4 ms·

That's a good question, one example I can think of is the TV channel on some aircraft that displays positional and airspeed information to passengers. I assume

That's a good question, one example I can think of is the TV channel on some aircraft that displays positional and airspeed information to passengers. I assume this data comes somewhere from the flight computers.

gizmo686 12y ago
Probably, although if you were paranoid enough (or required by regulation), you could airgap the TVs and give them information through a normal GPS system (minus the artificial altitude restriction), or have a hardware unidirectional data path. More reasonably, you could consider the TVs part of the flight system network (with many of the same protections to prevent someone from physically opening one and hacking), and still have an airgapped wifi network.
- StavrosK 12y ago
  What altitude restriction? My phones' GPS works fine in flight, I use it a lot to check speed and altitude.
  - klodolph 12y ago
    Yeah, the altitude restrictions don't really apply to commercial flight. You can conduct a test yourself, you just need to get a little higher and travel a little faster than your typical 757. Try attaching your cell phone to a rocket travelling over 1200 mph or above 60,000 feet, you'll find that your GPS unit basically shuts down. That's not to say that your GPS hardware is incapable of operating under those parameters, it's just designed to shut down so it can't be used to guide ICBMs. Commercial airplanes typically operate at half the altitude and speed which would trigger the condition.
    - MichaelApproved 12y ago
      Don't both speed and altitude trigger the block? The gps must be over a certain altitude AND be going faster than a certain speed.
      - callesgg 12y ago
        It is one or the other.
      - proexploit 12y ago
        IIRC, the legal requirement is to shut down with both conditions are present, some GPS manufacturers simply found it easier to implement each restriction separately.
      - michaelt 12y ago
        According to [1] some manufacturers apply this limit when both speed and altitude limits are reached, while other manufacturers disable tracking when only a single limit is reached. The limits are 1,200 mph speed and 18,000 m altitude. Google tells me a 747's limits are around 615 mph and 14,000 m; Concorde's limits were closer to 1,350 mph and 18,300 m. Still, I'm sure if you're making an airliner you can get access to GPS receivers that will work even at maximum speed and altitude! [1] http://en.wikipedia.org/w/index.php?title=CoCom&oldid=608893426#Legacy http://en.wikipedia.org/w/index.php?title=CoCom&oldid=608893...
    - kalleboo 12y ago
      Do the limitations also apply to GLONASS which is now in all modern devices?
sjwright 12y ago
For stuff like positional and airspeed information, it would not be difficult to design a connection that is physically limited to one-way communication. It would also seem sensible that any interaction the pilots might want to perform on the cabin computer systems could be done by giving them a terminal on that network.
- com2kid 12y ago
  For some stuff that did have data sharing there was a very tightly controlled pipe. Oddly enough it was Linux on one side and Windows on the other. The level of scrutiny that IPC (inter-processor communication) channel got was insane. It is probably one of the safest IPC channels in existence! Unfortunately I didn't fully grasp what systems it was connecting, aviation is full of its own parallel set of jagon that I didn't fully learn in my short time at Boeing!
  - sjwright 12y ago
    > Oddly enough it was Linux on one side and Windows on the other. Doesn't sound at all odd -- quite sensible actually. Though I would probably have suggested a pairing more along the lines of OpenBSD/x64 and Linux/ARM or some-such. It depends on what the remainder of the systems is using. This is a perfect example of where ecosystem diversity is a Good Thing.
empressplay 12y ago
Every map channel I've seen has been analog, even on otherwise purely digital IFE, implying that the map video signal is generated by a device networked on the avionics side and then piped by standard RF to the IFE, like the address system. So no two-way communication.
- kalleboo 12y ago
  Newer ones are digital (I've seen 3D interactive ones on an A380)

gizmo686 12y ago

Probably, although if you were paranoid enough (or required by regulation), you could airgap the TVs and give them information through a normal GPS system (minus the artificial altitude restriction), or have a hardware unidirectional data path. More reasonably, you could consider the TVs part of the flight system network (with many of the same protections to prevent someone from physically opening one and hacking), and still have an airgapped wifi network.

StavrosK 12y ago
What altitude restriction? My phones' GPS works fine in flight, I use it a lot to check speed and altitude.
- klodolph 12y ago
  Yeah, the altitude restrictions don't really apply to commercial flight. You can conduct a test yourself, you just need to get a little higher and travel a little faster than your typical 757. Try attaching your cell phone to a rocket travelling over 1200 mph or above 60,000 feet, you'll find that your GPS unit basically shuts down. That's not to say that your GPS hardware is incapable of operating under those parameters, it's just designed to shut down so it can't be used to guide ICBMs. Commercial airplanes typically operate at half the altitude and speed which would trigger the condition.
  - MichaelApproved 12y ago
    Don't both speed and altitude trigger the block? The gps must be over a certain altitude AND be going faster than a certain speed.
    - callesgg 12y ago
      It is one or the other.
    - proexploit 12y ago
      IIRC, the legal requirement is to shut down with both conditions are present, some GPS manufacturers simply found it easier to implement each restriction separately.
    - michaelt 12y ago
      According to [1] some manufacturers apply this limit when both speed and altitude limits are reached, while other manufacturers disable tracking when only a single limit is reached. The limits are 1,200 mph speed and 18,000 m altitude. Google tells me a 747's limits are around 615 mph and 14,000 m; Concorde's limits were closer to 1,350 mph and 18,300 m. Still, I'm sure if you're making an airliner you can get access to GPS receivers that will work even at maximum speed and altitude! [1] http://en.wikipedia.org/w/index.php?title=CoCom&oldid=608893426#Legacy http://en.wikipedia.org/w/index.php?title=CoCom&oldid=608893...
  - kalleboo 12y ago
    Do the limitations also apply to GLONASS which is now in all modern devices?

sjwright 12y ago

For stuff like positional and airspeed information, it would not be difficult to design a connection that is physically limited to one-way communication. It would also seem sensible that any interaction the pilots might want to perform on the cabin computer systems could be done by giving them a terminal on that network.

com2kid 12y ago
For some stuff that did have data sharing there was a very tightly controlled pipe. Oddly enough it was Linux on one side and Windows on the other. The level of scrutiny that IPC (inter-processor communication) channel got was insane. It is probably one of the safest IPC channels in existence! Unfortunately I didn't fully grasp what systems it was connecting, aviation is full of its own parallel set of jagon that I didn't fully learn in my short time at Boeing!
- sjwright 12y ago
  > Oddly enough it was Linux on one side and Windows on the other. Doesn't sound at all odd -- quite sensible actually. Though I would probably have suggested a pairing more along the lines of OpenBSD/x64 and Linux/ARM or some-such. It depends on what the remainder of the systems is using. This is a perfect example of where ecosystem diversity is a Good Thing.

empressplay 12y ago

Every map channel I've seen has been analog, even on otherwise purely digital IFE, implying that the map video signal is generated by a device networked on the avionics side and then piped by standard RF to the IFE, like the address system. So no two-way communication.

kalleboo 12y ago
Newer ones are digital (I've seen 3D interactive ones on an A380)