[Alberta's Child]

One interesting angle to this whole thing is that it's not as easy to shoot down a passenger aircraft as you might think. Although they are larger and much slower than military jets that SAMs are designed to take down, they also give off far less hear than the engines these SAMs are designed to track.

[Alberta's Child]

Far less heat, that is.

[Darksheare]

From underneath, the landing lights/forward illumination would have put off far more heat than the engines.
Any manpads launched would have gone for what it could see, the lights by the center wing tank.