Some explanation of how LTE occurs:
1) Every tail rotor has minor variations in its thrust output, based on the precise flow it is experiencing. If you put some turbulence into a rotor, the thrust will drop a bit. I have experienced this thrust change in every helicopter I have flown.
2) When you are operating at peak thrust, (max pedal angle) there is no more yaw control available. Should any turbulent flow enter the tail rotor, there is no more thrust available.
3) Main rotor torque is big, tail rotor thrust is small. A 5% increase in main torque can completely swamp a tail rotor that is at maximum thrust, and therefore at its control margin. A 2% increase in main torque beyond maximum yaw control will look like a wild ride, with the tail whipping around.
4) Most helicopters have excess tail rotor thrust, so that small thrust changes do not unleash the beast. A tail rotor that is very marginal will experience the same slight loss of thrust, but is more likely to experience LTE because it is riding on the edge and has little to help recover.
5) Sometimes the main rotor wake slips into the tail rotor, it can be heard and felt, and it can cause a 5% loss in tail thrust. That is why the azimuth diagram exists on the Advisory Circular, to help show where this occurs.
6) If the helo has little extra tail rotor thrust and collective is misused slightly at the bottom of an approach, so that the torque is somewhat above hover torque at the bottom, LTE can occur. The best way to make LTE occur is to make the approach too fast, so that you make a quick stop at the bottom, and suck in a lot of collective to stop the descent. That is precisely where most LTE's occur.
LTE occurs when a marginal helicopter runs out of yaw control while inside its envelope, LTA occurs when a proper helicopter is pushed outside its envelope. Both have run out of yaw control, but the LTE bird is in far worse shape, because there is nowhere to fix it. The LTA bird asks that we lower the collective, stop pulling too much power (stop climbing, usually) reduce the engine power, and all gets right.