Reply #56: The 2nd plane had no foreknowledge

[KDLarsen]

However, the passenger whose call was put in doubt by the OP, made the suggestion himself that he thought they might fly to Chicago and crash into a building there.

The plane decended about 34,000 feet in about 7 minutes. That's a very fast decent and if the engines were at full throttle, the passengers most likely put two and two together and realised that they weren't going to land at an airport.

ETA: Barbara Olson appears to have been the first passenger to be told, that two planes had crashed into the WTC towers.