737 VNAV descent debacle
His all,
so currently there is what seems to be a huge debate on VNAV PTH descent speed and energy management between many pilots I’m flying with and currently there are two leading trains of thought and I wanted to see what the consensus was here.
thought 1. During the descent in common VNAV (FMC U14.1) the aircraft when descending in VNAV PTH will “hang” around the FMC imputed speed/bug speed to maintain the pre calculated patch and mostly is upper winds are close enough. This means the speed will go away from the bug up and down but no pilot intervention is really needed unless the FMC DRAG REQUIRED or THRUST REQUIRED message is shown. Basically just let us do its thing.
Thought 2. VNAV PTH descent is still inherently dumb and should constantly be managed so as to never let the speed stray away from the bug speed. This thought also includes updating the VNAV calculation ever so often by putting the current top waypoint at the top again and executing the force Vnav to recalculate the path.
Basically the just is one says leave Vnav the other says micro manage because it can’t be trusted
would love to here everyone’s thoughts and also if anyone knows any Boeing published documents that would basically answer the question and put the debate to an end that would be amazing!