Well I just finished both of Brown's famous controversial books:
The Da Vinci Code
Angels & Demons
This guy is a novelist, not an historian. I especially ran across it in certain elements on Angels & Demons. This guy, maybe doing a little research, didn't do enough. On page 5, I discovered discrepancies! I have a slight bit of knowledge that, when used, easily refutes what he used about hypersonic (above Mach 5) jets. The X-33 was a research vehicle that was supposed to be a RLV, or Reusible-Launch-Vehicle. Not like the shuttles of today, but more like an airliner, a space-liner, if you will. There were numerous problems with the X-33 R&D, and the project was cancelled in 2001. There even is a conspiracy theory surrounding the whole project. As of now, fastest air-breathing manned vehicle is the SR-71 Blackbird, traveling at speeds of up to Mach 3.3. The fastest air-breathing unmanned vehicle was the X-43a, reaching speeds of Mach 9.8, so speeds of Mach 15 (as mentioned in the book) by any manned vehicle are a definite problem.
I'm still reading the "Secrets of" series for both books, and its interesting, they pretty much call Brown's bluff and obliterate his "this is entirely factual" references.
you should check them out yourself.