Looks like you may need to replace the connector on the arm because the "keeper" or "retainer" on the bottom came off. I recommend these:

http://www2.towerhobbies.com/cgi-bin...?&I=LXD929&P=0

These are tightened with an allen wrench and work well. You may have to drill the wire hole to fit the wire which is probably metric. Also, use the metal included retainer not the plastic one, it holds tighter. You will need to remove the arm from the servo to install the device and then reinstall. Do the drilling while it is off. hold with pliers being careful of fingers. You should be able to get these or very similar at LHS. Be careful when resetting rudder and nose wheel centers. Let instructor know you had this apart so he will doublecheck your work.

Good luck