I was looking through the questions tagged 9-11 and noticed the no-planes theory isn't on here. So:
Were there planes that crashed into the WTC? Some examples of notable claims asserting otherwise are here , here, and here.
Another article elaborates, and claims the following: (note: these are scattered throughout the article)
The first to notice that American Airlines Flights 11 and 77 were not even scheduled to fly on 9/11
Edward Hendrie has published the data tables for both of these alleged flights, where it turns out that the BTS subsequently revised their tables with partial data in order to cover up their absence.
Even more surprisingly, however, Pilots has also determined that United Flight 175 was in the air in the vicinity of Harrisburg and Pittsburgh, PA, at the time it was purportedly crashing into the South Tower in New York City. This may come as quite a shock to those who watched as it entered the South Tower on television. Indeed, when an FBI official was asked why the NTSB, for the first time in its history, had not investigated any of these four crashes, he replied that it wasn’t necessary “because we saw them on television”. Well, we didn’t see the Shanksville crash or the Pentagon crash on TV, which leaves us wondering what we did see on television on 9/11.
The footage of the South Tower hit exemplifies several anomalies, including a Boeing 767 flying at an impossible speed, an impossible entry into the building (in violation of Newton’s laws), and even passing through its own length into the building in the same number of frames it passes through its own length in air—which is impossible, unless this 500,000 ton, steel and concrete building posed no more resistance to its trajectory in flight than air. Some have claimed that this was a “special plane” that could fly faster than a standard Boeing 767, but no real plane could violate Newton’s laws.