Bob Noel writes:
1) Exactly what is the extent of the connection (physical and logical) between
cabin systems and cockpit systems? Unfortunately, the specifics are likely
to be considered proprietary and not in the public domain.

2) Why have any connection at all?

Top 10 reasons why there is a connection between the entertainment and
flight control system:

10. Each seatback computer has a CPU and RAM in it. Can you imagine
a Beowulf cluster of all of these computers? What a powerful machine!
This cluster soaks up spare machine cycles predict the weather that
the plane is about to encounter.

9. Counter-terrorism. Each seatback can run a flight simulator
program. To increase realism, it gets real data from the flight deck,
making the simulation more entertaining. If a passenger has the magic
unlock code, they can enable the reverse connection -- taking control
of the plane. Normally only the undercover air marshals have the
codes, but if hijackers enter the flight deck then the codes are
broadcast to all of the passengers in the plane.

8. Cool screen savers. In addition to the "plane's current position
on a map" display, you can watch the fuel levels, control surface
deflections, autopilot programming, and current radio frequencies.
The plane compares the pilot's performance to an internal model of an
idealized pilot, and shows the passengers what the pilot is doing
right or wrong. A special game mode lets you pilot a simulated plane
and see if you can out-score the real pilot.

7. Surveilance cams. Each tray table has a built in webcam which
lets passengers videoconference from the comfort of their own chair!
From the flight deck pilots can also turn on any camera they please to
check out suspicious passengers, or to relieve boredom. This data is
also interleved on an uplink to ATC so they can keep an eye on the
sky.

6. More efficient multicast. What if a passenger is downloading a
GPS firmware update, and the flight deck is downloading the same
update at the same time? You wouldn't want to transmit those bits
twice -- if they share a common network multicast can be used to
improve performance.

Okay, I ran out of ideas. Perhaps you can help finish this list?

Chris