Don't use the viewports to display any background, as well as 3-view images. Your best bet is to crop the images into separate parts and apply each part as a texture to a plane [primitive object]. Example: one plane has a left view of the aircraft image applied to it as a texture and vise versa.

There is also a way to reduce the ratty effects of the textures within Gmax [took me a while to figure it out]. Go to Customize > Preferences > Viewports > Configure Drivers > Select 512 > Check "Match bitmap size as close as possible". From there, the applied textures will appear more clearly than before. Believe me, it helps a lot. Especially if you want to keep an eye on tiny details within the interior.