What is the minimum required tread depth for a nose gear tire to be considered acceptable on an aircraft?

For a nose gear tire on an aircraft to be deemed acceptable, it is crucial that there are sufficient tread grooves present. In aviation, a tire's tread depth is vital for ensuring proper traction and preventing skidding during takeoff and landing, especially in wet conditions. Insufficient tread grooves indicate that the tire may not provide adequate grip or might fail to perform safely, which poses a significant risk during critical phases of flight.

While options about specific measurements of tread depth could relate to safety standards, the emphasis here is on the presence of tread itself. Having visible cords or treads that are less than the minimum required depth significantly reduces the tire's effectiveness and compromises safety. Thus, the standard for an aircraft tire, particularly for the nose gear, necessitates that there be suitable tread grooves, validating the choice of "insufficient tread grooves" as the correct answer.