I should add (hence the edit) the due to the potentially bogus guidance that the Flight Director system can give you, i.e. when descending below the MDA on a non-precision approach, it is customary (and good practice) on the B737 - once you are visual with the runway (and certainly if continuing below the MDA) - to turn both Flight Directors briefly off and then on again. The causes the Flight Directors to disappear out of view for the remainder of the approach to the runway (i.e. you continue the landing entirely 'visually'), however, should you press the TOGA button, the Flight Directors will then reappear to provide go-around guidance. This is typically known as 'Flight Director Pop-Up Mode'
OKC,
I found this part of your post fascinating. I've spent the last eight years in the left seat of the NG and have never heard of this procedure. Its not in our procedures.
On an IAN approach the FDs will guide you down to 50 feet above the runway. However, it's not good practice to rely on them since you are below MDA. PAPI, VASI or visual reference are the approved guidance below MDA. Our book does allow us to "observe" the FD guidance below MDA in conjunction with visual references. It will provide accurate guidance with one caveat; a difference in actual airfield QNH/Temp and VNAV Baro, may cause a difference between VGSI and the GP indication.
Interesting stuff. Excuse the thread drift.