Dozy,
Your quote:
Jet airliners have had problems arising from blocked pitot tubes since at least the early '70s and probably earlier (they were central to the Stony Brook NWA 727 disaster, as well as Birgenair 301's B757).
I believe the subject is about Airbus 330/340 sensors and probes that apparently inadvertently fail due to ice/water accumulation or ice blockage at high altitudes. The examples you cite are failures caused by mistakes: Birgenair 301 - B-757 sphecid wasp pitot tube blockage on the ground - Stony Brook NWA B-727 - pilots forgot to activate pitot tube heaters. Hopefully these were not subtle digs at B, but if so, you forgot one: Aeroperu 603 B-757 - static ports blocked by tape that wasn't removed before T/O.
So back to the real thread topic:
Chris Scott Quote:
Reviewing the big picture, it does seem strange that Airbus aircraft have latterly been experiencing so many problems resulting from icing of pitot probes, and now AoA probes. After all, these aeroplanes are operating in a similar environment to other types, and (presumably) jet airliners generally since even I was wearing short trousers.
But I flew the A320 for the first 14 years of its operation, and probe icing didn't seem to be an issue. Were we simply living in blissful ignorance?
and,
Lyman Quote:
The alternative is to look elsewhere. I take note of Captain Scott's troublefree experience in the gen one 320. I have a friend who flew the 320 for ten years, nary a belch or hiccup. What is new that hasn't to do with sensors and heating?
It is my opinion, what Chris and Lyman mention is where the probe and sensor problem rests. The commonality shared with the A330/A-340 is the fuselage that it is different compared to the A-320. If one recalls the aftermath of the AF447 incident, the European certification authorities proposed an update to the pitot probe certification requirements. They asked for comments from manufacturers and users for their proposed requirements. Airbus responded by basically saying the proposed certification standards were not stringent enough and did not reflect what was being experienced relative to high altitude icing conditions. They cited various reasons for this, volume of ice, size of ice crystals, etc. Then curiously they mentioned something important in my mind. The
location of the sensor or probe relative to the
aerodynamics of the
area surrounding these devises was important and was not being considered as part of the certification process. Could it be that the location selected for the probes and sensors on the A-330/A-340 be such that it is more sensitive to ice crystals or water being directed into these devises verses the unshared A-320 fuselage shape or other aircraft where the location may not be as sensitive? Did Thales get a raw deal and bad publicity because their probes happened to be slightly more sensitive than Goodrich probes, both meeting the certification requirements in force at the time because of this? Was the change in the AoA sensor base plate an attempt to fix problems without the need to relocate the sensor location? I am not an aerodynamic or a probe/sensor expert, but as an engineer, I wonder about the relationships here. While it is implied the A-320 has not had the experiences of the A-330/A-340, I wonder what the experiences of Boeing aircraft and pilots has been relative to icing of pitot tubes. Also, the original bill of materials for pitot tubes on the A-330 (perhaps the A-340 as well) were Goodrich pitot tubes, replaced by Thales which were believed better at the time.