What should be visible on the main gear tire for an aircraft to be unacceptable for use?

For an aircraft tire to be deemed unacceptable for use, the visibility of cords is a critical safety concern. When tire cords are exposed, it indicates significant wear and degradation of the tire structure, which can compromise its integrity and performance during flight. The cords provide essential strength and support to the tire, and their exposure suggests that the tire has reached a dangerous level of wear.

In aviation, maintaining the tire’s condition is vital for safety, as tires are subjected to significant loads during takeoff and landing. Therefore, if cords are visible, it poses a risk of tire failure, which can lead to accidents or incidents during ground operations or while in the air.

Green cords and white threads are less definitive indicators of wear, as they may represent different tire designs or constructions that do not necessarily indicate failure. Black markings typically do not imply a problem either, as these could be part of the tire's manufacturing process or tread design. Thus, the visibility of cords directly relates to the structural integrity and overall safety of the aircraft tire.