When Elaine and Jerry have to get on another flight because there is an issue with theirs, they are told that there is one seat in 1st class and 1 in coach. Elaine took the coach, Jerry took the 1st class.
1) When Elaine comes back from using the restroom, the guy next to her said that he thought she had switched seats. Impossible on a full flight.
2) When Elaine sneaks into 1st class, she finds an empty seat to sleep in. Impossible on a full flight.
At the end of the show, Jerry and Elaine are at baggage claim waiting for their bags. Jerry gets his but Elaine's is shown to be at baggage claim in Honolulu. There is no way that a flight could make it from St. Louis to Honolulu in the same time it took to go from St. Louis to New York.
Jerry puts only one slipper on Tia's foot.
Kramer decides to take the Long Island Expressway to JFK Airport. That expressway does not lead to the airport. George's route of Grand Central to Van Wyck is correct.
Elaine's seat is near the rear of the plane, which is obviously not the location the flight attendant gave her, 3rd row right.
Kramer would not have been removed by security. Removal of disorderly passengers are done by police officers.
Meals are only served on long flights usually over 2 hours. From St Louis to New York is just under 2 hours. Not only is the food wrong but the episode is played out as if they are on the plane for many hours. Also first class isn't treated that much better than coach unless it's a top of the line airline.
Jerry and Elaine have to take a different flight back to NY. Jerry takes the first class seat while Elaine gets stuck in coach. However, in all exterior shots of the airplane, it's obvious it is a Southwest Airlines plane. Southwest does not have a first class.
Despite the airline clerk's claim that the replacement tickets given to Jerry and Elaine were "the last two seats available": Elaine unsuccessfully sneaks in to an unoccupied first class seat. This is inconsistent with the clerk's claim but is an accurate depiction of airline procedures. Jerry's ticket was upgraded only because the shortage of coach seating and Elaine's ticket was not upgraded due to the available seat in coach. In fact, it's unlikely an airline would upgrade a passenger's ticket, even in the event of cancellation. Additionally, the clerk likely lied to hide the reality that he could have upgraded Elaine's ticket.
When George is buying the Time magazine, Kramer shows up at the news stand telling George that Jerry and Elaine are on another flight. As this is before cell phones became widespread there was no way that Kramer could have gotten that information. He could've gone to the information counter, or maybe Elaine or Jerry called from the air and had George or Kramer paged (Jerry would not be surprised that Kramer was with George during the pickup). Or, although this is less likely, Kramer might even have a mobile phone (given his character, it wouldn't be a surprise). Or perhaps he had a beeper that they used. There are a number of possible explanations.
Throughout the scene where Jerry (Jerry Seinfeld) and Elaine (Julia Louis-Dreyfus) are racing through the airport to get to their flight, the run past a sign that reads," Gates 24-40". Following that, they can be seen running down the same passageways and past the same sign again.
There is an out of sync misplaced piece of audio as George knocks on the planes toilet door, a soft yell can barely be heard as George yells "Ahh aw, Kramer Help" -"Hey buddy", a few seconds later George gets pulled into the toilet by the killer, yelling " Ahhh Kramer".
George plans his pickup so he arrives at the airport right as Jerry arrives. Jerry's plane is changed to a flight to LaGuardia and George find this out after being a half hour late to pick up Jerry. The plane then goes back to Kennedy instead of Laguardia. If George arrived a half later than Jerry should have landed that means Jerry's plane was in New York airspace at the time. On the plane during the moment they had meal time and enough time for a nap. There is no way they were in the air that long above New York.
Jerry and Elaine get the "last two seats, one in First Class and one in Coach" but, later on there is an empty First Class seat one row behind Jerry (and the model) which Elaine later tries to occupy but gets sent back to Coach.