iPadOS 11.3.1 (build 15E302) is an official Apple over-the-air update for the iPad Air 2 (Cellular), released on 2018-04-24T17:07:55Z. The update package is 735.42 MB. This is a delta (partial) update that requires 11.0.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 67057b21d2ac92b5fb7ab0dce3d3d543231f5aa4.zip.