Symmetrical Located Probes
Hi Lyman,
In regards to the symmetrical located AoA sensors, 1 & 2, if they simultaneously lock up then #3 (the odd man out) is disregarded by the system logic, correct? The same would be true of the pitot probes 1 & 2, again, correct? It seems to me there was a photo of the sensors and probes on the A330 in the AF447 thread that depicted their location near the nose and before the nose blending into the fuselage shape. But, on the A320, the AoA sensors, 1 & 2 are located much farther back, rearward of the forward doors.
If you recall the A320 Perpignan accident, the AoA sensors, 1 & 2 locked up simultaneously at high altitude at a cruise angle. However, the cause was the sensors not being covered during a high pressure water cleaning operation (a procedural error) and they took on water internally (bearing area) prior to the final detail painting step. The plane sat for three days prior to the test flight and during the flight they did simultaneously freeze at altitude unbeknownst to the pilots. The AoA sensors are not designed to be waterproof, neither the Goodrich or the Thales. The certification details are given in the BEA final report.
IMO, the location of the AoA symmetrically located sensors on the A320 would not be subject to as much pounding water as would the A330 AoA sensors because of their location. In other words, the problem with the AOA sensors on the A330/A340 may be associated with water intake based on location and the new conical added plate, not ice crystal formation at altitude.