Which of the following is NOT a part of Visual Flight Rules (VFR)?

Flying at night without any instruments is not a part of Visual Flight Rules (VFR) because VFR guidelines primarily apply to operations conducted in clear conditions where pilots maintain visual reference to the ground and other landmarks. Under VFR, it is essential for pilots to have the appropriate visibility and weather conditions to avoid relying on instruments entirely. Additionally, VFR regulations often include specific requirements for visibility and cloud clearance, particularly when flying at night.

In contrast, the other aspects mentioned align with VFR principles. Maintaining visual contact with the aircraft ensures that pilots can constantly assess their position and surroundings. Weather minimums for visibility dictate the required conditions for safe VFR flight, ensuring pilots have adequate sightlines to navigate effectively. Using visual references to navigate is a fundamental component of VFR, as it emphasizes the pilot's ability to "see and avoid" obstacles and other air traffic.