I just discovered with the "AVIA 51/156" Tri-Motor, by milton Schupe listed on the front page.  Apparently it has a detailed virtual Passenger Cabin, tho the inside Views were NOT added to the Aircrafts CFG File, for simmers to be able to view the inside of the detailed passenger cabin and see out the windows while in flight etc. I'm going to try to post the View points that I used , for which I modified the "Aircraft CFG File", and I put these additional view's under the "General" area within the CFG file -(copy & paste) these views into your AVIA 51/156 aircraft/ CFG File and then "Save". Note: I have track IR-5, so I can look around from all angles, for those that "DON'T" have a head Tracking device- these may be a tad bit off, as far as the view point, but you'll still be inside the passenger cabin, just hit the "A" buttton on your keyboard to "cycle" thru all the views. Need any help just ask, or somebody will help you on here. thanks, the Jetranger.                                                                                                                                                                                                                                                                                                                                         [CameraDefinition.001]

                                 
Title = "passenger"
Guid = {0456199A-99D4-11DC-B263-66CC55D89593}
Origin = Virtual Cockpit
MomentumEffect = Yes
SnapPbhAdjust = Swivel
SnapPbhReturn = False
PanPbhAdjust = Swivel
PanPbhReturn = False
Track = None
ShowAxis = YES
AllowZoom = TRUE
InitialZoom = 0.48
SmoothZoomTime = 2.0
ZoomPanScalar = 1.0
ShowWeather = Yes
XyzAdjust = TRUE
ShowLensFlare=FALSE
Category = Cockpit
PitchPanRate=20
HeadingPanRate=60
InitialXyz=0.5, -0.09, -0.82
InitialPbh=13, 0, 68
[CameraDefinition.002]
Title = Passenger Seat Left
Guid = {D709A202-DA10-4095-AF83-D5E2A7001084}
Origin = Virtual Cockpit
MomentumEffect = Yes
SnapPbhAdjust = Swivel
SnapPbhReturn = False
PanPbhAdjust = Swivel
PanPbhReturn = False
Track = None
ShowAxis = YES
AllowZoom = TRUE
InitialZoom = 0.6
SmoothZoomTime = 2.0
ZoomPanScalar = 1.0
ShowWeather = Yes
XyzAdjust = TRUE
ShowLensFlare=FALSE
Category = Cockpit
PitchPanRate=20
HeadingPanRate=60
InitialXyz=-0.17, -0.50, -1.73
InitialPbh=6, 0, -55
[pitot_static]
vertical_speed_time_constant = 2
pitot_heat=1.000000                                                                                                                        

Jetranger, the reason why the AVIA doesn't have Viewpoints was because it was not designed for FSX it was designed for FS9; this is just a FSX port-over.

BTW you can move about in the Cabin by pressing Shift + Backspace, Shift + Enter, Ctrl + Backspace, Ctrl + Enter, Ctrl + Shift + Backspace & Ctrl + Shift + Enter.