Why should a control surface be locked when an aircraft is parked?

Locking a control surface when an aircraft is parked is primarily done to prevent damage from wind. When parked in an exposed area, strong gusts of wind can cause control surfaces such as ailerons, rudders, and elevators to move uncontrollably. This movement can lead to structural damage or misalignment of the control surfaces, which can be expensive to repair and may compromise safety when the aircraft is next flown. Locking the control surfaces mitigates this risk by keeping them in a fixed position, ensuring that they do not flutter or move due to the force of the wind.

While safety during fueling, preventing movement due to weather conditions, and maintaining the correct aircraft position are important considerations, the primary reason for locking control surfaces is to specifically safeguard against damage caused by wind.