Where are buttock lines located when viewed from the top of the aircraft?

Buttock lines are reference lines used in aircraft design and construction to denote specific locations along the aircraft's width or lateral points when viewed from above. They typically run parallel to the aircraft's centerline and are crucial for ensuring symmetrical design and build quality.

When considering where buttock lines are located, they extend from the leading edges to the trailing edges of the aircraft and are particularly relevant to the fuselage's shape. In the context of viewing the aircraft from above, these lines are primarily associated with the fuselage structure rather than the wings or tail section. The wings and tail might have their own reference points for alignment and construction, but the buttock lines are specifically tied to the fuselage.

Thus, the correct answer highlights the relevance of the buttock lines to the fuselage, as they help in aligning the various components of the aircraft and ensuring that the fuselage design adheres to the intended specifications. This understanding is key in aircraft maintenance and is fundamental to ensuring the airworthiness of the aircraft.