Hi Graybeard,
Originally Posted by Graybeard
The info as presented tries to pack too much into a page, mixing pitot and static pressures together.
AFAIK, all the prior events were airspeed errors alone, and did not have altitude errors.
Whilch prior events? Those before Dec. 1999?
Altitude errors are also recorded with pitot issues: variations are not in the same range but still, erroneous altitude will be displayed.
Originally Posted by Graybeard
Airspeed and altitude are separate and unique functions within the ADR, except at low speeds, and their output data bus words are separate and unique. An ADR may flag or put out erroneous airspeed without affecting altitude output.
Each ADIRU module is separated in two: ADR+IR. If you are turning OFF the faulty ADR part because of unreliable airspeed, you will also reject all the associated static and AoA probes. Hence, if all three are rejected, you are only left with your standby instruments.
Originally Posted by Graybeard
The FCOM Bulletin #009 page 3 gives the case for total pitot obstruction, not just drain hole obstruction, although it is known that Thales pitot were prone to drain hole obstruction due to roughness in the holes. Drain hole obstruction without impact air obstruction will give an erroneous higher than correct airspeed.
What is your source for this so-called defective "Thales" probes? Thales C16195AA (know as SEXTANT Av.) were first issued in order to replace the previously "known" clearly defective Rosemount 0851GR (now Goodrich) which was mounted on the first batches of A330. Goodrich developped the 0851HL for fixing the same issue and Thales the C16195BA for improving the C16195AA due to water ingestion (not ice). At the end, this Goodrich 0851HL is now considered to be the more robust to severe icing conditions.
Originally Posted by Graybeard
Total pitot obstruction, per page 3, puts the plane into an unstable situation. Increase of altitude cause increase of IAS. The A/P will try to increase pitch to reduce the IAS, causing even higher erroneous IAS. This is in accordance with Der Spiegel story.
Except the fact that those airspeed discrepancies were obviously correctly monitored by the system, and that would be not very likely otherwise. In your scenario, no ADR DISAGREE would be triggered - the system being "fooled" by undetected probes issues. In AF 447 case, it appears that the system was not "fooled" and what happened was 3 ADRs finally rejected for displaying unreliable airspeed. Get it?