AS IT HAPPENED. Five years ago, I was up and about early to have an oil change and routine maintenance on my car. It wasn't until I had paid for the service and started my car that I had any inkling of what was going on on the East Coast.
As part of its commemorative coverage, CNN made available a real-time replay of its morning news show commencing at 8:30 am (Eastern.) Celebrity maternity wear, earnings prospects at Nokia, all of a sudden a cut to "disturbing video."
The first person the network reached in New York was their vice president of finance, Sean Murtagh, who observed the first plane from his office, which I believe is upstairs at Penn Station. He described the plane as a "twin engine passenger jet, possibly a 737," and he noted that the pilot was having what he interpreted as control troubles, with the wings rocking. Not bad for seeing something that didn't look right without any inkling of what was to happen, and consistent with an inexperienced pilot flying too low and fast for conditions.
The newscast repeatedly shows the second plane approaching the south tower, but it's obscured behind the north tower just before impact. Newscasters surmise that the jet is "another 737" and their first instinct is that something's wrong with the navigation system???
I suspect observers initially characterized both jets as 737s rather than the larger transoceanic twin-jets because they didn't realize how big the towers were.