Always read the Release Notes for the FUS file. Cisco often hides specific hardware compatibility notes there that aren't in the main AireOS release notes. Have you run into a "PowerPC not responding" error after skipping this file? Let me know in the comments below.
Unlike a standard AireOS firmware update (which changes the operating system features), an FUS updates the —specifically the bootloader and the PowerPC boot code . air-ct2500-k9-2-0-0-0-fus.aes
Don’t panic. You haven’t downloaded the wrong file. You’ve just encountered Cisco’s . Always read the Release Notes for the FUS file