BarbiesBoyfriend:
They knew that they had to wait for their 550m.
They knew that they needed to hold until they got it.
Those are two profoundly fundamental and critical elements. But, there is a third equally important element: once commencing the approach (presumably with not less than RVR 550) they had to have an absolute discipline to not continue descent below the 200' DA unless one, or more of the required visual references were clearly visible and they were tracking centerline without any significant divergence, and their KIAS was stable and within specified value.
This is made significantly more difficult without a good, responsive flight director. During my past life we were not allowed to go below LOC-only MDA and associated visibility if both our flight directors were inoperative.