I'm curious, but doesn't the altitude play a role for GS?
Not for the calculation of TAS/IAS etc, but rather due to the fact that if you are high above a surface and flying along a curved surface (ie the earth), then the distance you cover at a high altitude is longer than the distance you would cover on the surface if you were directly over it.
I wonder if the 35000 ft or whatever you were at play a role in this equation?
Also, I wonder if´the IRU's make any consideration of this? I assume an IRS would bascially compute the location "at altitude", rather than the true position you would be at on the surface, but a GPS could calculate your "true" position.
I hope any of this makes sense?
Regards,
Mark