Reply #3: FWIW, the assertion is that we know these messages were received

[OnTheOtherHand]

(I'm pretty sure you know that already -- I'm just filling in for anyone who might be curious.)

P911T cites the United dispatcher who sent many of these messages, who reportedly told 9/11 Commission staffers that the time stamp at the end of each logged ACARS message is the time that it was received (which P911T takes to mean: received by the plane).

This is really unconvincing. P911T states, "An ACK or NAK should be present denoting received or failed, respectively, according to standard message formats. Unfortunately, these standard codes are not available in the above messages." Well, I don't claim to know anything about ACARS, but I did take the time to read the documentation page P911T linked to, and I call bullshit. According to the documentation, the uplink message would contain a block identifier, and the corresponding downlink message (if any) would contain a technical acknowledgement identical to the block identifier (not a binary "ACK"). Clearly the log referenced by P911T doesn't include either of those things -- or any of the field codes in an ACARS transmission as described on this page. P911T appears not to know what is logged in the log.

Presumably the time stamp indicates when the message was logged by the ground network -- not when (or whether) it was received by the airplane. The only way to get to P911Truth's conclusion is to demonstrate that messages aren't logged until they are acknowledged. (That doesn't facially make sense. Would anyone here design an email program that didn't log sent mail until and unless a receipt notification came in?) The dispatcher's paraphrased, ambiguous statement about the time stamps falls far short, especially since there is no obvious reason for him to be an expert in how ACARS logs treat messages sent to planes that no longer exist.

As for how the messages were routed, again P911Truth doesn't seem to know much.

...why would the Central Processing System ever choose PIT as the next ground station for routing purposes if the aircraft was being tracked by the ACARS network to NYC? The answer is, it wouldn't.

This is a lovely example of assuming what was to be proved. The message in question was sent about 20 minutes after UA 175 crashed (or, for the sake of argument, supposedly crashed) in New York City. How, then, could "the ACARS network" be tracking it? More generally, the authors seem not to realize how threadbare their account of the "Flight Tracking Protocol" -- based on a newsletter article that describes services available to customers, and a context-free quotation attributed to an "ACARS Expert" (is that a certification?) who happens to be a member of P911Truth -- is. Actually, P911Truth appears to have invented the phrase "Flight Tracking Protocol." This does not inspire confidence.

Charitably, it's weird that the folks at P911Truth don't seem to have much clue what would count as good evidence for their assertions, or even evidence of their basic competence. Less charitably, maybe they don't care.