How to downgrade iPad NAND firmware and boot premium diags

MagicCFG have two ways to boot diags on iPad Air 1:
1. The diags of iPad mini 3 gets booted on it to enter diags mode, or
2. the NAND firmware gets downgraded and we boot iPad Air J71AP diags on it.

In this article we will focus on the second method, which seems to be difficult to understand for some people, so I'll explain it in a short tutorial :)

Information about the method:
To downgrade the NAND firmware, we do something very familiar which everybody should have done onetime with his/her device.
We basically boot an iOS 8 RAMDISK on the iPad Air, which is automatically flashing the old NAND firmware on the device to be able to create the partitions in the usually following iOS restore process. 
Since we are using irecovery to flash the bootchain, the device don't start a real restore session. It doesn't get any information to perform the restore (partition instructions or commands to flash the new rootFS to the System Partition)... 
So the existing filesystem on the device don't become wiped or updated.
It stays untouched, while the nand firmware gets downgraded, so we are able to boot the J71AP diags without any crashes :)

How to perform the Downgrade and boot the J71AP diags?

First you have to put your device in DFU mode and connect to your mac.
Open MagicCFG and go to the Diags Booting Window.
Select the "Premium diags" option and click in the middle of the round Start-Button.

After the exploit succeeded, there will be a pop-up alert which will ask you, if you want to downgrade the NAND firmware now. Click on yes

Then the NAND downgrading process should start.
It will start to boot into the ramdisk in verbose boot and show a restore screen like this:

Wait for 10 seconds, then you can safely reboot the device and set it in DFU mode again.
Go to the Diags Booting window in MagicCFG again and click the Start-Button again (Select Premium diags again of course :)

When the pop-up alert is shown again, select No

If you did all correctly, MagicCFG should boot into the diags now and show your iPad Air in a solid Yellow screen. (Maybe other colours too, if the screen is Cyan, you may made a mistake with NAND downgrading...)

Now your iPad is booted into Diags Mode, you can edit the sysCFG in MagicCFG main window...
Enjoy :)