A defense system could have theoretically saved Malaysia Airlines Flight MH17, which was shot down by a surface-to-air missile, but experts say it's too costly and unrealistic to equip commercial jets with military plane technology. The reality is that incidents like the downing of MH17 are very rare and it simply wouldn't be practical to ready thousands of planes for an unlikely assault. "Unless we assume the world is at war constantly and all that airspace is a threat, it just doesn't make sense for the commercial world," one former pilot said.
