If the AP experiences a firmware failure or a corrupt firmware image, indicated by three red LED indicators, you must reload the image from a connected TFTP server. The fopllowing document explains the process of reloiading image from tftp server using CLI.
The same document also explains how this can be done using MODE button and GUI. Go through this document fully. This will definitely have an answer for your problem. In MODE button, first all LEDs will turn Green followed by status LED blinking green. Wait until this happens.
Transferring Crash file from standby: Login to the Active WLC in HA.
From CLI: (Cisco Controller) >transfer upload datatype crash (Cisco
Controller) >transfer upload filename (Cisco
Controller) >transfer upload mode tftp (Cisco Controller) >transfer
This is the start of a display filter cross reference between Wireshark
and OmniPeek. The 1st installment is a table of advanced filters. More
filters will be added as time allows. It is a living doc, so check back
for changes every so often Please feel f...