When they find out the plane is heading for St. Louis, Ryan says "Cardinal Stadium" and Mack says "Baseball game." The St. Louis Cardinals play in Busch Stadium. Cardinal Stadium is in Arizona.
When the team is trying to stop the plane taking off, there is a sign that indicates that the airport is the Pine Bluff Arsenal airfield. The Arsenal doesn't have an airfield. The closest airport is the Pine Bluff Regional Airport about 12 miles away.
The plane carrying nerve gas goes down in an area of orange groves in the flatlands near mountains. There are no mountains or orange groves anywhere near St. Louis, MO.
When the plane initially takes off, they report the plane heading NNE. Once Brown intercepts the plane, he announces the heading as 028 which corresponds to NNE. A course on that heading from Pine Bluff would pass well to the south of St. Louis. Each time the plane turns, it turns E which would be away from St. Louis. The plot in the TOC shows the plane initially flying NNW which would make the following course changes point the plane toward St. Louis.
The area around Pine Bluff arsenal is mountainous and desolate. The actual arsenal is in the Mississippi River delta. The area around the arsenal is relatively flat and forested.
When Mack Gerhard asks Bob Brown what his altitude is, Bob says "four, and climbing". The next shot of the aircraft's instrument panel clearly shows the altimeter indicating 1250 feet.