During an IFR approach, if an aircraft cannot maintain the required altitude, what should the pilot do?

Notifying Air Traffic Control (ATC) immediately is the appropriate response when an aircraft cannot maintain the required altitude during an IFR approach. This action is crucial for several reasons.

First, ATC is responsible for ensuring the safety of all aircraft within their airspace. By informing them of the inability to maintain altitude, the pilot provides ATC with essential information that can affect the traffic flow and safety of other flights. This allows ATC to make necessary adjustments, such as altering the aircraft's course or altitude to prevent potential conflicts with other aircraft.

Second, maintaining proper communication during IFR operations is critical for safety. Pilots are trained to prioritize communication with ATC in situations where their aircraft's performance is compromised. This helps ensure that all parties are aware of the situation, facilitating timely and appropriate responses.

The other choices involve actions that could potentially compromise safety. Descending to the minimum safe altitude without ATC guidance may lead to unsafe flight conditions, and attempting to regain altitude might not be feasible depending on the circumstances. Continuing the approach without clearance could result in an undesirable or dangerous situation. Thus, contacting ATC is the most responsible and safe course of action.