John M. White posted an interesting article at all-things-aviation.com about black-boxes. The recent crashes of the AirFrance and Yemenia in the Ocean shown that recovering the black-boxes is not always an easy thing and could even reveal impossible. Even if the black boxes are very resistant by design it sometimes happen that they get destroyed in accidents. The investigation work is much harder without the massive data recodring by the black-boxes. As a reminder, there are two black-boxes: one records cockpit sounds and radios and the second records flight and engine parameters.

The AF447 accident raised a lot of questions because of the maintenance messages being sent by the aircraft shortly before the crash. The idea of having an aircraft sending all data per satellite is really seducing but with present bandwidth it’s an illusion. The Cockpit Voice Recoder alone records several radio channels, pilot and co-pilot microphones, and all communication with the cabin-crew. It also recodrs ambient cockpit noise, constantly. This includes clicks of throttles, vocal alarms, beeps and pings… everything. Recording 5 to 10 audio feeds per aircraft in a remote center is not a problem, but taking these feed there is something else. I’m not even sure the present satellite system could handle the load.

The second black-box, the Digital Flight Data Recorder (DFDR) records aircraft and engine parameters at different intervals. This includes control inputs and resulting outputs. Some parameters are recorded several times per second. This is extremely useful for investigators. It’s typically what they use to build reconstitution videos, like this one of Colgan 3407. Transmitting all this data constantly from all aircraft worldwide is simply not possible with today’s technology. At least not over oceanic area.

Even if this was possible, it would raise an interesting legal question. Black-boxes are intended to support investigations and hold only 30 minutes of data. The crew can also erase the voice recordings while on the ground. This is part of privacy protection. If aircraft start to transmit live audio feeds to their home companies, the risk exist that companies start to spy their crews. Not only after incidents, but on a daily basis. No good.

So why not record data on board and send it to the ground shortly before an accident ? This question might seem strange but I heard it a couple of times. The problem is the lack of “accident warning”. Some accidents have some precursor signs. In the AF447 case, the warning about the cabin pressure could have been a serious sign. But some accident are so sudden that there is no warning. Think of the case of a mid-air collision for example. There is simply no warning, apart may be TCAS warnings. But here again, can we afford to send massive burst of data for each TCAS alarm ? Not sure, and not sure we want to, there are so many benign alarms…

Any thoughts to share ? Let’s comment…