Aviation News Talk Podcast

Max tackles a common frustration among pilots: why RNAV (GPS) glide paths sometimes fail to couple with the autopilot. A recent Facebook post from a pilot flying a Cirrus SR22T triggered the discussion, as the poster encountered exactly this problem during an LPV approach, mistakenly attributing it to an expired database. Max explains that the real culprit was a fundamental misunderstanding of RNAV approach procedures. Unlike an ILS glide slope, which is a physical radio beam transmitted from ground equipment, an RNAV glide path is a computed construct generated by the aircraft’s GPS navigator. It only becomes “real” for the autopilot to couple to when flown properly, following all step-down altitudes as published. A key indicator is the glide path diamond: it remains hollow and white until the aircraft crosses the fix before the Final Approach Fix (FAF), at which point it turns solid magenta, signaling that the autopilot can engage. Max emphasizes that this behavior contrasts with ILS approaches, wher