Computer Simulation

In order to analyse the airframes and flight paths of the respective UA175 aircraft images I have utilised Microsoft's 'Flight Simulator 2004 - A Century of Flight' with the 'New York Objects' scenery kit that can be downloaded from

The 'New York Objects' scenery kit rebuilds the former World Trade Centre complex and together with the Project Opensky (POSKY) 767-200 aircraft model the simulated environment is complete.

I also used an International Flight Design Group (iFDG) 767-322 United Airlines aircraft model and an iFDG 767-200 American Airlines aircraft model to assist in the analysis.

The 'Flight Simulator 2004 - A Century of Flight' program ran on a Windows XP Operating System with the following hardware specifications: CPU - 1.56Ghz Athlon 1800 XP, Memory - DDR SDRAM 1GB, Graphics Card - Gforce 4 Ti 4200 128mb, Disk - 80GB Maxtor at 7200rpm with 8mb cache, Monitor - Sony Multiscan E250.

'Flight Simulator 2004 - A Century of Flight' features 'dynamic reflectivity' which means that compliant aircraft models can reproduce sunlight reflections from their airframes with a significant degree of accuracy.

Flight simulator does have some limitations. The most important one is that an aircraft models airframe will not cast a shadow over itself. To illustrate this point consider the graphic below which shows an approximation of the sun's orientation relative to the simulated UA175 aircraft on the morning of September 11th 2001:

Flight simulator is suggesting that the starboard engine nacelle is shadowing the area where the famous 'pod' is believed to have been located. We must bear in mind that the graphic above is only intended to give the viewer a rough idea of the sun's orientation when considering the points raised throughout this article. Where necessary, sun angles have been calculated with a higher degree of accuracy using NASA/JPL data shadows have been added to the images using Photoshop.

The graphic below shows the UA175 / WTC2 strike scenario from the suns point of view. This graphic gives us a good idea of how the airframe should have been illuminated by the sun, in terms of where shadows would have been falling and how bright or dark any given part of the airframe would have appeared to the ground positioned cameras.

For the purpose of this article we will consider the Boeing 767-200 in accordance with the 'official' version of events. I have superimposed the POSKY 767-200 on top of a photograph of a real Boeing 767-200 to show the reader how accurate the model is:

It's a close fit, the discrepancy in engine size could be down to a power-plant option chosen by the respective operators. It's difficult to differentiate between the real aircraft and the CG equivalent. Which one of the two United Airlines Boeing 767-200's below is real?

What must be noted is that the POSKY model has wings that are marginally longer than the real aircraft; and this will be factored into the analysis. It's a small point and even if we ignored it the outcome of the analysis would remain unchanged.

Next - How It Was Done