Which description best fits a scenario where the nose is down 45 degrees, banked 90 degrees, while flying towards the west?

The scenario described indicates that the aircraft's nose is positioned down at a 45-degree angle and banked at 90 degrees while flying west. This configuration strongly suggests that the aircraft is in a steep turn.

In a steep turn, the aircraft is intentionally banked significantly, often around or exceeding 30 degrees, to change direction while maintaining altitude or adjusting its flight path. The nose being pointed down implies that the aircraft is likely losing altitude as it turns. The combination of both a high bank angle and a nose-down attitude is characteristic of a maneuver where the pilot is maintaining control while executing a turn, which requires careful management of airspeed and altitude to avoid stalling during this aggressive maneuver.

Climbing to a higher altitude or preparing for landing would typically involve a nose-up attitude rather than a nose-down position and generally do not involve steep banking. Entering a stall condition would also usually be associated with a nose-up attitude as the aircraft approaches its critical angle of attack. Therefore, the depiction of the aircraft in a steep turn directly aligns with the conditions presented.