iPadOS 11.3.1 (build 15E302) is an official Apple over-the-air update for the iPad Air 2 (Cellular), released on 2018-04-24T17:07:57Z. The update package is 608.41 MB. This is a delta (partial) update that requires 11.2.6 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 9ba12eee64c64e725647501318eb9275cf54cae0.zip.