[~] airmon-ng start ath0

usage: airmon-ng <start|stop> <interface> [channel]

Interface       Chipset         Driver

ath0            Atheros         madwifi-ng VAP (parent: wifi0)
wifi0           Atheros         madwifi-ng

[~] airodump-ng -w test02 -c 2 ath0
ioctl(SIOCSIWMODE) failed: Invalid argument
Error setting monitor mode on ath0
[~] airmon-ng start ath0

usage: airmon-ng <start|stop> <interface> [channel]

Interface       Chipset         Driver

ath0            Atheros         madwifi-ng VAP (parent: wifi0)
wifi0           Atheros         madwifi-ng

[~] airmon-ng start wifi0

usage: airmon-ng <start|stop> <interface> [channel]

Interface       Chipset         Driver

ath0            Atheros         madwifi-ng VAP (parent: wifi0)
wifi0           Atheros         madwifi-ng (monitor mode enabled)

[~] airodump-ng -w test02 -c 2 ath0
ioctl(SIOCSIWMODE) failed: Invalid argument
Error setting monitor mode on ath0
[~] airodump-ng -w test02 -c 2 wifi0
ioctl(SIOCSIWMODE) failed: Invalid argument
Error setting monitor mode on wifi0
[~] airodump-ng -w test02 -c 2 ath0
ioctl(SIOCSIWMODE) failed: Invalid argument
Error setting monitor mode on ath0