Overnight the Wall Street Journal reported (paywall) that the Boeing 777 flying as Malaysia Airlines 370 was transmitting data about its location for five hours after its transponders stopped functioning and it disappeared from normal Air Traffic Control coverage. Thus the forensic mystery I mentioned last night -- that there was no evidence that the plane did keep flying, and no evidence that it didn't -- is clarified. It leaves the disturbing mystery of why and where the plane would have been flying incognito.
This is my Annie Hall/ Marshall McLuhan moment for discussing the topic. At the moment I am sitting aboard a United Airbus A320, which (a) is equipped with WiFi, the third such WiFi moment I've ever had in my thousands of hours and millions of miles on United over the years, and where (b) I am sitting next to a dead-heading United pilot, who is telling me what he has learned and thought about Malaysia 370.
Here are several reactions from readers in light of the overnight news. They began with references to the expert I quoted yesterday, Michael Planey, who argued that there would be no point in requiring live-streaming of "black box" data.
Executive summary before we go further: This latest information obviously works against possibilities that the plane vanished from radar coverage because it blew up -- via bomb, some structural failure, missile strike, meteorite, what have you. The fact that the plane kept flying, with its transponders turned off, also works against any "pilot hypoxia" assumptions. (The idea that the pilots somehow both lost their oxygen supply and passed out, as happened in different circumstances 15 years ago in the Payne Stewart crash and in a crash in Greece in 2005.) If two pilots were simultaneously nodding off at the controls, there is no reason why their last conscious act would be to disable the transponders -- rather than radioing for help, descending into thicker air, reaching for the emergency oxygen bottles, etc. Possibilities involving deliberate destruction -- by the flight crew on its own, or by attackers who got control of the plane -- thus become more likely.
Now, the details. I am erring on the side of leaving in all the arcana, since cases like this often turn on precise interpretation of specifics.
1) On how the whole reporting system works. Reader John Shepley, who has experience in the data-reporting business, writes in to say:
Mr. Planey's analysis is mostly correct, but it was written before the knowledge we now have - that the plane did have electrical power as indicated by the registration 'pings' that the ACARS transmitter periodically sent to the satellites, even though the transmissions did not contain any data. (The operation is similar to the way that cell phones periodically transmit a registration signal to the nearest cell tower, even if the user is not using the phone at the time. That's how inbound calls can find the mobile phone.)
The satellite transceiver, such as the Rockwell Collins SAT-2100 is a metal box that sits in an avionics bay - not accessible from the cockpit. It receives the information that it transmits over a data bus from a control unit that is a similar box. A panel in the cockpit provides control functions, allows the pilots to tune the various radios and manages the many functions that the system performs.
A typical system looks like this:
It's likely that there is no power switch in the cockpit for the Satellite Radio or the VHF datalink radios.As seen in the diagram the CMU-9000 boc collects the data fro the GPS and other sensors and formats that data and sends it to the selected transmitter(s).
Commercial airliners don't typically carry HF radios which have a very long range, and are used mostly for polar regions. The VHF data radios would have an antenna on both the top and the bottom side of the aircraft, allowing line-of-sight transmissions even of the plane is in a steep bank or dive. The satellite radios would have an antenna on the roof of the aircraft that would certainly lose coverage if the plane were in a very steep bank or dive. While cockpit-accessible devices such as the transponder and messaging / control unit have power switches and can be turned off, the out-of-the way boxes are probably powered up whenever the aircraft's engines are running..
The voice recorders can provide more information than just the conversations in the cockpit. Several audio streams are recorded: One each from the pilot's and first officer's headset microphone, one or more wide field microphones that would pick up the ambient noise in the cockpit, and any radio or intercom communications. The ambient sounds can be particularly useful and can be used to determine an approximate origin of a loud noise. For example, if an engine compressor exploded in the right-side engine, the sound would reach the first officer's microphone a tiny bit sooner than it would reach the captain's microphone. These sounds and the subtle differences as recorded by each microphone can be analyzed and provide useful clues to events on the aircraft.
Given that we now know that the satellite radio did periodically ping the satellites and therefore, the plane continued flying for 4 hours, my bet is on the idea that someone took control of the cockpit and turned off the transponder and other cockpit equipment.