White screen iPad Air and the process repeats again and again from black screen to again white

It might be a hardware issue, in which case you need to take your device to an Apple Store for evaluation.

To rule out software issues, try these standard troubleshooting steps.

Reset: hold down the Home and Power buttons until you see the Apple logo (10-20 seconds).

If this doesn't help, you might need to Restore your iPhone: https://support.apple.com/en-us/HT204184

If your backup is to iTunes, make sure it's an encrypted backup.