Final answer:
A PIC must not begin an IAP with visibility less than 3/4sm or RVR 4000 unless specified by the procedure or authorized by ATC, often in the context of practice approaches or for certain lower-visibility CAT II/III approaches with proper equipment, training, and clearance.
Step-by-step explanation:
A Pilot in Command (PIC) shall not begin an Instrument Approach Procedure (IAP) when the visibility is less than 3/4 statute miles (sm) or Runway Visual Range (RVR) 4000 unless there is a requirement in the approach procedure itself or when authorized by Air Traffic Control (ATC) for the purpose of conducting a practice approach. This exception would typically be noted in the approach chart's minimums section or be communicated by ATC during flight operations.
One example when this rule may be waived is for certain Category II or Category III approaches, which are designed to allow landings with visibility values lower than the standard minimums. However, specific equipment, crew training, and operational approvals are required for these types of approaches. It is vital that pilots adhere to the established minimum visibility requirements for safety unless specific exceptions apply.