How is an inappropriate altitude/flight level for direction of flight recorded on the flight progress strip?

The recording of an inappropriate altitude or flight level for the direction of flight by underlining it in red serves as a visual cue to alert air traffic controllers to the discrepancy. This method effectively draws attention to the fact that the assigned altitude does not comply with the expected standards for the aircraft's flight direction. Underlining in red is a widely recognized practice in aviation communications that helps maintain safety by making it clear that an altitude change is needed or that there is a potential issue that requires further action.

The other options, while they suggest different methods of notation, do not carry the same level of standardization or clarity as underlining in red. For instance, writing in italics may not be conspicuous enough to alert controllers of an issue effectively, while boxing an altitude in red might imply it is valid but needs further emphasis rather than indicating a problem. Crossing out the altitude could lead to confusion, as it might suggest that the information is no longer relevant or should be disregarded entirely. Thus, underlining in red stands out as the most effective and established method for signaling a discrepancy in altitude.