Before you try messing with the model itself there's another possible problem and solution that could be causing it... if the content creator forgot to turn "bending" off on the parts of the helicopter when it was set up then this will happen (i've had that with my own models when I forget to turn bending off in them)...

Try loading the item, select all of it's various bones in your scene tree and in the properties menu simply turn "bending" option off (on mechanical devices for the most part bending doesn't need to be on)... this may be the source of the issue and takes about 30 seconds to fix without risking changes to the object file...

If turning the bending off doesn't fix it then go with the above suggestions... :)