What is the purpose of active clearance control mechanisms in some engines?

• A. To adjust blade tips during operation to maintain clearance
• B. To cool the engine oil
• C. To measure fuel flow
• D. To monitor exhaust temperature

Answer: (A)

Active clearance control keeps the space between the blade tips and the engine casing at a precise, small value during operation. As the engine heats up, different parts expand at different rates, so clearances can change with temperature and load. ACC uses actuators to move the turbine case or shrouds in or out to compensate, maintaining the optimal tip clearance. This reduces tip leakage, improves efficiency, and lowers the risk of rubbing or blade damage during transients. The other functions listed aren’t what ACC does—they’re not about cooling oil, measuring fuel flow, or monitoring exhaust temperature.