It seems to be from the book 'Sled Driver' by Brian Shul [1] according to the following website [2], on which I found the same article of the parent link.

I'm a bit confused though, as I have read the part about the groundspeed check before, I found it again here [3]. This version is longer and worded more beautifully in my opinion. The poster below that is mentioning that it's from the same book so I'm a bit confused.

[1] https://galleryonepublishing.com/sleddriver/index.html [2] http://blogs.jobdig.com/wwds/2007/11/19/sr-71-now-that-was-s... [3] http://www.expressjetpilots.com/the-pipe/showthread.php?3197...