iPadOS 11.2.1 (build 15C153) is an official Apple over-the-air update for the iPad Air (Cellular), released on 2017-12-13T18:03:56Z. The update package is 1.07 GB. This is a delta (partial) update that requires 10.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 6743786e340e22080b7829672ca757932e0b9945.zip.