baro approaches. The former uses barometric input to fly the GS and are flown to an LNAV/VNAV DA(H) (decision altitude MSL, or decision height, AGL). There are two flavors of APVs APV-Baro and APV-SBAS. So, while flying an APV might be good practice for flying an ILS, none of those APV approaches-thus most GPS approaches-provide meaningful practice for non-precision approaches. On the other hand, due to some technical differences that are immaterial to pilots, most RNAV (GPS) approaches with WAAS have an electronic glideslope and are referred to as APV (approaches with vertical guidance).įor practical purposes, APV approaches are flown similarly to an ILS. I say “precision-like” approaches because the only true precision approach available to us is the ILS with a ground-based glideslope transmitter. The result is more precision-like approaches which undoubtedly improves safety. Today in the U.S., with WAAS (wide area augmentation system), the reduction of VORs and the near elimination of NDBs, there are fewer and fewer available non-precision approaches. With the advent of GPS approaches in the 1990’s and early 2000’s, we had many more opportunities to practice and fly non-precision approaches. ![]()
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