Current missile-warning sensors on aircraft mostly operate in the ultraviolet wavelength band. Aimed primarily at detecting short-range, shoulder-fired surface-to-air missiles, the detection range of the sensors is of the same order as the threat range, which is 3-5 km. However, this range is only attained against older missiles, with bright exhaust flames. Modern missile developments include the use of new propellants, which generate low-intensity plumes. These threats are detected at much shorter ranges by current ultraviolet warning sensors, resulting in short reaction times. Infrared sensors are able to detect targets at a much longer range. In contrast with the ultraviolet band, in which a target is observed against an almost zero background, infrared sensors must extract targets from a complex background. This leads to a much higher false-alarm rate, which has thus far prevented the deployment of infrared sensors in a missile warning system. One way of reducing false-alarms levels is to make use of the spectral difference between missile plumes and the background. By carefully choosing two wavelength bands, the contrast between missile plume and background can be maximised. This paper presents a method to search for the best possible combination of two bands in the mid-wave infrared, that leads to the longest detection ranges and that works for a wide range of missile propellants. Detection ranges predicted in the infrared will be compared with those obtained in the ultraviolet, to demonstrate the increased range and, therefore, the increased reaction time for the aircraft.