Heroes Over Europe

To get this achievement you must enter Ace Mode and Pilot Ace Kill an enemy boss. A Pilot Ace Kill is when you kill the pilot out of the cockpit rather than shooting the engine(s) or an Ammo box. Depending on the difficulty that you're playing on, this can prove to be very frustrating. Do not get the bosses confussed with the enemy squad leaders that you're introduced to in the 1st mission, Phoney War. You'll be clued to the presence of a Boss by their health meter that will appear in the top right hand corner of your screen. The squad leaders are marked with a yellow iron cross icon within the normal red target triangle. The Bosses are marked with the same yellow iron cross but underneath that there will be a few chevron shapes (^'s that are stacked on top of eachother). There is only one other plane in the game that has this marking that is neither a boss nor an ace. You shouldn't get that plane confused with a boss as a helath bar won't appear. Not to mention that you won't be able to progress through the misson if you perform an Ace Pilot Kill on that particular pilot.

There are a total of 4 bosses in the game that you'll encounter. Below is a list of them in the order of appearance. Hans Werner flies an Me 109 E-4 in the mission 'Empire's Heart'. Ernst Jager is in an Fw 190 A-8 in the mission 'The Butcher's Birds'. Ernst Jager makes a reappearance this time in an Fw 190 F-8 in 'Eye of the Storm'. The final Boss is Johann Sturm who pilots the Me 262 A2 Ace in the final mission 'The Black Heart'.

Tips:
Once you enter Ace Mode while targeting a boss they will usually and almost immediately start to do barrel rolls to evade. My method to open up that Ace Pilot Kill shot is to tail the enemy letting the Focus meter fill up until they get ready to bank and change directions. Right when they start to roll for their next turn I'll then enter Ace Mode. More times than not, that would open a perfect shot that will give you a direct line of sight on the pilot as if they were sitting in a chair and you were above them looking down into their lap. If you enter ace mode while traveling in a straight line behind the enemy you will not be able to see the pilot and would be a waste of the focus meter. If you try to go at the enemy head on there is a high chance that they shoot at you causing you to lose your "focus" preventing you from entering Ace Mode. Just be patient and take your time to make sure that you have that kill shot lined up. If you miss, you will have to fill the Focus Meter again and start over. Keep in mind that you only need to fill the meter to its 6 o'clock position before you are able to enter ace mode. This won't give you much time but sometimes that's all you're going to be able to fill up before the boss shakes you off. If you are having a hard time with the the pilot ace kill there is no shame in playing on the rookie difficulty. Hopes this answers any questions that you may have had. If not feel free to send me a message and I'll do what I can to help out.