I am sorry but we found the free license versions may cause a crash when it can't get ads from Google server. Both 3.5.0 free version for iPad and 1.0.0 free version for iPhone may have this bug.
Google reports that admob 6.7.0 sdk crashes when enters into airplane mode. Some customers report that it also crashes when enters into offline, i.e., when wifi signal is weak.
In-App Purchase customers including 0.99$ term license users have no such a problem because of no ads.
On 7th February, we already uploaded the bug-fixed 3.5.1 update for iPad & 1.0.1 for iPhone with admob 6.8.0 sdk so that please wait until Apple finishes their reviews.
If you are using the free license versions, please keep the online if possible and don't use airplane mode until the bug-fixed updates are available.
Again, I am really sorry for your inconvenience.
Have a great day~