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 (LNAV+V) on non-precision approaches, while facilitating continuous descents, do *not* guarantee obstacle clearance below the Minimum Descent Altitude (MDA), unlike precision approaches with true glidepaths.
This can lead pilots to mistakenly descend unsafely below the MDA, a widespread problem prompting the FAA to remove VDA information from charts where obstacle clearance is not assured.
Pilots must recognize that advisory glidepaths are for guidance only; they retain full responsibility for obstacle clearance below the MAP/MDA and must initiate a missed approach above the MDA on most non-precision procedures.
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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