I have tried the iCal connector to Google Calendar. It is a very useful feature and I was very happy when I saw it but, unfortunately, it looks like Google is not properly updating the information.
The first time you make the connection it works fine but afterwards, if you make changes in the database, these changes are not reflected in Google Calendar. If you try to connect it again you must introduce something new in the URL provided by Airtable so that Google Calendar understand it is a new Calendar and does not use the cache.
So, the calendar is out of sync as soon as you change any information in the database.
Althouhg I think this is a Google problem (there are some forum about it https://productforums.google.com/forum/#!topic/calendar/ixQnzHmWDSk), it would be fantastic if you could do something about it because this feature is something we have been looking for.