Intelligence agencies say Al Qaeda already has dozens of missiles, many of them American-made Stingers left over from the war in Afghanistan in the 1980's when the United States supplied them to Afghan guerrillas seeking to oust Soviet troops from their country. Hundreds of other surface-to-air missiles are reported to be circulating on the black market.That's true, but it's not the whole story. Stinger missiles do have a pretty long shelf-life, but the ones we gave to the muhajadeen in Afghanistan are more than 20 years old. According to what I've read in various places, most of these old missiles won't work properly.
More importantly, the consumables in the Stinger system degrade over time. Those given to the mujahedin were transferred in 1981, making them twenty years old. Batteries for electronics and liquified gases for coolant both will escape or run flat. While batteries might be easily replaced, the act of doing so will involve 'unsealing' a missile round, modifying it, and repackaging it. While this is not impossible, it is not easily accomplished either; at least, not in such a way that the user can be relatively sure the missile will function. IR seekers are extremely sensitive to damage, contaminants, and other environmental hazards.Which isn't to say that they aren't a threat at all, but we should be careful not to overstate it.
Naturally, Strategy Page has much more about knocking down airliners.
Larger airliners, like the Airbus's, and 757s, 767s and 747s, have not been brought down because these missiles were not designed to take on aircraft with such large and powerful engines. While these missiles were originally intended for use against jet fighters operating over the battlefield, the reality turned out to be different. The most likely targets encountered were helicopters, or propeller driven transports. These aircraft proved to be just the sort of thing twenty pound missiles with 2-3 pound warheads could destroy. Against jet fighters with powerful engines, the missiles caused some damage to the tailpipe, but usually failed to bring down the jet. This was first noted during the 1973 Arab-Israeli war, where the Egyptians fired hundreds of SA-7s at Israeli A-4 light bombers. Most of the A-4s, with their 11,187 pounds of thrust engines, survived the encounter. Larger jets, like the F-4 and it's 17,000 pound thrust engines, were even more difficult to bring down. Smaller commercial jets, like the 737 or DC-9 (each using two 14,000 pounds of thrust engines) have proved vulnerable. But a 757 has much larger engines with 43,000 pounds of thrust, and the 747 is 63,000. Moreover, the rear end of jet engines are built to take a lot of punishment from all that hot exhaust spewing out. Put a bird into the front of the engine and you can do some real damage. But these missiles home in on heat, and all of that is at the rear end of the engine. ...There's more, look for the August 14, 2003, entry. Hey Jim, get some permalinks.
They won't be using any of the Stingers the U.S. gave out in Afghanistan during the 1980s. The custom battery packs in those missiles gave out in the 1990s. It's a lot easier to get Russian missiles, and fresh batteries for them.