Master of Acrobatic Flight

[Panzergranate]

I accidentally managed it on my first day with the game on the 360.

The best aircraft to flat spin is the I-153 in realistic or simulator mode, as they are notorious for this in real life and in the game. You'll need a bout 12,000 Feet to recover.

Taking the I-153 above 20,000 Feet will make its ability to stall higher as the thinner air and lack of prop thrust factors in.

Use the engine torque to cause the aircraft to spin to the right by backing off then throttling up.... all single engined prop jobs with a clockwise prop rotation will spin to the right easiler than to the left. Nose up and bank right with the rudder to the left and you should enter a flat spin. If the aircraft starts to rock from nose to tail you are in a "Falling Leaf Spin" which is not recoverable from, so your only option is to bail out.