What is the reason you want to blank the lower CDU as part of the before taxi flow? And when would you normally switch it back ON?

They don't want the pilot looking down during taxi, or texting from their cell phones. I'm kidding about the cell phones, but I remember reading they don't want pilots distracted by keeping their head down.

I figured it would be something like that but still I find it a bit odd if that is the only reason because one would like to belive pilots of nature are very focused persons knowing what to look at at any specific time :(

First off, that's not a CDU, that's just the lower DU :PIt's so the pilots don't have as much data to deal with during crucial stages of the flight such as takeoff. The data that normally goes to the lower display unit is not crucial to that stage of the flight.

If something goes wrong it'll turn on automatically catching the pilots attention.Sorry for double post but the pone doesn't let me edit.It usually stays off all the time during all flight phases

Thanks for the input! So what you say is that normally you only use this lower DU :( during the engine start procedure?

And during flight control check. I never see them used in flight. You may however use the compact engine displays. But other than that, after takeoff the lower DU seems to have done its duty.

Like Carlos said it's blanked because if something bad happens like a failure of some sort it will automatically turn itself back on alerting the crew that something is wrong

I didn't know that but guess you'll never stop learning new stuff about this a/c :(