Ipad Air Crashing and Won't Update

If you own a full computer, you could try connecting your iPad Air to a full computer, connected to the Internet, and using the latest version of iTunes for the computer, let iTunes do the update of your iPad Air to iOS 12.4.6, instead.

Good Luck to You!

Have you tried a hard reset of your iPad by holding down both the Home and sleep/wake buttons simultaneously until your iPad goes to black and restarts with Apple logo, then release the buttons?

Good Luck!

What version of iOS is your iPad Air currently running?

At this point, I suggest contacting/reaching out to Apple Product support and services.

Tap on the first link below and scroll down some to get to the Apple Product Support section and phone numbers for your location/region.

https://www.apple.com/contact/

OR

https://support.apple.com/en-us/HT201232

Best of Luck to You!