The power source of air whistle is the compressed air. The whistle combines with pronouncing body, control valve, magnetic valve and thermal device complete. It can be whistled by manners of magnetic valve or manual pull rope. Please see Fig about the construction of WD-2A . The thermal device complete is applicable for navigation at icing period, which is controlled by the heating switch. When the power is switched on, the body temperature of whistle is always kept above 0℃, in order to prevent for icing up at low temperature, which maybe affect the sound quality.