Scene is divided into six layers. Default Layer is empty. Scene layer, now hidden, contains one object - 'B737_PROXY'. This is low detail model of airplane and it's at the top of the hierarchy - all the objects are connected to it. So it's supposed to be used for transforming (moving, rotating, scaling) whole plane and also for animating - it's really lowpoly so it's not decreasing performance.
You can see what is in the other layers from their's names, or by hiding them.
In Select Objects (Select by name) dialog with 'Display Subtree' turned on, you can see there is pretty well built hierarychy - at the top there is 'B737_fuselage', connected to that 'PROXY', as I mentioned before. Everything is connected thoughtfully.
Also take a look at the names of the objects. Everything begins with 'B737_', which is very useful! Each part is named rationally, so orientation in the scene is easy.
For example, you want to select whole one window (outer and inner casing, glass) - you just simply use 'Display Subtree' and 'Select Subtree' features in Select Objects dialog. And if you want to select, for example, all the inner window casings, just turn 'Display and Select Subtree' off and select all the inner casings - because of naming, they're all together in the list.
Instancing or referencing objects is used a lot - which makes editing mesh and modifiers of all the 72 windows very simple! Of course, symmetrical parts (engines, wings...) are instanced too.
All the objects are Editable Poly, most of them with TurboSmooth/MeshSmooth modifier on top. You can adjust number of display/render iterations to find the balance between performance and smoothness. All these MeshSmooth/Turbosmooth modifiers have 'Isoline Dispaly' turned on.
There are also UVW mapping and/or UnwrapUVW modifiers on most of the objects. Sometimes there are more than one mapping modifiers with different map channels - because of very complex layered maps in some materials. These modifiers are named according to their map channel. Some objects also uses FFD and/or Symmetry modifiers.
Pivots of all parts are set well so you can rotate moving parts with no problem. Using Angle Snap 5 degrees provides you best way to close the landing gear door etc.
MATERIALS AND MAPS
Most of the objects use their own material with own maps. All the materials are Standard, all the maps are bitmaps (no procedurals) and reflection is achieved with Raytrace maps. Most of the materials have diffuse maps, some of them have also bump, specular, opacity and refelction maps. All the bitmaps are jpgs. In many materials, there are really complex maps - composites, mix, masks... Structure of maps in each material can't be explained here, you must really go deep into it. Some examples of maps structures are shown in thumbnail pictures. Incredible detail on some parts of the airplane is achieved with mixing many bitmaps with different map channels using composites and masks. This also allows you changing for example the main colour of the airplane or density of rust, dirt and scratches etc, just by changing Output Amount of masks, you can also change the texts etc... Bitmaps were composed in Photoshop using photos, free texture libraries, painting and baked ambient occlusion maps.
See included readme for more info.