What is the number of chains necessary for a heavy weather tie down?

For a heavy weather tie down, the standard practice requires the use of 20 chains. This number is based on ensuring that aircraft are securely anchored in conditions where wind and weather present significant challenges. The primary goal of using this number of chains is to maintain the structural integrity and safety of the aircraft by providing adequate resistance against strong winds, preventing movement, and minimizing the risk of damage.

In contrast, the other options represent inadequate or excessive numbers of chains for the requirements of a heavy weather tie down. Fewer than 20 would not provide the needed stability, while more than 20 could lead to unnecessary material use and logistical inefficiencies without offering additional safety benefits in this specific context.