What distinguishes main deck loading from lower deck loading?

Main deck loading is designed to accommodate larger cargo and equipment because it offers more accessible space, allowing for the handling of oversized or bulky items. This is a significant feature that distinguishes it from lower deck loading, which is generally intended for smaller items, often packed in containers or pallets that are not as large or cumbersome.

The distinction is largely due to the design and structure of the aircraft. The main deck is spacious and can handle larger unit loads, whereas the lower deck has limitations in height and width, necessitating the use of smaller containers or packages. This makes option B the correct choice, as it accurately reflects the characteristics of both loading areas.

The other choices present concepts that do not align with standard practices in air cargo operations. For instance, while fragile and heavy items are placed in specific areas for safety, the general categorization of payload based on fragility or perishability does not accurately define the primary differentiator between the main and lower deck. Similarly, the timing of loading, whether at night or during the day, does not inherently dictate the type of cargo that is loaded into either compartment.