In principle, the infrared seeker obtains guidance information by detecting the infrared radiation of the target engine nozzle, tail flame and skin aerodynamic heating. Its operating range is not only related to the infrared radiation intensity and radiation spectral characteristics of the target, but also related to the sensitivity of the seeker and the meteorological conditions of the external environment. Among them, the most important factors affecting the action distance of infrared seeker are the exhaust temperature of engine tailpipe (nozzle) and the tail flame formed after the exhaust leaves the tailpipe. The influence of engine tail pipe is more obvious than that of tail flame.

The reason for this conclusion is that the tailpipe made of metal material not only radiates high infrared intensity, but also has a long duration of high temperature: under the condition of opening the afterburner, the length of the engine's tail flame can reach 200m, but in fact, the temperature of the tail flame after 30m drops to 100 ℃, so the part causing strong infrared radiation is only about 10-20m. In contrast, the exhaust flame can be easily cooled. As long as the thrust is reduced or cold air is introduced, the engine exhaust temperature can be reduced, and then the exhaust flame temperature can be reduced rapidly.

Generally speaking, the detection distance of the infrared seeker is approximately proportional to the square of the temperature of the tail nozzle of the target engine, that is, if the temperature of the tail nozzle is increased by twice, the detection distance of the seeker will be increased by four times. When a typical turbojet engine is at the maximum afterthrust, the detection distance of the infrared seeker is 5 times that of the engine in cruise; For turbofan engines, this gap will even reach 10 times. From this point of view, how dangerous it is for the tail of a jet fighter to be bitten by the enemy.
In order to survive in close combat air combat, the fighter's mobility is increasing. It is becoming more and more difficult to bite the tail of the enemy aircraft to attack. Therefore, short-range Infrared Air-to-Air Missiles often emphasize "omni-directional attack", especially head-on attack. At this time, the detection distance of the seeker will be greatly reduced, and the effective distance is not as good as 20% of the rear. The existing infrared seeker with 3 to 5 micron wavelength based on indium antimonide also forms a restricted area in front of the target because the infrared radiation intensity is too low, and the infrared missile can not capture the target at all in this area. However, the new short-range combat air-to-air missile is also changing the coverage band of the seeker, and its ability to capture targets has been further improved.