Which of the following is not a wind speed category mentioned for tie down?

The correct choice indicates that "Severe weather tie down" is not a wind speed category mentioned for tie down procedures. In aviation, tie down procedures are critical for ensuring that aircraft remain secure in various weather conditions, and they are categorized based on specific wind speeds that the aircraft can safely withstand.

The wind speed categories typically used include "Initial tie down," which pertains to the basic level of securing an aircraft, "Heavy weather tie down," which applies to situations with substantial wind gusts, and "Normal weather tie down," which refers to standard conditions without significant wind. Each of these categories provides guidance on how to properly secure an aircraft against expected weather conditions.

In contrast, the phrase "Severe weather tie down" does not correspond to an officially recognized wind speed category in the context of tie down procedures. Understanding these categories helps in ensuring proper safety measures are in place to protect the aircraft from damage due to wind and other environmental factors.