N591UA and N612UA
There have been claims, for many years, that the four 9/11 crash sites were not as they seemed. These range from the view that the observed damage at one or more sites wasn't caused by a plane at all, to the acceptance that an aircraft was involved - but not one of the hijacked flights. Critics of these ideas always wondered what happened to the original planes, but one particularly surprising answer has been presented: they're still flying.
The registration numbers were in fact cancelled eventually, but not until 2005: see the record for N591UA and number N612UA. It could be argued that this was a response to being "exposed", an attempt to cover up the truth... If it wasn't for the fact that other planes didn't similarly remain registered for years after being destroyed. Here's an example.
Destroyed, then? So then we visit the FAA Registry, enter the number, and this record pops up as of 10th September 2007:
An FAA Registry check on 10th March 2006 tells us:
(It finally seems to be acknowledged as invalid by September 10th 2007.) Interestingly, the model here is listed as a PA-31-350, while the NTSB report calls it a PA-31-250. It’s the same owner, though, so we’d suggest it’s probably the same plane. (And if it isn’t, this only shows the N-numbers can be reassigned, which doesn’t support Holmgren's case, either).
Then we went for a third, and quickly found this:
And yet the FAA record as of 10th September 2007 says:
Here’s an accident from 1987:
But as of September 10th 2007, it’s still showing with a “Valid” status, assigned to Continental Airlines:
Almost 20 years after being written off, yet still registered? A valid N-number is clearly not evidence that a plane is currently flying.
But what about the "UA employee" who let slip he'd flown on the plane? Well, he isn't an employee of United Airlines, and he doesn't have much interest in conspiracy theories. In fact his page ended with the comment:
Still, he does note that he flew on a flight with the registration number N591UA on 4/10/2003. Could this be true? We checked at www.bts.gov, and it seems not. The plane taking that flight is on record as being N594UA.
So you can choose to believe that the conspirators allowed the planes to keep flying, without changing their numbers, even though they would be observed, photographed and filmed by thousands upon thousands of passengers and plane-spotters. The latter who would spot and expose this immediately, yet mysteriously have failed to do so.
Or, you might think this person made an error, perhaps misreading a 4 as a 1 when he came to type up his notes. That's by far the most likely explanation to us, but of course it's your call.