There are five things a pilot must remain aware of when contemplating aerial engagement; of these, seeing and keeping sight of one's opponent are the most important. In Southeast Asia, over 85 percent of all kills are attributed to the attacker spotting and shooting the defender without ever being seen. Structural limitations of the attacking and defending fighters must be taken into account, such as thrust-to-weight ratio, wing loading, and the "corner speed" (the maximum or minimum speed at which the aircraft can attain the best turning performance). Variable limitations must also be considered, such as turn radius, turn rate and the specific energy of the aircraft. Position of aircraft must quickly be assessed, including direction, angle off tail (the angle between flight paths), and closing speed. Also, the pilot must be aware of his wingman’s position and maintain good communication.