Hey i hope u get it sooner or later, i think indeed its this mission and the other one were u have to keep the last two bombers alive and shoot down a german ace with his wingmen plus a few others. On Ace in The Black Heart u need to pilot ace kill this german ace is his me-262 because of the speed difference i suggest using the P-51D kinda talling him so keep behind him he will turn and come at u so dive slightly to dodge his gunfire. At one point he will fly low and thats ur best chance to get him as he,s flying low and also not using full trottle its the best chance to fill up ur ace meter as soon its full click to activate the ace kill and try as quik as possible to get a shot at the pilot, even if this isn,t working first time around he will do this a few times, its like with most boss fights they got a lined out set of movements or paths they take same goes for the german ace. Must admit it took me god knows how many trys to finaly get it. So its def not easy. Good Luck!