I travel frequently across the north sea, between Scandinavia and Iceland. This is a 3 hour flight I generally do in coach. A while ago i started thinking of the good old days, when the vikings travelled this distance as well. Lets compare

Option 1: Longboat
Duration: Several weeks
Onboard meal service: Dried fish, mead, old water
Comfort level: Cold, freezing, wet, damp, salty and sea sickness.
Entertainment: Rowing!
Restroom: "Overboard"
Risks: Likely to die from sickness, fall overboard, freeze to death or get beaten up by a fellow traveller (everyone is armed!)
On-time arrival: Not applicable

Option 2: 757-200 in Coach
Duration: 3 hours
Onboard meal service: Light snacks and drinks complimentary. Warm dishes for purchase
Comfort level: Leather seats, personal cooling available, good temperature.
Entertainment: Loads of videos
Restroom: Complimentary
Risks: Extremely unlikely to plummet into the ocean. Unlikely to get beaten up by a fellow traveller (noone is armed)
On-time arrival: 90%+. Sporadic 1 day delays due to Eyjafjallajökull

I thought of this for a moment, then sat down and enjoyed my private leather seat and in-flight entertainment in "coach".

Well put. Prices have gone down drastically because of a number of factors.
* Less space per pax
* Better aircraft and engine
* Better utilization of aircraft
* Reduced service (drinks+meals moved to paid ancillaries)

Todays "coach" class really is no more than a bus. If you want comfort, upgrade. Else, suffer in silence :-)

Hekla is harly a major issue. She has erupted 5 or so times in the last 60 years with small amounts of ash and lava. She has no glacier on top of her.

Or "Snakes on a Plane". Which for some strange reason never made it to the inflight entertainment systems :-(

The article isn't very clear on exactly what they managed to do, but it is quite possible that there is a shared satellite data communication system shared for infotainment systems and aircraft system status/updates/notifications alike. Hopefully with a robust QoS in place. So _if_ someone could break into the message routing, they could intercept and possibly create their own messages to send along the channel.

If you check TFA's quote:

Since a modern airline has lots of avionics communicating with the ground, it could be that some of those messages may be edited/interrupted/faked. That's not to say that you could rlogin to the FMS and alter flightplans, or alter the flight path in any way.

More and more aircraft and ATC centers support ADS-B transponders and data, which include a GPS-derived position (altitude + position) messages as a part of System Tracking (you can check out Eurocontrols Asterix cat62 protocol and ADS-B applications). Older MSSR radars will provide you with a rough estimate of the position and an assumed altitude based on the aircrafts built-in systems, which is being tracked using for example Kalman filters to predict the current and future position. Switching over to GPS as the primary source of positioning data is allowing tighter packing of aircraft (reduced horizontal and vertical separation rules), which is becoming critical for congested airports to reduce the time between takeoffs/landings, as well as to keep aircraft in holding patters packed tighter together.

Also, ADS-B can be sent as frequently as 1 message/second due to signals going down towards earth rather than in all directions. Current MSSR radars usually have a scan time of 5-12 seconds.

So interruptions with these data links (say someone hacks into it and manages to shut it down) would lead to the ATC center having to fall back on MSSR Tracking, meaning you will be violating horizontal and vertical separation rules until the controller can create more space around the aircraft again.

The pilot can use these data link communication channels to make his/her life easier. As an example, when asking for a new flight level clearance, they can (given up2date Flight Management System computers) dispatch a digital message to ATC (Air Traffic Control) rather than using the radio. A bit like sending a text message. This can be far more reliable than long-range radio where the audio quality isn't great. Similarly, the ATC can confirm the flight level clearance (climb or descent) via a data message, rather than over radio. The FMS display will confirm, reject or propose alternatives.

I can imagine a couple of not so scary scenarios:
* Overloading the data link, causing other messages to be delayed and/or dropped. This means the pilot will have to fall back to radio and/or resend the message.
* Read in-flight reporting/confirmation data
* Read load manifests, fuel status updates, passenger manifests etc.
* Access what other passengers are watching on their inflight entertainment system
* Eavesdrop on other passengers' facebook chats

And some more scary ones (if the break-in allows access to flight data messages):
* Send/request ATC communication, clearance requests etc
* Flooding ATC stations/comms systems with bogus data, preventing efficient communication between aircraft (this, and others) and ATC

One would assume the fly-by-wire system is entirely isolated from this.