After the Sierra 10.13.3 update the AirPort Utility does not back up

Just to make sure you know what does which..

Airport utility is for setting up and checking the Airport routers.. I am guessing you are using a Time Capsule.. please clarify.

Backup on the Mac is done by Time Machine.. it is particularly flakey since sierra and worse in high sierra.

The MBA probably has SSD hard disk that will be automagically changed to APFS format during the upgrade. This does lead to all kinds of problems. Backup being a primary one.

Questions/suggestions.

1. Does Airport Utility no longer show the Time Capsule??

2. Try and see if you can mount the TC hard disk in Finder. Tell me if it fails.

3. Is your wireless configured in the computer with IPv6 set to link-local only.

Any screenshots are muchly appreciated.

4. It is sometimes necessary to scrap the existing backup and start over. Do you want to save what you have now?

5. To get time machine running again not only do you need to scrap the old backup (or archive it) you might also need to reset Time Machine.. which is not a function built into the app..

See Re: Time Capsule backing up one computer but not the other

5. Big one.

The Time Machine backup to network target is now so unreliable it is irrational to continue to still use it. We can help you get it going again.. but it is likely to fail again inside a week.

Are you prepared to buy a 3rd party backup like Carbon Copy Cloner.. which WE strongly recommend. (no financial ties)?