It could work along the same lines as the early shared-bandwidth ethernet model:
- Plane, on takeoff and once away from range of the airport (which could be a predetermined value and could even be unique to any given airport) starts listening, and starts a random count to transmit (like the CSMA/CD negotiation for Ethernet). The aircraft is listening for basic data such as grandparent post outlined.
- If aircraft detects a transmission from another, it simply notes the sender ID and checks if it has previous data on that sender. If it does it simply appends to the log on the sender, otherwise it starts a new log with that sender's ID.
- If there's no one transmitting, the aircraft transmits.
- If the aircraft detects a special node, like a ground-based node, and if no one is transmitting, the aircraft transmits its flight history information, and then transmits the collected information on other aircraft. This could be on a different frequency so to avoid interrupting the real-time data from aircraft.
- When the aircraft lands, it uploads all of the history on itself and on other aircraft to the airport. Depending on the airline or nation, it may then delete the logs of other aircraft or it may hold on to them, but it holds on to its own logs until maintenance clears them. Once it takes off, the process repeats itself.
To me this isn't all that difficult of a concept, though it would require mandatory participation among commercial jets to be most effective. It would also require that the system couldn't readily be turned off either, so that a hijacker can't disable it.