[Oorang]

Well since what my friend told me contradicts what BearWash said, I'll just leave it with "Heck, I don't know"!

[steve86]

We're really both right. An aircraft flying a "normal" course and altitude will almost always show up on radar over developed or semi-developed areas. But just like in military operations, and I assume terrorists know this, there are ways to evade the coverage.