I have a trainer with an OS40LA which until now has run without any problems. However just recently I have noticed that the motor will often stall briefly during flight and then pick up revs again. It does this for no apparent reason so I cannot put it down to anything in particular. The other day it did it on every flight I had except the engine stalled and died so I ended up doing my fist of 5 dead stick landings. The engine runs fine whilst the plane is on the ground though.

Any ideas??

Troy.