Better method for part copies than Mirroring
Mirroring
So there has been a long standing problem with inverted pivots in 3ds Max. That is that when mirroring a part, such as a wing for instance, the pivot will also be mirrored. You can most times solve this by going to the Hierarchy tab and turning on "affect pivot only" and then clicking "align to world". Sometimes however the pivot will not obey this as I recently encountered as I have many times before. The old work around was to create a new simple object, convert it to a poly then attach the offending part to the new object. This will now give the new pivot to our object at the new objects center. We can then use the "element" sub-selection to pick the new part and delete. Then "affect pivot only" and finally "center to object".
Symmetry
An alternate way of making a mirrored copy of an object and that is the "Symmetry" modifier. The method is as follows: Using a wing for example. Select the wing then select "Symmetry" in the modifier drop down. Select the X axis radio button. Then expand the modifier in the stack and select the mirror then with the move tool active right click on the up and down arrows next to the x coordinates box at the bottom of the window to set it to zero.
Now you will have both wings that are part of the same object. Select the element sub selection and click the new wing and detach. Selecting the new wing will show that the pivot is still at the original wings pivot so now we just go back to the hierarchy tab and select "Affect pivot only then "Center to Object".
Symmetry works reliably because it does not mirror the pivot.