Continuity mistake: In the dining scene where Howard Hughes' girlfriend has a sundae sitting in front of her, the cherry which is on top of the sundae changes positions in several different shots. First, the stem is turned towards the left, a few shots later, it is turned towards the right, then left again. It also shows up in the bottom of the dish, then in the next shot, it is back on top of the sundae.
Continuity mistake: When Hughes and Odie are talking about mounting a camera on a biplane and removing one of the wings, the shots alternate between a back view of their heads and a front view of their faces. Odie's head position has no relationship to the one it had in the preceding angle in most of the cuts.
Revealing mistake: Early in the film, when Hughes and another guy are walking past one of the replica WW1 aircraft used for the "Hell's Angel" scenes, you can see the ends of the cylinders of the modern air cooled engines they used to power it. The original aircraft (SE-5A) used a water cooled V8 which wouldn't have been visible.
Revealing mistake: During the filming of 'Hell's Angels' Howard gets the idea to build a single wing mono plane. He and another take an axe and smash the support holding up the upper wing. If you notice the upper wing is already broken, hinged and a very poor covering has been laid over the joint. It is very obvious and noticeable in a few shots leading up to this.
Continuity mistake: When Howard asks L.B. Mayer to loan two cameras, we first see Mayer and his associates from Howard's viewpoint as he is approaching them, and Mayer is standing with the bar on his left. In the next shot Howard greets him, and the men in the group have changed places, with Mayer now facing the other direction and now the bar is on his right.