In IFR flight, what is the rule for maintaining aircraft separation during an approach?

In IFR flight, maintaining aircraft separation during an approach is primarily governed by following Air Traffic Control (ATC) instructions for vertical and lateral separation. This means that pilots must adhere to the directives issued by ATC, which are designed to ensure a safe distance between aircraft at all times, particularly during the critical phases of flight such as approach and landing.

ATC provides clearances that outline the required altitude and spacing between aircraft, taking into account current traffic, weather conditions, and any other relevant factors. By following these instructions, pilots help to prevent collisions and promote smooth traffic flow in controlled airspace.

The other options do not accurately reflect the regulations governing IFR flight. For instance, maintaining VFR visibility requirements is not applicable in IFR conditions, where visibility may be below VFR minimums. Using onboard separation equipment is helpful, but it does not supersede ATC instructions. Performing constant altitude changes may not be necessary or safe and could disrupt the established separation requirements as determined by ATC. Therefore, adherence to ATC guidance is the most critical and effective method for maintaining separation during an approach in IFR conditions.