Part 1: files.abovetopsecret.com...

Full Align procedure, approx. 10 minutes, at high latitude approx. 17 minutes :
Part 2: files.abovetopsecret.com...

Fast Align procedure, approx. 30 seconds :
Part 3: files.abovetopsecret.com...

So, fast align could be done very fast by just positioning selectors to ALIGN and then repositioning selectors to NAV. However, greater navigational accuracy was attained by entering the present position.
Can it be that one of the pilots was bored or was in learning mode, and played around with these selector knobs?
Or did they worry that too much drift was accumulated during parking while in the taxi lanes, and therefore did all those fast aligns? It seems a pretty fast method to me, lasting even much shorter than the 30 seconds which stand for it. Click, click, ready.
Now I am gonna re-read your complicated post, to try to comprehend what you were steering at.
I was simply pointing out, that there is hard evidence from that FDR positional data, corrected for accumulated drift, that AAL77 in fact really departed from its original Gate D26.
And may I point out too, that I seem to be the only one in 9/11 forum land up till now, who found that out (assisted of course by the precluding fine work of Jan Zelman, an analytical mind, just as mine).
Not one of you, the professional pilots, dared to confront Balsamo with his misguiding northern departure gate stories. Which he still maintains at his board's main pages.
So, why the condescending tone? Laymen can be having fresh insights, as I proved with the above corrected taxi lanes trajectory for AAL77 departing from Dulles.
Which has in my opinion nothing to do with flying a 757, that's why I can come up with that solution for the nagging PfT Gates confusion.
I did my best to quickly repeat from memory, what I have grasped from all the professional input regarding flying a 757-200. And that in a language which is not mine. Meant for other laymen. Not for pilots. As can be seen, when pilots start talking their trade, we have difficulty to grasp their vocabulary. But a quick view in the Manuals brings us back at pace, most of the time.
I took especially notice of the sentence "" A full alignment must be accomplished when the time from the last full alignment to the completion of the next flight exceeds 18 hours.""
Well, that never happened for AAL77, it flew all the time (years) vice-versa from IAD to LAX and back, arriving back at IAD in the early evening, and departing in the early morning. Never exceeding those 18 hours. Thus, no need for a full align, when I, as a layman, read that Boeing Flight Manual text near the top of my linked to, IRS Part 3.
Because even a very fast align would suffice, since the IRS remembers the evening data, when it is started up again in the morning, after being towed with no electric power on, in the night, around the C and D Concourse building from its northern arrival gate, and down to Gate D26.
But for the sake of clarity, let's make a first full align in the morning. That's thus "the last full alignment". Then we fly 6 hours, land and park at a LAX gate. And depart from LAX f.ex. 4 hours later again. No need for a full align at LAX, no 18 hrs spent there. Arrival at IAD again 6 hrs later, parked at northern gate, power off, towed in the night to D26, power on in the early morning, no 18 hrs spent at IAD, no need for a full align. Etcetera ad infinitum.
I can imagine however the strict airline rule for a full align after each engine and APU start up, but according to the rules description in the Inertial Reference System part of the Boeing 757 Flight Crew Operations Manual, (my linked to Part-3), it was not even necessary.
A fast align with entering present position sufficed, since the 18 hours boundary was never crossed. And at wheels off from the runway, the plane's lat.-long.-position got very fast updated anyway.
See the map of the first minutes after AAL77 departure from Dulles, posted by Balsamo in disguise, a few page back, with the fast drifting together positions, listed in there. You see them come together pretty fast after take off. That means that first in-flight positional update takes little time to correct all drift faults. It's an update, not an in flight alignment, that's possible for civilian planes only after 2002.











