In this blog entry I postulated a duplicated United 175 at Logan Airport that took off at 8:23 besides the official one departing at 8:14. Moreover, the 8:23 flight was apparently tracked by United Airlines as Flight 175 while the FAA tracked the 8:14 flight, as I have shown here.
For obvious reasons, tracking two different planes with the same call sign is an absurdity in the world of air traffic controllers. It would inevitably lead to confusion and raise the danger of accidents.
It is therefore reasonable to establish the working hypothesis that the clandestine United 175 (take-off 8:23) identified itself to the controllers with a different flight number. Unfortunately, this hypothesis, if true, looks hard to verify.
This being said, I spotted a possible candidate. On 9/11, Mark Randol was manager of the Civil Aviation Security Field Office (CASFO) in Washington, DC, a subdivision of the FAA. He reported to the Commission:
By 9:25 AM, Marcus Arroyo (Regional manager) called to report several hijackings, including AAL #77, UAL #175 and UAL #177, and he made it clear that this was a terrorist act. Randol then immediately tasked his staff to find out everything they could about the flights. Randol remembers that the whole day was hectic. By 9:45 AM, they had identified that AAL #77 had departed from Dulles, but they could not confirm whether it had been hijacked, while they discovered that UAL #177 was being held at the gate in Boston.
http://media.nara.gov/9-11/MFR/t-0148-911MFR-00969.pdf
The BTS database tells us that United 177 was scheduled to depart at 6:55 pm from Boston, destination Los Angeles.
http://www.bts.gov/xml/ontimesummarystatistics/src/dstat/OntimeSummaryDepaturesData.xml
This raises two questions:
1) Why was it reported hijacked?
2) Why was it reported "held at the gate" if its departure was only in the evening?
Misinformation #1 alone could be dismissed as a transmission error induced by the confusion that day, but putting it together with misinformation #2 creates the impression that the existence of the plane posing as "United 177" was being smothered up.
Most remarkably, the hijacking of United 177 was reported at 9:25, two minutes after Ed Ballinger, United flight dispatcher, sent the last message to "his" Flight 175 while it was over Pittsburgh. It is therefore legitimate to specify the above working hypothesis: The plane that was tracked by United Airlines as Flight 175 was tracked by the FAA as United Flight 177.
