it sounds like you have the gear switch/lever in the up position, i'm not a futaba user but i would say your channel five switch, whatever one that is. is reversed. if you fly and crash a retract plane and forget to put the gear down again while the plane loads again the plane will just put the gear up and crash right on the runway.

if it is reversed just go into the control options and tick the reverse box for that channel. an easy way to check it flick all your swithes the opposite from where they are now and see if the gear stays down. then one by one flick them all back untill the gear goes up. make a note of the channel and reverse this switch in the control menu of AFP.

cheers