Definition
A federal aviation regulation that establishes the conditions under which a pilot operating an instrument approach may descend below the Decision Altitude (DA), Decision Height (DH), or Minimum Descent Altitude (MDA). Descent below these minimums is permitted only when three conditions are met simultaneously: (1) the aircraft is continuously in a position from which a normal descent to landing on the intended runway can be made using normal maneuvers and a normal rate of descent, (2) the flight visibility is not less than the visibility prescribed in the instrument approach procedure being used, and (3) at least one specified visual reference for the intended runway is distinctly visible and identifiable to the pilot (such as the approach light system, threshold, runway markings, runway lights, touchdown zone, or REIL).
Plain English
This rule says: at the bottom of an instrument approach, you can only go lower than the published minimums if you are lined up to land normally, you can see far enough by the published visibility, and you can clearly see at least one approved part of the runway environment.
Context Anchor
You will see this rule in instrument approach and missed approach discussions, especially when deciding whether to land or start the missed approach at minimums.
Derivation
14 CFR means Title 14 of the Code of Federal Regulations, the part of U.S. law that covers aviation. Part 91 contains general operating and flight rules. Section 91.175 is the specific rule for takeoff and landing under instrument flight rules, and subsection (c) is the part that controls descent below approach minimums.
Why Pilots Care
Determines the legal and safety point at which a pilot must commit to landing or execute the missed approach, directly affecting go/no-go decisions in low visibility.
Grounding Statement
At the bottom of an instrument approach, this rule answers the question: “Do I have enough real-world visual information to keep going down and land?”
Intuition Check
Do not read this as just a citation in a book. It points to a legal rule that controls the land-or-miss decision on an instrument approach.
Example Sentence 1
Reaching DA with only the approach lights in sight, the pilot applied 91.175(c) and continued descent to 100 feet above touchdown zone elevation, looking for the red terminating bars.
Example Sentence 2
When the runway environment was not in sight at the missed approach point, 14 CFR Part 91 § 91.175c required immediate execution of the published missed approach procedure.