The most dangerous anti-aircraft weapon in Afghanistan is not 15 year old US Stinger missiles, but RPG rockets and rifle fire. The Stinger's still in Afghanistan won't work because their custom batteries have long since died. More recent portable Russian anti-aircraft missiles are not effective against low flying U.S. helicopters (the only American aircraft likely to be in range) because these aircraft have defensive systems that easily defeat missiles (using flares and missile detectors.) There is no defense against the RPG rockets. Of course, the RPGs only work if many (over a dozen, if possible) are fired at a chopper from close range (a hundred or so meters away.) These conditions are rare, but they do occur, and helicopters have been brought down by RPGs. Rifle fire, particularly from larger caliber machine-gun (14.5mm and larger), have also brought down choppers, although more commonly the result is just a lot of damage. But all that damage often leads to a helicopter being forced down in enemy territory. Not a pleasant prospect.