If you are within 50 NM of the top of descent, which descent mode is invoked?

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Multiple Choice

If you are within 50 NM of the top of descent, which descent mode is invoked?

Descent planning needs to start before you actually reach the top of descent so you can meet altitude constraints smoothly. When you’re within about 50 NM of the TOD, the system switches to Early Descent to begin transitioning from the cruise altitude into the published descent profile. This mode cue starts the descent using the programmed VNAV path, setting an appropriate vertical speed or flight path to reach the required altitudes at the fixes ahead without overshooting. Cruise descent isn’t the specific initiation mechanism used at this close range to TOD, because it implies a more generalized, later-stage descent. VNAV PATH is the general vertical guidance following the planned path, but Early Descent is the mode that actively initiates descent in preparation for TOD. LVL CHG hold would simply maintain or change altitude in a level-change manner, not execute the descent profile toward the runway. So, the best choice is Early Descent because it’s the designated mode for starting the descent as you approach TOD to ensure a coordinated and timely transition onto the vertical profile.

Descent planning needs to start before you actually reach the top of descent so you can meet altitude constraints smoothly. When you’re within about 50 NM of the TOD, the system switches to Early Descent to begin transitioning from the cruise altitude into the published descent profile. This mode cue starts the descent using the programmed VNAV path, setting an appropriate vertical speed or flight path to reach the required altitudes at the fixes ahead without overshooting.

Cruise descent isn’t the specific initiation mechanism used at this close range to TOD, because it implies a more generalized, later-stage descent. VNAV PATH is the general vertical guidance following the planned path, but Early Descent is the mode that actively initiates descent in preparation for TOD. LVL CHG hold would simply maintain or change altitude in a level-change manner, not execute the descent profile toward the runway.

So, the best choice is Early Descent because it’s the designated mode for starting the descent as you approach TOD to ensure a coordinated and timely transition onto the vertical profile.

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