March 29, 2017:
Israel officially commented on the March 17th incident where an Arrow 3 anti-missile missile was used to shoot down a Syrian SA-5 anti-aircraft missile that had been fired at four Israeli jets bombing a target (new weapons for Hezbollah) in eastern Syria near Palmyra. Apparently several SA-5 SAMs (surface-to—air) missiles missed the Israeli jets and instead of detonating anyway (as these missiles are built to do) were headed into Israeli air space and Arrow 3 was fired just in case it was a ballistic missile. The implication was that Syria might have deliberately modified some of their SA-5 missiles to operate as a surface-to-surface missile. This has been done before with Russian SAMs, usually as an unofficial (and crude) modification by Arab users. But there have been some modern SAMs with a built-in surface-to-surface mode. This was done for the U.S. Nike-Hercules system used during the 1960s and later. Other users of the Nike-Hercules (like Taiwan and South Korea) have made this modification and produced an accurate, if expensive, surface-to-surface short range ballistic missile. The Nike-Hercules was designed to be used in surface-to-surface mode. In American service that meant the standard anti-aircraft warhead was replaced with a nuclear one set for air burst over a distant surface target.
The SA-5 is a 1960s design that Russia has updated and Syria received the latest S-200 version of the missile in 2010. This seven ton missile has a range of 300 kilometers but Israel has apparently developed effective countermeasures for it when it is used against aircraft. Missiles like the SA-5 have proximity fuzes that are programmed to detonate when within a certain distance of a target or, if the missile has missed, to self-destruct rather than hitting the ground in one piece (and doing serious damage to something). Russian SAMs, especially older ones, have been known to have self-destruct systems that failed resulting in the missile “going ballistic” and landing intact. These SAMs have also been noted suffering from proximity fuzes that didn’t work at all (because of fuze failure not jamming).
The March 2017 incident was the first time the Arrow 3 has been used in a combat situation and it was also implied that the Arrow fire control system was programmed to automatically assume that anything resembling a ballistic missile headed for Israel, whether intentional or by accident, was a danger to Israel and should be shot down just to be on the same side. Syria responded by announcing that if Israel continued carrying out these air raids in Syria then the Assad government would use hundreds of ballistic missiles (most SCUDs and other Russian designs) against Israel without warning. This is what Arrow was designed for and what the Israeli forces constantly prepare for. For the Assads this sort of attack would be suicidal and apparently Iran forced the Syrians to make the threat and promised to join in. Iran is not normally that adventurous so there is yet another mysterious situation in the Middle East.
Meanwhile Syria has been getting new weapons from Russia. While the SA-5 is a 1960s design it is one that Russia has updated and Syria received the latest S-200 version of the missile in 2010. This seven ton missile has a range of 300 kilometers but Israel has apparently developed effective countermeasures. In 2016 Russia sent in an SA-10 (S-300) anti-aircraft system to protect their troops in Syria. These missiles have about the same range as the SA-5 but are more accurate and resistant to jamming. They may also have a surface-to-surface mode installed, just in case. Mainly the Russians are trying to arrange peace deals in Syria, even for Israel.
The Arrow fire control system was apparently programmed to look for anything acting like a ballistic missile headed for Israel. Thus when something like the SA-5 kept coming towards Israel Arrow automatically acted as if the SA-5 may be deliberately operating as a ballistic missile. That would mean the SAM was aiming for a specific ground target and might even be carrying a more dangerous (poison gas) warhead.