It's pretty difficult to use any kind of aircraft dynamics (whether a crash or a simple manoeuvre) to illustrate basic kinetics such as momentum, because the "laws" about conservation of momentum apply to a closed system, and an aircraft is an open system, with momentum being in effect continuously exchanged between the aircraft and the atmosphere.
So, for example, for entry into a spin (of the classical, training, type, not an accident) the aircraft would start by slowing down (by reducing engine power, so that the drag of the air slows the plane down). Then, at a low enough speed and high enough angle of attack you'd pull back on the stick (increasing angle of attack, more drag, slowing down faster) and kick the rudder to start the aircraft yawing. If it goes correctly the yawing motion and pitch up combine to create a rolling motion where one wing stalls more than the other, and you'll get a three axis rotation (pitch roll and yaw). Because the aircraft is now in a "disroganised" state aerodynamically, the drag will be huge and the plane will lose most if not all of its forward velocity. Its also not generating much lift, so will start to drop, and the motion will become a fairly steep descent. The aircraft will keep gyrating as it falls as long at the controls are positioned correctly, and the forces to keep it spinning against the natural drag of the air are extracted by means of lift generated on the different bits of the aircraft.
So it's not really a case of converting one form of momentum to another. Bear in mind too that the air around the aircraft is being disturbed too, and the whole closed system is conserving momentum.
Sorry if thats not very helpful or encouraging, but you've picked a pretty tough (though Ill agree interesting) way to illustrate mechanics.