Alexander Smirnov, the designer of the Russian Igla (SA-18) portable surface-to-air missile, insists that his creation cannot take down large commercial aircraft. Experience with missiles like the SA-18 against large military and commercial aircraft seems to confirm this. The missiles are used at low altitude, so the warhead fragments cannot cause explosive decompression of an aircraft. This is what has brought down commercial aircraft when smaller amounts of explosives were used in terrorist bombs. Missiles like the Igla have warheads with about two pounds of explosives, and several more pounds of metal fragments. Last year, Russian troops captured six Igla missiles from Chechen rebels, who had bought them illegally from Russian troops, or thieves who had stolen them from Russian arsenals. At least one, and maybe two, Russian helicopters have been shot down in Chechnya with Igla missiles. Others have been brought down using older Russian missiles. Helicopters are the most common military targets for missiles like the Igla. Helicopters are more vulnerable than fixed wing aircraft, because they often have only one engine, or two that are set close together. Fixed wing warplanes usually don't fly low enough to be hit by these small missiles, and those that do come in low, like the A-10 or Russian Su-25, are designed to take a hit from something like an Igla and survive (although with a lot of damage.)