drift down speed?

[number]

Can anyone give me the definition of Drift Down Speed?
What is it for? Any practical example of its meaning?
thank you

[Jetdriver]

As one of my fellow moderators has kindly pointed out, you have already asked this in the Tech Log forum. You are receiving replies so I do not know why you feel the need to repeat the question here.

Now where did i put the padlock ?.......Ah yes !