Some SA-7 anti-aircraft missiles were built for self-activated firing

The media are reporting that the Bush administration believes that al Qaeda may have smuggled SA-7 and/or Stinger anti-aircraft missiles into the US, although the White House says there is "no evidence" that such missiles are actually within our borders.

(So why the alert?)

The SA-7 Strela-2 (NATO nickname, Grail) is a first-generation Soviet-era missile, a blatant copy of the American Redeye, which was replaced by the Stinger. The Grail was not terribly effective against American aircraft in Vietnam. It has a small bursting charge of RDX/AP explosive; it was not unusual for single-engine fighters to survive a Grail hit and fly home. SA-7s home in on the engine heat of airplanes, but the Grail's seeker system was crude. A Phantom pilot I knew told me he threw several off track by flying straight toward the sun. Once the track is lost, SA-7s don't easily re-acquire. They can only acquire a target from the rear. They have a range of about 4.7 kilometers (about three miles).

I think a large airliner (B-737 or larger) could withstand a hit by a SA-7. Not that it would be fun, but probably the worst that would happen would be the loss of an engine, a problem for which airline pilots are well trained. Because the Grail is short range, an airliner would be close to an airport (taking off or landing) when hit. Onboard fire-control systems would hopefully manage the engine fire until the landing.

The Soviets developed a special version of the Sa-7 for use by the special operations forces, the spetznaz. It was called the Strela-Blok. It was an automatic missile, designed to be emplaced before hostilities near an enemy (i.e., NATO) air base. A timer would be set for it to become "active." Afterward, a directional microphone, aimed at the air base, would detect the sound of aircraft engines. The mike was linked to a frequency filter, a Doppler sensor. The Doppler sensor was connected to the firing mechanism through the power module.

Usually, the mike was designed to aimed at the end of the runway, at a 45-degree angle upward. It would detect all aircraft noise from ground level to 12 degrees past vertical in the sky.

When an aircraft passed overhead, the Doppler sensor would compute when the Doppler curve began to decrease, indicating that the closest approach had just been passed. It would send an electrical signal to the firing mechanism, which would confirm an infrared lock on the target. The rocket would then fire, sending it toward the aircraft at 1,600 kilometers per hour (about 1,000 mph).

A Strela-Blok missile would be a real danger in the US. It could be emplaced in darkness, days ahead of time, and the terrorists would be miles away when it fired.

Civilian airliners would surely not be the primary targets. From Andrews Air Force Base fly Air Force One and all Air Force Special Air Mission aircraft (VIP flights). What about security operations on the ground around the base out to three miles?