I have about 700 hours in the MD520N. And about the only good thing about, it is safer on the ground (not in the air). It does not work well at altitude. Not stable in winds. Tail takes too much power...etc. Although the tail has the same authority as the MD500E, it reacts to inputs a lot slower. Just before going through transitional lift on landing, you need to pull a slight amount of collective in, and slight forward cyclic to stop the "ass tuck" it likes to do. You should see what the manuel says will happen if you have a tail problem (stuck thruster, pedal) get below 20kts, and you are not skidding on the ground.
Although I do not know what the winds were in Mexico, the MD600N has a critical wind azimuth in the limitation section that says that at high altitude and any weight, you can not have any wind on the right rear area. You can exceed the power limitations attempting to correct for the winds. That is a possibility of what may have happened.
Also, a lot of the police departments in the western U.S. are dumping their MD520's and MD600's they have. A fair amount of them are going back to MD500E's.