Why do helicopters deploy flares when taking off?

Generally, they only might do so if they're in an area where there's a real threat of their being attacked by an infrared guided surface to air missile. read more

Some military helicopters do this in a combat zone, only when there is a threat of infra-red homing missiles being used to shoot at them as they take off. Mostly these would be shoulder-launched surface to air missiles. read more

A flare or decoy flare is an aerial infrared countermeasure used by a plane or helicopter to counter an infrared homing surface-to-air missile or air-to-air missile. Flares are commonly composed of a pyrotechnic composition based on magnesium or another hot-burning metal, with burning temperature equal to or hotter than engine exhaust. The aim is to make the infrared-guided missile seek out the heat signature from the flare rather than the aircraft's engines. read more