Flying an RNAV (GPS) approach with LNAV+V can look and feel like flying an LPV: centered needles, a glidepath diamond, and an approach mode that looks “fully coupled.” The difference is protection. LPV and LNAV/VNAV guidance is evaluated and obstacle-protected down to a decision altitude. LNAV+V is advisory vertical guidance. It can be a great stabilized descent aid to the MDA, but it is not a guarantee of obstacle clearance below minimums.

In this episode, Max analyzes the crash of N98FK, an Epic E1000, near Steamboat Springs/Bob Adams Field (KSBS). The flight came in at night into mountainous terrain with a lowering ceiling. Minutes before the accident, reported conditions still showed good visibility but broken cloud layers, and the altimeter setting was 30.16. That combination—night, terrain, and marginal weather—is exactly where “looks right on the PFD” can be a lethal trap.
KSBS has three instrument procedures. The VOR/DME-C is not authorized at night. The RNAV (GPS)-E is aligned with runway 32 but publishes only circling minimums because the descent from the last fix to the runway would require an unusually steep path. The RNAV (GPS) Z RWY 32 is the only procedure that publishes straight-in LNAV minimums, but its minimums are higher and the chart includes important restrictions and warnings that matter to this accident.
Max then walks through what the ADS-B ground track and barometric altitude data show. Laterally, the airplane flew a clean inbound path that closely matched the RNAV (GPS) Z RWY 32 final course. Vertically, the profile started out “textbook.” After correcting the baro altitudes for the 30.16 altimeter setting, the airplane crossed the FAF MABKY essentially overhead and only about 90 feet above the published at-or-above altitude (10,800 feet). It crossed the stepdown fix WDCHK essentially on altitude as well, only about 15 feet above the published at-or-above 9,100 feet (the MDA).
And then it didn’t level off. Instead of holding 9,100 feet until the runway environment was in sight and the pilot was legally and safely able to continue, the airplane kept descending. The last recorded point was around 8,240 feet—roughly 860 feet below the MDA—near terrain that tops out around 8,250 feet on Emerald Mountain. The descent angle stayed remarkably consistent from the intermediate segment through impact, with no sign of an MDA level-off. That consistency fits a common scenario: the autopilot was coupled to the LNAV+V advisory glidepath and simply kept flying down the path.
That leads to the legal and practical heart of the episode: when can you descend below an MDA on a nonprecision approach? Max reviews the three requirements in 91.175(c): the required flight visibility, at least one specified visual reference for the intended runway distinctly visible and identifiable, and being continuously in a position to land using normal maneuvers and a normal rate of descent. Until those are true, you level at MDA. Full stop. “But I’m on the glidepath” is not a criterion.
Max also explains why pilots get surprised by +V. Many expect the autopilot to capture altitude at MDA. But if you’re coupled to any glidepath, many autopilots will continue down the path unless you command a level-off. If you want to stop at MDA, you must actively select a vertical mode that holds altitude at the right time. That’s a systems/automation issue layered on top of the fundamental decision-making issue: don’t descend below minimums without the required cues and clearance.
Finally, Max decodes a chart note that many pilots gloss over: “Visual Segment – Obstacles” and, on some charts, “34:1 is not clear.” Those are warnings that obstacles penetrate the visual segment evaluation surface. In plain English, the visual segment may not be clear of terrain if you descend below MDA before you have the runway environment and can maneuver visually. Max discusses how the FAA’s 34:1 and 20:1 concepts relate to obstacle evaluation in the visual segment, and why these notes matter most at night and in mountainous terrain, when you may not see the hazard until it is too late.
To drive it home, Max recounts flying the same RNAV (GPS) Z RWY 32 in a simulator and hitting the same mountain when the autopilot was coupled to the advisory glidepath. He also explains why moving-map “relative terrain” may not save you: alerts can come late, and the colors can lull you into thinking you’re protected when you’re not.
If you fly IFR—especially in mountainous terrain—treat LNAV+V as a stabilized descent tool to the MDA, brief the notes, know what your autopilot will do at minimums, and deliberately transition to a level-at-MDA mindset unless and until you truly have the runway environment and can land normally.
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