Which flight time may be logged as instrument time when on an instrument flight plan?

The correct choice highlights that instrument time is logged only during the periods when the pilot is controlling the aircraft solely by reference to flight instruments. This means that the pilot must be actively relying on the instruments for navigation and control rather than outside visual references.

When flying under an instrument flight plan, a pilot may occasionally need to reference outside conditions, such as during takeoff or landing phases in certain circumstances, and this would not qualify as instrument time. The key point is that true instrument time reflects periods of flying where the pilot’s primary visual input comes from the aircraft's instruments, ensuring that they are practicing and demonstrating the skills required for instrument navigation and control.

Other options present misunderstandings about what constitutes instrument time. For example, simply being on an instrument flight plan or flying in IFR weather does not automatically qualify all logged time as instrument time. Similarly, being above the minimum safe altitude does not necessarily mean the pilot is operating solely by instruments. Thus, only logging the time when control is exclusively managed through instrument readings is the precise criterion for instrument time.