(at around 16 mins) You can see The Red Baron with his goggles on, but they disappear in the next scene.
During the film, the mole on Lothar Von Richtofen's face changes from right cheek to left cheek, then back again.
During the funeral scene at the beginning of the film, the German pilots throw a crown of flowers from the plane, and the crown falls with the ribbon downwards, no inscription visible. Next shot, the crown is shown well arranged, with the ribbon upwards, reading "to a friend and enemy".
As Roy Brown is carried off from his downed plane, Richthofen's hat is skewed jauntily to the right on his head. Nurse Käte Otersdorf says, "Thank you, you saved this man's life." In the cut to Richthofen's reply, "No, I shot him down," the camera frame is flipped horizontally and his hat is now skewed to the left. Also, the tree in the background can be seen to his left instead of to his right as in the previous shot. The camera then cuts directly to a shot behind him and the hat is instantly skewed to the right again.
Roy Brown is shown in a Royal Flying Corps uniform, and describes himself as being in the nonexistent "Royal Canadian Flying Corps". He was in fact a Canadian serving in the British Royal Naval Air Service, and would have worn a naval officer's uniform.
Lothar von Richthofen, the Red Baron's younger brother, was not (as in the film) flying with him on the day of his death (April 21, 1918). In fact, Lothar's plane crashed on March 13 and he was hospitalized because of injuries. Lothar learned about his brother's death while he was in hospital.
The large scale air battles between scouts of squadron strength at night - as shown in the film - could not have taken place in WWI. The airmen would hardly have been to see anything at night, not to mention distinguish friend from foe. Night missions in WWI were largely confined to attacks by a few planes on large targets like Zeppelins, or large bombers which - because of the nature of their missions - had to continue on fixed and predictable courses. Even in the Second World War, over two decades later, night actions remained a chancy business - even with the use of radio and radar. Even then, night fighters usually needed crews of two or more - they were needed for navigation, operating radio, etc. It was well after WWII that technology had advanced far enough to enable planes to locate and destroy the enemy under conditions of almost complete darkness.
The opening scenes of the film show a young Manfred apparently "taken" by a plane flying overhead, as if this set him on a course to be an aviator. In fact, he spent the first several months of the war in a cavalry regiment and applied for transfer to the air force out of frustration - his regiment's duties had become non-combatant.
Manfred von Richthofen is depicted as instructing his men to shoot the planes not the pilots, which is the reverse of his real policy. This was not out of brutality, but practicality, as killing the pilot is the most efficient way to preserve one's life in that situation. It was in fact Werner Voss, represented here by Til Schweiger, who followed the principle attributed to Richthofen in the film.
Kaiser Wilhelm II did not speak English with a German accent; his mother was Queen Victoria's daughter who was also King Edward VII's older sister, and he spoke English like a member of the British Royal family, which he was. However, as most of his dialogue in this film is "translated" from German, his German accent may have been the producers' way of representing that fact.
Richthofen is presented with his Pour le Merite in January 1917, but the weather shows it to be warm and sunny, not winter weather like it should have been. Also, the trees in the background are in full leaf, looking more like the scene was shot in May or later.
In the air battle scene shortly after Ricthoffen & Brown chat in no man's land. One of the British Bombers is depicted with "Royal Mail" on the side of the fuselage. However the Logo painted on the side is taken from the Modern Royal Mail logo, introduced in around the late 1970s.
German soldiers are seen marching through Lille, France, in February 1917, with the spiked pickelhaube helmet. Actually, for front line soldiers the spikes were removed after the first few months of the war. By 1917 most German infantrymen had the new Stahlhelm 'coal-scuttle' helmet.
In Lanoe Hawker's final scene his aircraft seems to change during combat. In the movie Hawker flies and is eventually shot down in a (anachronistic) S.E.5. When Hawker is being chased by Richthofen the camera switches to a rear shot of Hawkers plane. In this scene Hawker is not flying a S.E.5 but probably an equally anachronistic "Sopwith Camel" (or any plane other than S.E.5) judging by the shape of the latter's wings. When Hawkers aircraft is hit and starts to smoke he is seen flying a two-seater with an observer/gunner in the rear seat.
On the ground Hawkers aircraft switches back to the S.E.5.
The British aircraft in the film's first dogfight should have been DH.2 pusher aircraft (rear-mounted engine to allow a forward firing machine gun with the lack of interruptor gear) . The DH2 was the best fighter aircraft at the RFC's disposal in early 1916 and it was what Lanoe Hawker was flying when he was shot down; it certainly looked nothing like an SE5a, the aircraft in the film's dogfight. The German pilots then examine the wreckage of an 'RE8', again not in service until later in the war, plus the smashed up aircraft being examined looks nothing like an RE8 anyway. Since the flying scenes were obviously CDG images, it can't have been that difficult to have done some simple research and then represent the aircraft more authentically. Clearly, however, it was.
The British made S.E.5 flown by Lanoe Hawker was not active in 1916 as depicted. It only became operational in March 1917.