Close-ups reveal that The Phantom is wearing black makeup around his eyes under the mask. When he removes his mask at the end of the film, his face is clean.
When the Phantom is flying the biplane, the long shots show him wearing a shoulder belt, but in the close-ups he is not wearing any safety belts.
A shot of the taxi in city traffic shows a one-way street, but the close up in the taxi shows two-way traffic out the rear window.
When the Phantom has hijacked the plane after his daring rescue operation, the captors fire bullets at the plane, hitting the wing and causing leaks. However in the shot following it, the wing shows no sign of damage.
The motorcycle changes during the prosecution from one with two red lights over the front light, to one with two red lights at the sides of the front light, and then back again.
The float plane used to take Drax from New York City to the Devils Vortex (somewhere off the Malay Peninsula) is a Beechcraft Model 18. The range of this aircraft is 1200 miles. The plane could not fly the approximately 10,000 miles without stopping to refuel at which point the Phantom would most likely have been seen hanging onto the float by someone.
Even if the plane could have made the full flight non-stop, with its top speed of 225 MPH, the Phantom would have had to hang on to the pontoon spar for nearly 2 days.
A horse cannot gallop fast enough to overtake an airplane. Since the men could not see the airplane while riding through the forest, it is unlikely that they would arrive at the exact spot where the airplane crashed.
The Martin M-130 "Clipper" aircraft depicted in the movie never existed. Only 3 were built, all flew for Pan American, and were named "Hawaii Clipper", "China Clipper", and "Philippine Clipper". The aircraft in the movie is named "Orient Clipper". None of the 3 M-130s survived WW II.
Obvious stunt double just before Diana jumps off the sea plane, her hair style, color and face are different
Obvious safety belt on the Phantom while getting on the horse from the plane.
As the Phantom continues chasing the grave robbers on horseback, he reaches up and grabs a tree limb and pulls himself into the trees. The limb is obviously a metal bar with vine like material wrapped around it. This is reinforced in the next closeup shot. The limb is perfectly round and straight.
After the Phantom escapes from the truck hanging from the rope bridge over a gorge, it falls into the gorge and explodes. The explosion occurs just before the truck hits the water.
During the chase scene between the Phantom (on a horse) and two Police officers on motorcycles, when the bullets fired from the officers' pistols hit the nearby trees, they produce sparks.
The Phantom/Kit Walker is armed with two "longslide" 1911 .45 auto pistols. The "longslide" 1911 didn't exist until several decades later than the time period the movie is set in.
In the pan shot of the Pan American dockside terminal when Diane Palmer is boarding the Orient Clipper you can clearly see a modern window-style air conditioning unit sticking through the front wall of the terminal building. Such units did not exist in the time period in which this movie was set (late 1930s).
The motorcycle cops are riding motorcycles with body parts from Indian motorcycles from the '40s when the movie takes place in the '30s.
At the end, when the plane is flying away, the blades of the helicopter filming the plane are visible at the top of the screen.
Reflected in the trunk lid of the cab.
Los Angeles palm trees can be seen reflected in the trunk of Al's cab as he makes a U-turn in New York.