Aircraft have to tied down to the deck when not in use and during maintenance evolutions. The wind velocity determines which category of tie-down must be used for securing the aircraft. The categories are:
- Up to 45 Knots. Initial tie-down: a minimum of 6 chains are required, initial tie-down is used immediately prior to, in between, or immediately after flight.
- Up to 45 Knots. Normal weather tie-down, 9 chains required.
- 46 to 60 Knots. Moderate weather tie-down, 14 Chains required.
- Above 60 Knots. Heavy weather tie-down, 20 Chains required.