iPadOS 11.3.1 (build 15E302) is an official Apple over-the-air update for the iPad Air (WiFi), released on 2018-04-24T17:05:05Z. The update package is 583.62 MB. This is a delta (partial) update that requires 11.2.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 99b365bc51ac5c2fea27df2d6ada7a080f709915.zip.