Fears of attacks on aircraft, especially commercial aircraft, involving shoulder-launched missiles have increased since the terrorist attacks on American soil on Sep. 11, 2001.  Shoulder-launched missiles are no doubt in the hands of some of the world's most dangerous terrorist groups, such as Al Qaeda and Hezbollah. 
There are several types of shoulder-launched missiles.  All are about five feet long and weigh less than forty pounds, which makes them highly mobile.  The U.S.-made Stinger and Russian-made SA-7 Strela are the two most widely used types of shoulder-launched missiles by terrorists in attacks dating back to 1996.  Each has a range of over three miles and uses a heat-seeking infrared (IR) guidance system to hone in on targets.  In addition to their mobility and weight, these weapons are dangerous because they require very little training in order to operate. 
While small aircraft are vulnerable to MANPAD attacks, larger aircraft, such as commercial airliners, are at greater risk because they present a greater IR heat source for the incoming missile.  Additionally, current IR guided missile sensors have very narrow fields of view, and thus dispersed engines on a larger aircraft present several targets to the incoming missile.  Large aircraft are particularly vulnerable during takeoff and landing because they are lower to the ground, and when landing, are moving at a slower velocity. 
Current aircraft protection involves on-board countermeasures, such as pyrotechnic flares and on-board turret-based IR jammer systems.  Flares pose a high risk of fire to the surrounding areas, and during takeoff and landing, when the aircraft is most vulnerable, they lack the airspace needed to disperse and act as a decoy for the incoming missile.  On-board, turret-based IR jammer systems are very effective, since they would generally be in the field of view of the approaching target, but with each ship set cost ranging between one and two million dollars, outfitting all 6,800 commercial airliners to date would be a costly venture.