AircraftNews.Com

Here at the AN we do not know what causes accidents, or even death for that matter. We leave that to the experts. It does appear that victims advised by their lawyers have ventured there, and now read this:
You may need a web page translator to render French to English.

AF447: The crash of Paris-Rio was avoidable

The Union of Airfrance Pilots(SPAF) say in this report, it is the failure of the Pitot probes to measure speed that caused the crash.

Suddenly AF447 is back in the limelight. This will not go away, lawyers are on the case. The Black Box will probably not be found, but if it were ever to be found many anticipate it would simply elucidate the sequence. At some point the ADIRU gave up resulting in a handover to the pilots in impossible conditions.

Nobody knows exactly what happened to AF447 but what we do know is that airspeed measurement is of critical importance when we are flying at great altitude in subsonic airframes. In pilot slang, as you ascend you enter the coffin corner, the apex of which is a point where the aircraft is stalled and exceeding the speed of sound (MACH 1)
simultaneously, hence the name.

Coffin Corner (Wikipedia)

Here is a simplified graphic of coffin corner courtesy of Wikipedia. With increasing altitude the stall speed increases and the speed of sound decreases. Our long distance RPT jets spend a large percentage of their flight times in the vicinity of this no go point. The fact that jet travel is very safe is testament to the skills of the engineers, scientists and pilots who make all this viable.

Those of us that fly are well familiar with the airspeed pitot system, in fact most of us can tell a story about what went wrong. Insects, dust, ice, covers left on, paint, masking tape, and so on. There have been major RPT catastrophies outside of the coffin corner for these simple reasons. Shit happens, we all know that. The difference with coffin corner is that we are high and fast, a long way from home with poor or no visual reference, and in addition we are stalling or breaking up, all mediated and filtered by a computer which says over to you.

In the great Echo-Chamber of the Internet you will read that we are depending upon the 18th. century technology of Henri Pitot to measure airspeed. In fact there has been a steady development from the time of Darcy in the 19th. century until now. We are committed to subsonic flight for long range RPT, but this pneumatic sensor technology may have hit it’s use by date.

In the very early days the pioneers flew without air speed instruments. The Wrights used a crude angle of attack indicator, Bleriot flew the English Channel with no airspeed instrument. The onset of WW1 encouraged the development of the Pitot-Darcy pitot method of differential air pressure devices to measure air speed in support of the fast and high powered aircraft required to fight a war. The highly developed devices in use today are direct descendents. Essentially they tap ambient air using pitot probes and static ports, measure the pressure difference, then compute and display a calibrated airspeed.

Airspeed measurement technology is in the headlines now, for everybody, not just the aviation buffs.