It is assumed the sequence with the plane departing was filmed at the Ft. Lauderdale Airport. The airport has since been renamed the "Ft. Lauderdale Hollywood International Airport".
However, as all filming locations are in Los Angeles, the airport used was more than likely LAX, the primary airport in Los Angeles, and one of the busiest airports in the world.
Ironically enough, LAX was more than likely the one Elaine was to arrive at, upon arrival in Los Angeles. It is also more than likely that she rode the taxi from the airport straight to the hotel.
Note that this scene technically doesn't count as a location, even though its presense was required in order for Elaine's trip to advance.
While we never see this location, we know that it is implied, due to the image of the airplane lifting off.
We can make the logical assumption that this plane was either filmed at the Los Angeles International Airport for this film, or that the flight sequence was of generic, stock imagery. Due to the ominous compliment of the imagery, music and subconcious plot elements, it is more than likely that these shots were crafted specifically for the film.