The altimeter mapped the route without knowing it
Two of these sectors were not point-to-point — each set down at an intermediate
airport before continuing. Nothing in the logger knows that. But on both, the cabin trace
descends, settles on a plateau roughly 1,100 ft above the departure field
for about seventy minutes, then climbs away again. That plateau is the intermediate
airport's elevation: with the doors open, cabin pressure is simply local pressure, so the
instrument was reading the ground it was parked on. A barometer alone recovered the shape of
the itinerary.
isa datumbmp3902 s sampling
The 787's lower cabin altitude is real, and measurable
Composite airframes are marketed on a lower cabin altitude, and the claim survives contact
with a cheap sensor. The 787-8 held its cabin at 5,995 ft
— effectively the 6,000 ft figure Boeing advertises. The A330-300 flown
the same week ran 7,304 ft, about 1,300 ft higher, for ten hours overnight.
Same passenger, same instrument, one week apart. That difference is the entire marketing
claim, and it is sitting in a CSV on a microSD card.
cabin altitude1013.25 hPacross-check
Power is the constraint, not storage
One sector fragmented across eight reboots. Another lost nearly four hours mid-flight,
taking an entire intermediate stop with it. A fifth was never recorded at all, because the
battery was flat before boarding. Across sixty-two boots the card had consumed
7.6 MB. Everything that went wrong was a power-budget failure wearing a
data-loss costume, which is the sort of thing you only learn by flying the device rather
than bench-testing it.
power budgetbrown-outsd write path