Originally Posted by
Stan Woolley
If I remember correctly when VNAV is being used the bug automatically reduces to the speed when the new setting is made on the flap handle
Originally Posted by
D-OCHO
VNAV reduces the speed in reference to the actual flap setting. For example when the flap is half way between 2 settings the speed is also half way.
Nearly correct.
VNAV commands the new speed WHEN flap gauge indicates flap selection.
When flaps 1 is selected, flaps 1 will be selected on speed tape WHEN flaps 1 is reached by flaps indicator.
Cause for some confusion to this, as described misinterpretation by D-OCHO's post, is when transitioning from 1-5, where the flap lever passes the (usually non selected) flaps 2 position, so when flap 2 is passed on the flaps gauge the speed bug will temporarily bug flap 2 speed, before placing bug at flaps 5 when that selection is reached.
Next time in simulator, try selecting landing flaps from up and monitor speed bug with VNAV connected, it will step down in steps of -20/10 its continuously as flap position indicator passes flap positions.
Originally Posted by Centaurus
Their rationale is that if an asymmetric flap occurs during extension, it is best to have the higher speed for controllability reasons rather than the lower speed for the planned for final setting.
You are exactly correct, it is rational, and so this is what VNAV logic does as well, so why not embed it into SOP for manual flight or non-VNAV flying.
VNAV protects the aircraft, its functions are rational and logical.
It works on the most known principle of automation: input->output, therefore flaps gauge input->flap speed bugged.
The above also results in the biggest problem using VNAV: {not so good smelling pieces} in-> {worse smelling pieces} out, consternating pilots in the process what's happening and then starting to not trust VNAV.