Under what conditions does the gear handle light illuminate red?

The gear handle light illuminating red is an important safety feature that indicates a potential issue with the landing gear system. When the main gear inboard doors are not closed, it signifies that the landing gear may not be secured in its proper position. This condition is critical for the safe operation of the aircraft, as having the gear doors open while in flight can lead to drag and affect the aircraft's performance.

In contrast, the other scenarios involve different operational parameters. For example, if the power control lever (PCL) is approaching IDLE with the gear handle UP, it indicates a different mode of operation but does not necessarily mean there is an issue with the landing gear position. Similarly, when the landing gear is not fully deployed, while it may indicate a similar concern as when the inboard doors are open, the red illumination is specifically tied to the doors. Lastly, being in a steep climb does not directly relate to the condition of the gear handle light and does not trigger a red indication. Therefore, the situation of the main gear inboard doors not being closed accurately explains why the light would illuminate red.