While this is primarily found in larger aircraft, if you have ever flown a non-precision RNAV (GPS) approach to LNAV minimums with advisory vertical guidance (LNAV+V) in a light aircraft, you are relying on data generated from the vertical descent angle
According to the SAIB referenced in the sidebar on the opposite page, "The published vertical descent angle
and navigation equipment-generated advisory vertical guidance offers no guarantee of meeting altitude constraints.
Until the avionics manufacturers can revise and distribute new operating system software, the FAA's SAIB strongly suggests "operators and pilots carefully review departure, destination and alternate airport IAPs during pre-flight" and, for IAPs lacking a vertical descent angle
as charted above, using another IAP "not affected by this airworthiness concern.
With all the talk of continuous descent non-precision approach techniques and vertical descent angles
, you might think there's no place for dive-n-drive.
Advisory glidepath guidance can be generated by some avionics systems based on the vertical descent angle (VDA) published for the procedure, which is the angle between the final approach fix at its crossing altitude and the runway at its threshold crossing height.
The first step taken by the FAA to mitigate the risk of following an advisory glidepath into an area with particularly hazardous visual area obstacles along the vertical descent angle was to simply remove the vertical descent angle.
The presence of vertical descent angles had previously been considered an unambiguous safety benefit, and tightly integrated into procedure coding and publication.
This has led to a lot of confusion as is well documented in Lee Smith's excellent articles on vertical descent angles
in March and June.
As a result of an NTSB recommendation following the controlled flight into terrain of American 1572 on approach into Windsor Locks, Connecticut, (BDL) in 1995, the FAA began to add vertical descent angle information to instrument approaches in 1998 in order to encourage stabilized approaches.
On this approach, a typical GPS would give the pilot an LNAV+V indication, for which a computed glidepath based on the published vertical descent angle is provided for advisory purposes.
The chart shows a Vertical Descent Angle
(VDA) of 3.