Some meshes use large scale models.
This can be confusing, as it does seem counter-intuitive. DOWN arrow moves the viewpoint backwards towards Negative X-Axis values. PAGE UP key moves toward more Positive Y-Axis values, so you can use this to look down from a height above the main hull of the ship. PAGE DOWN moves further down the Negative Y-Axis, so the viewpoint looks up from underneath. LEFT key increases the Negative Z-Axis values.