There are many articles currently floating across the Internet regarding the search for a missing Malaysian 777 airliner. Data from radar and the associated transponder were the first clues analyzed. In this scheme of things, the ground-based air traffic control (ATC) radar will send out a coded pulse on a each of the system's given azimuths.
The transponder will then reply back with its own coded pulse. This pulse provides added information back to ATC as to the flight's status, including altitude and -- more recently -- GPS coordinates. A significant limitation of the system is that, if the transponder goes offline for any reason, then the ATC radar may not have enough sensitivity to track the aircraft at long range. Also, should the aircraft descend to a lower altitude, the curvature of the Earth may shadow the aircraft somewhat and further limit the detection range. Any of these related scenarios may make the aircraft disappear from radar.
Military radar, such as that mentioned in some of the articles, may be able to track at longer range and sometimes even lower altitude, but it gives no information relating to flight ID, etc.
ACARS (Aircraft Communications Addressing and Reporting System) is a digital datalink system used for the transmission of short, relatively simple messages between aircraft and ground stations via radio or satellite. ACARS will send packets of data to ground-based networks. Should the altitude drop or this system go offline for any reason, then this information stream will cease. SATCOM (satellite communication) relies on satellites and is not affected by altitude. It is, however, very expensive, because multiple satellites are required for global coverage, and even 250,000+ ships and 30,000+ airliners provide a limited market.
Furthermore, the speed of the data over the network can be quite slow if there is significant traffic in a given region, as all the ships and aircraft can potentially be sharing the same spot beam on the satellite. These antenna beams are like a directional spotlight that only illuminates a patch of the Earth's surface. In the case of the Malaysian airliner, it was likely built in the 1990s, and -- depending on whether or not it had been upgraded -- it may share a 128 kbit/s data channel with every ship and plane in the region, in which case the data being transmitted is usually very limited. There are services that offer flight-following via this, however it is an added overhead expense, and if all the ships and planes used it the network would likely be too congested for other traffic.
Information is also pouring in anecdotally about cellphone and instant messenger clients remaining online for days after the flight disappeared. However, unless one of the people on the flight signed up for a service to be tracked via cellular and had this capability turned on, there is little position data given. IP addresses used by the messaging clients may offer some additional clues as to location on the global 3G/4G networks, provided this information propagates across national boundaries.
The bottom line is that, even with the wealth of communications capabilities available to us today, limitations in our technology -- coupled with financial constraints -- are impacting the search for the missing Malaysian 777 Airliner. What is your take on all of this?