Copyright D.P. Browne 2011

Descent Vertical Deviation

When the aircraft enters the descent phase, the Progress page shows the Descent VDEV value. This is the amount in feet, that the aircraft is above or below the descent profile. The PFD shows the value as a magenta circle on the left of the altitude tape..

During the descent monitor the VDEV displayed on the PFD and the value displayed on the progress page

During the descent the A/P vertical mode operates a speed on elevator control law as the A/T reduces the thrust to idle. This will result in a glide path that should match the decent profile path. If the VDEV becomes to great, and shows the aircraft below the decent profile path, the A/P will change mode to a V/S type mode and maintain -1000 ft/min, whilst the A/T will maintain the target speed. In these cases, the path intercept symbol              may appear. The decent phase ends when flying over the (DECEL) waypoint