Call Sign Similarity Rules

The use of similar call signs by aircraft operating in the same area on the same radio frequency is referred to as 'call sign similarity' (CSS). The danger of a pilot taking and acting on a clearance intended for another aircraft due to this phenomenon is a common occurrence and can lead to flight safety incidents.

The following similarity rules are recommended by the CSS User Group. The order within the following table is significant with the most critical rules at the top.