Comment by someplaceguy | Hacker News Reader

Comment by someplaceguy | Hacker News Reader

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> How were they doing alignment in a hangar to start with, were these roofless hangars?

I don't think so.

You can read more about alignment in page 7, paragraph 10A-23 and the following pages. It'd usually involve using test equipment and manually inputting the current coordinates (e.g. heading, position, altitude, date/time, ...) into the system, from what I understand.

Regardless, the paragraph I mentioned in my previous comment clearly instructs to enable ASTRO mode after the alignment is completed and the airplane is taxiing in the open. It also mentions that in ASTRO mode, the system can confuse the ceiling lights of the hangar for stars (hence why it needs to be disabled inside the hangar), which means that ASTRO mode does track stars on the ground.

I wonder, however, whether it could track stars from the ground during the day. Might well only have worked at night.

The first paragraph of page 40 says: "Stars are normally tracked before takeoff, both at night and during the day (...)".

Now that's a money quote. The following sentence, which says that "If star tracking has not commenced before takeoff, it should start at an altitude where cloud cover and sky brightness conditions have improved.", leads one to believe that it was possible for the sky to be too bright to track stars from the ground sometimes (since it basically says exactly that), but it now seems clear ground tracking during the day was possible. Maybe it depended on the latitude, time of day, and position of the Sun relative to the stars (low latitude in the middle of the day without sufficiently bright stars far enough away from the Sun = sky too bright, higher latitude early or late in the day with sufficiently bright stars far enough away from the Sun = track from the ground, any other combination = results may vary). Actually, I just saw that the bottom of page 42 describes how to handle situations where the sky was too bright for specific stars.

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