American officials believe the missile that destroyed Malaysia Airlines Flight 17 was fired by pro-Russian separatists in Ukraine, using a Russian-made system designed for bringing down fighter jets. That brings up the question: How easy is it to bring down a passenger jet with a weapon that's meant to used by trained soldiers?

Turns out, it's pretty easy. As in, take a three-day course and go for it easy.

The weapon in question is the SA-11, a radar-guided surface to air missile (SAM) system. It's been around since the Soviets deployed the first-generation model in 1979. The mobile system (it sits on a tank chassis) is made to serve near the front lines to protect ground forces from air attacks. Operated by a crew of four and designed to attack fighter jets, it can fire multiple missiles simultaneously. It fires high explosive proximity fuse warheads, which home in on their targets and detonate just before reaching them, to maximize damage. Targets 20 miles away and over 70,000 feet in the air are fair game. It’s a “big, heavy vehicle that has big missiles,” says Randal Cordes, a military intelligence analyst who has worked at the CIA and Pentagon. “To use an SA-11 against an airliner, it’s brutal overkill.”

Inside of a Buk-SAM. Wikimedia

The training required to properly operate the system can take weeks or months, which may explain why the Malaysia plane was destroyed in the first place. The problem with the SA-11 is that it’s difficult to properly identify and track targets, but easy to fire missiles. “The skill comes in knowing what you want to shoot at,” says Cordes. That’s because the SA-11’s radar system shows the same “blip” for all different targets. The operator sees an aircraft’s altitude, air speed, and vector, but not it’s size or type, says Anthony Cordesman of the Center for Strategic and International Studies. Airliners broadcast a four-digit transponder known as an IFF code that identifies them as civilian aircraft, and the SA-11 system is capable of picking up that information. But the training that goes into properly identifying aircraft takes months, especially since the window for acquiring and firing on targets is just a few minutes.

“You can’t take a crew, stick ‘em inside the cabin, and say here’s the on switch, and here’s the button you hit,” and expect them to operate it properly, says Wesley Paul, a former intelligence research analyst for the Air Force.

"Ready" and "aim" are difficult. "Fire" is easy.

But say someone dropped off the SA-11 and did all the basic work of getting it up and running, another complicated task. And say you decided on a target that popped up on your radar, whether or not you knew what it was. In that case, destruction comes easy. It would take three to four days at most to teach someone to use the system well enough to shoot down a 777, Cordesman says. That’s partly because passenger planes fly at steady speeds and altitudes, and have no defense systems. They cruise higher than fighter jets do, at heights where they’re more easily picked up by radar.

“Once the radar picks up a target, it is a matter of telling the system that it should engage the target and issuing a fire command,” says Paul Huter, an aerospace engineer at Lockheed Martin. That involves following a checklist and selecting the target, either by clicking on a screen or pushing a button (or clicking with a mouse on a screen, depending on the system model). Training would consist of running through that procedure in various conditions, and would be so straightforward, Huter says, that “it is certainly possible for someone with no training to read through the checklist and successfully engage a target.”

Cordesman compared it to firing a gun: “Pulling the trigger is easy. Judgment is hard.” And once the missile’s been fired, there’s no way to divert it, he says. “You press the damn button and it’s gone.”