What type of instrument flight time can a second in command of a two-pilot aircraft log?

The second in command of a two-pilot aircraft can log all the time they are controlling the aircraft solely by reference to flight instruments. This is because the regulations allow a pilot to log instrument flight time when they are actively piloting the aircraft under instrument flight rules, which includes when they are navigating and controlling the aircraft solely using the instruments, regardless of whether they are the pilot in command.

When the second in command is at the controls in conditions requiring instrument flight, every minute during which they are flying the aircraft while receiving and interpreting data solely from the instruments qualifies as instrument flight time. This logging is significant for accumulating experience towards meeting eligibility requirements for instrument ratings and further advanced qualifications.

The other choices relate to logging practices that do not fully align with the regulations: for instance, logging only one-half the time on an IFR flight plan or in actual instrument conditions does not adequately reflect the comprehensive scope of flight activity that can be credited, as it fails to recognize all the time spent actively piloting the aircraft under instrument conditions.