You may not descend below Decision Altitude (DA/DH) or Minimum Descent Altitude (MDA) unless ALL THREE of these conditions are met:
1. Aircraft Position (§91.175(c)(1))
The aircraft must be continuously in a position to make a normal descent and landing on the intended runway.
Must be able to land using normal maneuvers — no steep dives or abnormal configurations.
2. Flight Visibility (§91.175(c)(2))
The flight visibility (what you see out the window) must be at least equal to or greater than the visibility minimums prescribed for that approach.
This is pilot-observed visibility — not necessarily the reported visibility (though they should generally agree).
3. Visual References (§91.175(c)(3))
You must have one or more of the following distinct visual references for the intended runway clearly visible and identifiable to continue below DA/MDA:
Approach light system (ALS) — but only allows descent to 100 feet above TDZE, unless you see the red terminating bars or red side row bars (then you may continue to land).
Threshold
Threshold markings
Threshold lights
Runway end identifier lights (REILs)
Visual approach slope indicator (VASI/PAPI)
Touchdown zone or markings
Touchdown zone lights (TDZL)
Runway or runway markings
Runway lights
DA: Decision Altitude (precision approach)
The point at which you must decide to land or go missed on a precision approach.
MDA: Minimum Descent Altitude (non-precision approach)
The altitude at which you must level off at and reach the MAP (missed approach point) before going missed.