[Greysard]

You can calculate the distance to the airplane if you can estimate the period of observation and the angle. The angle cannot be wider than the window, of course. You know the speed already. The length of the airplane is insignificant. (v*t)/2 = D*sin(α/2)

For example, if you observed the airplane for 1 second, and your view was 60 degrees, the minimum distance to the airplane was 0.333 miles, or 1758 feet.

[rlmorel]

The other plane filled between half and 2/3 of the horizontal window in the instant it flashed by.

It just seemed darn close to me, though I suppose there is no way the crew could have not seen it.