So my question relates to the german ignition attack rule inlay that states (translated by me):
"If the ignition token is on the field, the corresponding ship must, if possible, attack a ship in its special firing arc with its first attack."
Now, an attack is possible if a ship is in arc and the defending hull zone is in LoS. If the ship is outside of attack range you may roll 0 dice, but the attack is still possible.
As such, as long as there is a valid attack target in the Onagers ignition arc it has to attack it as the first of two attacks, even if it does not role dice in the attack, the ship may even be on the other side of the board.
Correct (pending english translation)?