Hi Geoff,
You've got no answer as new post from new posters do not show up until a while and may be left unoticed. You did bring in a valid point:
Originally Posted by geoff sutherland
The second BEA interim report into AF447, (p62-67), identified 32 other incidents caused by or related to freezing of pitots on A330-A340 and also stated that the test/certification regime (JAR25) for those pitots was for a maximum altitude of 30,000ft.
Why is it that one of the most heavily regulated industries in the world allows almost all of its commercial operations to be conducted using a critical speed sensing technology that is neither tested nor certified for critical icing factors at the very altitude that almost all of their commercial flights are conducted.
Maybe they should limit all flights to within the certified envelope (30,000ft) and wait for the business out-cry to put funds into solving the problem
It is hard to make a very simple answer to this point as this is a very complex issue. I have read few papers on the subject and this may be summarized like that:
- Until not so long ago, about 10 years, most scientists thought that no ice/water particules of any dangerous size for aircraft sensors could be encountered at altitudes above 30,000 ft due to very low atmospheric temperature. There was several long haul airliner pilots testimony saying otherwise during specific flight conditions: oceanic flight over seasonal tropical thunderstorms or at proximity of them. The problem was that it could not be reproduced in laboratory. It has to be 1) to prove the phenomenon, 2) to develop some new probe certification process.
- In fact, almost all pitot events are taking place at lower altitudes on every model of pitots, causing a lot of accidents, mostly in general aviation. Airliners are supposed to be safe due to the constant care about this known issue as well as by multiplying their sensors and backup systems. But the risk still remain that those systems could be overwhelmed by conditions not reproductibles due to actual knowledge and experimental means. It is just not possible to take a sample of one particular atmosphere and to bring it into our labs without changing it. Conditions have to be re-engineered and this seems to be the core of the problem.
- Until AF447, known pitot issues encountered in A330-340 fleet (only) lasted from 5 to 20 seconds. After AF447, other incidents occured, including the other probe models considered less sensitive than Thales AA (Thales BA & Goodrich/Rosemount probes). Actually, it seems that the probe makers are working empirically on this issue, without exactly knowing what to change in order to fix the problem, and it is the same for the regulator. Nowaday, a lot of ressources seems to be affected in order to study very seriously this phenomenon. Some scientists are pointing that it may be caused by climate changes and that it is much more frequent, others that it always existed and was dismissed, but as traffic increased, its frequency increased.
S~
Olivier