Phuf opening up a proper can of worms now, but this is what it's about.
If a tau hits with a marker light it can elect a vehicle to shoot a seeker missile at the target. It does not need line of sight and has infinite range. The rule for firing a seeker missiles is as follows.
The shooting is resolved normally in all regards at an assumed Ballistic Skill of 5
Now the question is, what would a seeker missile need to hit a flier?
Some people argue that codex overrules rulebook and interpret that rule as "always hitting on a BS5".
The only thing the FAQ says is
Q: If a vehicle is reduced to Ballistic Skill 1 (because it is Shaken, Stunned, for example) do its seeker missiles fire at Ballistic Skill 1 or Ballistic Skill 5? (p29)
A: Ballistic Skill 5.
Now the counter argument (and where i stand in the matter personally) is the following. It does not mention anywhere that it has the skyfire rule or that it ignores the hard to hit roll. In fact, the rule states that the "shooting is resolved normally in all
regards". Also the FAQ only mentions if the vehicle is reduced to BS1, and is only emphasising the fact that the BS of the vehicle is independent from the BS of the seeker missile as they are two separate things.
The thing is GW is never consistent with their wording and could clarify this in an FAQ with ease. But they rather we rant and rage about it to each other and ruin our games over it lol.