Final answer:
An aircraft is restricted from running its engine against the gust lock because of design limitations to prevent potential damage to the control surfaces and ensure the aircraft's structural integrity and safety.
Step-by-step explanation:
Due to design limitations of the aircraft, the aircraft is restricted from running the engine against the gust lock when the rotor brake gust lock engagement lever is installed. This is an important safety measure to ensure that the aircraft's control surfaces are not inadvertently damaged by applying engine power while the controls are immobilized by the gust lock. In aviation, the gust lock system is used to prevent the aircraft's control surfaces from moving and potentially being damaged when the aircraft is parked and subjected to strong winds.
The gust lock engagement lever is part of the aircraft's safety mechanisms that physically restrict movement of the control surfaces. This lever should be disengaged before the aircraft's engines are started to avoid stress or damage to the locked control surfaces. Operating an engine with the gust lock in place could lead to unwanted torque and force being applied to these surfaces, possibly resulting in damage to the aircraft's structural integrity. Therefore, it is essential for the proper operation of the aircraft to recognize and comply with this design limitation.