My work experience in configuring Cisco Wireless AP. Here are some of my most used commands.

How to configure your AP to connect to WLC

How to check IP

show capwap ip config

Check CAPWAP Join Status

show capwap client config

Load Firmware from TFTP server

ap: set IP_ADDR 10.1.128.120
ap: set NETMASK 255.255.255.0
ap: set DEFAULT_ROUTER 10.1.128.1
ap: set TFTP_SERVER 10.1.250.46
ap: set TFTP_FILE ap3g2-k9w8-tar.default

ap: tftp_init
ap: ether_init
ap: flash_init
ap: tar -xtract tftp://10.1.250.46/ap3g2-k9w8-tar.default flash:
ap: boot

Additional Possible commands

uboot>> setenv ipaddr 10.1.128.120        # AP’s IP
uboot>> setenv serverip 10.1.250.46       # TFTP server IP (your PC)
uboot>> setenv netmask 255.255.255.0
setenv gatewayip 10.1.128.1

uboot>> printenv


uboot>> tftpboot 0x80000000 ap3g3-k9w8-tar.default


uboot>> bootm 0x80000000

When already inside the AP IOS

AP# archive download-sw /overwrite /force-reload tftp://10.1.250.46/ap3g3-k9w8-tar.default
archive download-sw /overwrite /force-reload tftp://10.1.250.46/AIR-AP1830-K9-8-10-196-0.tar
archive download-sw /overwrite /force-reload tftp://10.1.250.46/AIR-AP1830-K9-8-10-196-0.tar

No need to force.. Just download and load.
Archive download-sw /reload tftp://10.1.250.46/AIR-AP1830-K9-8-10-196-0.tar