12 days ago, 228 lives were abruptly lost when the AirFrance flight 447 from Rio de Janeiro to Paris disappeared in the Atlantic Ocean. My thoughts go at first to the families and relatives of the victims.

Now that the initial mediatic storm is over I want to comment on certain points. This post is based on questions that friends of mine asked. Some are reactions to unclear or partial information heard in the media. This post is about thunderstorms, radar coverage, communication, automated messages, electronic flight instruments and flight controls, pitot tubes, and causality.

Thunderstorms
Thunderstorms are powerful things. Can one destroy an aircraft ? Yes, indeed. Over the Read this older post about thunderstorms for more details. Pilots avoid thunderstorms using the on board weather radar. No crew will ever fly in a thunderstorm without a working weather radar. Beyond lightning and hail, thunderstorms also contains massive quantity of water and icing.

Radar coverage
The exact position of the accident was not known for a simple reason: there is no radar coverage over the ocean. A typical radar has a range of 150 to 200 nautical miles, which is much less than the distance flown over the Atlantic. Even if a radar was installed on each island, many holes would remain.

But what about GPS ? Yes, GPS is global. But remember, GPS is used by the aircraft to determine its position. The GPS system is “one-way”. The satellites are not informed about the position of the receivers.

Communication
Over land and near the coasts, pilots and controllers communicate using VHF radio. This requires direct line of sight between the transmitter and the receiver. The range of such radio is limited because the Earth is not flat.

HF and satellite are working over the ocean but they are not reliable or easy to use. Typically, pilots receive two HF frequencies before crossing the ocean and have to use one or the others, depending the state of the ionosphere. Moreover, proximity with thunderstorms don’t facilitate communication because of electromagnetic perturbations.

Automated messages
The aircraft sent a certain number of messages about failed systems. These messages are transmitted via the ACARS system to the airline’s maintenance unit. They are designed to inform the maintenance teams about the works to be done and help them prepare their intervention. Aircraft are complex systems and almost all flight sends at least one such message. Because of this limited purpose, these messages do not contain the position of the aircraft at the moment the failure occurs.

Electronic flight instruments and flight controls
Airbus aircraft are equipped with computer screens that replace the classical, mechanical instruments and fly by wire systems which interpret pilot inputs and fly the aircraft accordingly. Is this high technology less reliable than “good old” electro-mechanical instruments and direct, hydraulically assisted controls ?

The safety record of Airbus is not bad at all. This A330 is indeed the third being lost within almost fifteen years. Remember that the certification standards are the same for all aircraft, whatever the technology they use. Are such modern aircraft too complex, are they “pieces of engineering” ? These are the classical things heard after each Airbus incident. Once again, the safety record seems to speak against that. Media never report about all the cases where the technology compensated for pilot errors. 80% of recent accidents find their roots in human (not always pilot) error.

Pitot tubes
The pitot tubes are the sensors measuring the speed of the aircraft with respect to the surrounding air. They are tubes pointed in the direction of flight and provide air to a pressure sensor. The pressure generated by forward movement is measured and this is the base for speed measurement. If they get obstructed or damaged, the pilot and flight computers don’t get a correct speed reading anymore. The Airbus 330 is equipped with three pitot tubes.

Loosing all of them is not an enviable situation because the difference between stall speed and overspeed at high altitude is really small. However it the pitch attitude and power setting are maintainted there is no reason the aircarft would depart controlled flight.

Causes and effects
In the present situation, we have very partial information only about what happened via the maintenance messages. A crutial part is missing: which of these messages are causes and which ones are effects. For example, the autopilot was disconnected. Was it because it failed or did the crew disconnect it for some reason ? The black boxes will tell a lot more, if they can be found. Until then, all what will be said will be speculation only.

I hope this post helped you to clarify your thoughts about this accident. Feel free to ask for more via comments.