During the escape from the underground garage, you can see Geneviève Bujold crawling through the tunnel behind the stretcher carrying her son. In the next shot, you can see Geneviève Bujold and the stretcher carrying her son entering the hole in the wall that leads to the tunnel.
The motorcycle Miles is doing his stunt on, is a Honda XL-250, which has a 4-stroke engine. The sound of the exhaust is from a 2-stroke engine which were used on Yamaha, Suzuki, and Kawasaki motorcycles.
When the airliner is on its way to Los Angeles, the pilot tells the passengers that they are flying over the Grand Canyon, and that he will turn the plane to the right to allow them a better view. In the view from the cockpit, the plane is turning to the left.
In the television version, the aircraft on which the newlyweds are flying, changes repeatedly from a Boeing 707 to a Convair 880 and back again, each time with different airline markings. Nighttime shots of the plane are borrowed from the film Airport
When Miles tries to perform his stunt on the track after the first went wrong, you can clearly see him riding out of the loop again, since the footage used to show the beginning of his new attempt is the same as the first one.
The airliner tells the control tower it is "VFR on top" meaning it is flying in clear weather above the clouds. A moment later, a shot is shown of the airliner in clear skies; no clouds above or below.
The man on the plane that is soon to arrive at LAX, is seen putting the hi-liter down on the arm rest. The next shot has him X-ing next to a paragraph in a magazine article with the yellow hi-liter. The shot changes back again and the hi-liter is back on the arm rest between him and his wife.
During the earthquake sequence when Stewart and Remy Graff shelter under the jeep, the sign 5020 that is on the lobby of the Royce building, falls down, but reappears on the top again in the next shot.
When the motorcyclist's truck arrives with patients and injured boy at the hospital, there is an announcement on the overhead speaker saying there is a desperate need for type AB blood. Type AB+ (positive) patients are universal recipients; they can get anything unlike Type AB- (negative). Additionally, AB- is the rarest blood type in the U.S. (approx.1 out of 170 people). Type AB blood (both +&-) is not usable, except to another person with that blood type. They should be asking for people with Type O (-/negative), as they are universal donors. Type O+ is the most common blood type.
After Miles comes out of the loop on his first try, the left handlebar is acutely bent, as are the gauges. When he starts his second attempt, the handlebar and gauges are restored. Before his second attempt, his assistant says "We only have one more 250," implying that there is another motorcycle.
During the movie, a comment was made that people weren't sure that the atomic bomb would work until they dropped it. In fact, the first atomic bomb, detonated on July 16, 1945, was mounted on a tower and not dropped.
After the stairway has fallen away in the skyscraper sequence, an office worker manages to hold on to a girder before falling to his death. As he falls through a giant pane of glass, the airbag is clearly visible under it and actually shoots out of the top of the frame.
The exterior of the parking garage falling apart with the aftershock, is a combination of miniature on the top and live action at the bottom. The debris falling off the miniature disappears behind the live action on the bottom.
During the quake, Bill Cameron looks out the window of the skyscraper he is in to see two men fall out out of a neighboring window. As they fall, they both disappear behind the matte separating the building facade and the minuature of downtown Hollywood.
The goof item below may give away important plot points.
When the dam elevator opens, the water floods out carrying the drowned maintenance worker. You can see the actor forcibly blow out air from his mouth as he hits the floor with all the water around him.