It is theoretically simple. And certainly relatively easier than say landing on the moon - and taking back off - with 60s technology.
There is no fundamental difference between a ground to air missile taking down a plane.
Btw Finn, the largest engineering project in the history of Man is also the most ignored, the ISS
A rogue group getting their hands on a missile, or a country like North Korea blackmailing everyone, isn't the last war.
Pete