iPadOS 11.2.1 (build 15C153) is an official Apple over-the-air update for the iPad Air (Cellular), released on 2017-12-13T18:04:14Z. The update package is 51.63 MB. This is a delta (partial) update that requires 11.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: b249ceb3d49390abc1fa873413280569691b992a.zip.