Its rare because in virtually all light aircraft the flaps are controlled off a straight rod which links both flaps to one point of control.
That point of control is on purpose designed to be the weakest link. So if there are any jams etc it will sheer leaving both flaps in a fail safe symetrical condition. In most cases the flight loads will run them to zero. I have had this when a pin sheared in a PA28 a big bang and all the flap went. And the reason it went was because 3 known dicks used to regularly stick the flaps out above the flap speed cause some spanish prat of an instructor told them it didn't do any harm. And they liked getting the leans when they did it.
The next point of failure are the rods which actually push the flap out and down. These should be checked on every pre flight and are checked and greased by the engineers every 50 hours. All wire locked and split pinned.
The next failure point is the guides and hinges again these are checked every 50 hours and all are wire locked and split pinned. Every so often as per the engineering schedual they are dye pen'd NDT for cracks.
Then there is the rod which is graded metal and if that goes I suspect your wings have come off cause the only way that will break is due to fatigue or corrosion issues and if it is in that bad nick I would hate to imagine what the main spar is like, and you have more problems than what your flaps are at.
Putting flaps out in a turn is not an issue its just folk law as FOK states.
If your student has been taught to fly by attitude the issues with airspeed etc are not a factor cause if they fly the attitude and set the power all they have to do is trim out the forces. And as been discussed on the other threads to do with approach speeds the attitude that will be required to stall the thing is that hurrendous they won't get to that stage. If you are at circuit speed and power setting and pull the whole lot of flap in one go with no control input you will not stall. The nose will go up the airspeed will go down the nose will drop and the aircraft will naturally come back to an airspeed which will be above stall and a decent rate. You will of course be totally off profile.
Last edited by mad_jock; 4th Apr 2010 at 10:59.