Originally Posted by
jcjeant
Obviously when it will be talks of Airbus at the trial .. discussions on behavior and the system of THS going to be warm while it operated in accordance with the specifications
Autotrim is a damned if you do damned if you don't scenario. If its purpose and accepted effect is to reduce pilot workload in normal flight, then the corollary is that turning it off will _increase_ pilot workload, and turning it off in an emergency when pilot workload is already increased will...
I hope any discussion will include whether or not turning autotrim _off_ was the "right" thing for the system to do in incidents such as G-THOF and D-AXLA, where the pilots needed to trim manually and did not do so. It should also include other similar incidents e.g.:
"At the moment the stall warning activated, the horizontal stabilizer trim began to increase its pitch-up action in a progressive manner until it reached the pitch-up stop."
- Name that type, and why did the trim go up ?
It would be good if the discussion included not just the specifications but the certification requirements and the behaviour of other a/c / mfrs in similar circumstances if the requirements are not tightly specified.
The Boeing engineers' comments (sorry, I lost the link) regarding FLCH "trap" are also worth raising. They knew about and discussed the exact scenario that later planted a 777 onto a sea wall, and whether or not the system should override the pilot commands. In the end, Boeing chose to go with their central philosophy - that the pilots must have the final say in controlling the plane. After decades of censure from some quarters over its implementation of hard-protections overriding the pilot, would it not be ironic if AB were to be censured in this case for a mode where (due to bad sensor inputs) its plane acted like a Boeing and slavishly followed the pilot commands all the way to the sea / sea-wall ?
The STALL alarm system and behavior will certainly be put on the grill also
I would hope we find out what the "modifications" to the SWC that were alleged earlier in this thread actually are, and how they impact the false alarm probability and the possible impact on _perceived_ false alarm probability. Is it not a reasonable conjecture that 447 crew believed the stall alarm was false, especially given the BEA note that other UAS crews ignored stall alarms believing them to be false (no one seems to have investigated _why_ they thought they were false - or at least it isn't in the report) ?
If the certification standards don't specify SW behaviour in absence of AoA data, I would want to know what other types/mfrs do - alarm or not - before attaching blame to AB. Similarly on the air data unit (not, I think, by AB, and maybe used elsewhere) that invalidated AoA data in the first place. Also relevant is why AF rejected the BUSS option - on cost ?