When should exposure suits be present on the plane according to temperature?

Exposure suits are designed to protect pilots and crew from hypothermia in cold water scenarios. The correct choice indicates that exposure suits should be present when water temperature is below 50 degrees Fahrenheit. At this temperature, there is a significant risk of cold shock and hypothermia, which can occur quickly after immersion.

In cold water, the body loses heat much faster than in warmer conditions. The physiological response to cold water immersion includes gasping and hyperventilation, leading to potential drowning risks. Thus, the presence of exposure suits becomes critical for survival.

The other temperature options provided do not meet the critical thresholds where exposure suits are necessary. Water temperatures above 60 degrees are much safer for immersion, and temperatures at or above 70 degrees do not pose significant hypothermic risks. Therefore, ensuring exposure suits are onboard below 50 degrees provides essential protection for crew safety.