Although they look alike, there is a world of difference between ILS, LNAV+V and LNAV/VNAV glidepaths. It turns out that not all glidepaths are created equal.
Advisory glidepaths (VDAs) on non-precision approaches do not guarantee obstacle clearance below the Minimum Descent Altitude (MDA), a widespread misconception leading to safety hazards.
Pilots must understand they are solely responsible for obstacle clearance past the Missed Approach Point (MAP) when using an advisory glidepath, as avionics display it to the runway regardless of terrain.
To address this, the FAA is removing VDA information from charts where obstacle clearance is not assured below the MAP, while approved commercial operators may use "Derived DAs" under specific, obstacle-protected conditions.
In March, we examined the hazard of following a non-precision visual descent angle (VDA) below the MDA. This is easy to do because flying a non-precision approach with an advisory glidepath looks similar to an ILS, LPV or LNAV/VNAV with a real glidepath.
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