>>..... TWA800 would have been a relatively easy target for a Soviet SA16/18, which even then was 15 year old technology.
No it wouldn’t have been.
http://www.fas.org/man/dod-101/sys/missile/row/sa-16.htm
http://www.fas.org/man/dod-101/sys/missile/row/sa-18.htm
I based my comment on the following:
[1] The specs given for the original SA-18 omit mention of any system upgrades over the period of 13 years that intervened between the introduction of the SA-18 in 1983 and the loss of TWA800 in 1996. In any case, “official” performance data for new and active service weaponry of any nation is notoriously unreliable.
[2] Even at the officially specified 3500m max altitude capability, TWA800 was within engagement parameters.
[3] TWA800 was an absolutely ideal target: a large non-maneuvering a/c climbing at relatively slow airspeed, a huge IR signature with its multiple engines at high throttle for the climb, zero counter-measures in play, and an optimal dark sky background offering no distractions to a missile seeker.
[4] As I learned over the weekend, the SA-18 also possessed targeting logic that would terminally guide it to strike the airframe rather than to an IR hotspot.
I recognize that others may disagree with my assessment, but I stand by it.