iPadOS 11.2.1 (build 15C153) is an official Apple over-the-air update for the iPad Air (China), released on 2017-12-13T18:04:37Z. The update package is 327.24 MB. This is a delta (partial) update that requires 11.1.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 74c32e552939b2f94059fab254fa470ddcb43492.zip.