Originally Posted by
jcjeant
Hi,
Why they will learn now .. when they don't learn before ??
What was there to learn before that we/they didn't already know (then)?
- Sensors can fail (especially if damaged in maintenance) - already known.
- Water in AOA sensors can damage them - known, but maybe to be sure, we should ensure that they are to be covered in washing procedures (oh, already done). Note that we also already knew that remembering to tape sensors up, but forgetting to untape them is also fatal, and that these sort of maintenance failures affect both FBW and non-FBW aircraft. Fatally.
- Triple-redundant system cannot cope with multiple sensor failure - known mathematical fact (see previous discussion on thread).
- Alpha prot will not activate correctly in the event of multiple AOA sensor failure - known consequence of above. By design (and cannot be designed any other way).
- Sensor failure can be identified by both a check flight and "maintenance records" - believe this is exactly as designed.
- Aircraft will fail the alpha prot test on check flight in the event of multiple AOA sensor failure - as designed.
- The failed test will not have any other consequence for test flight (not even a stall warning) - which is as per the design of the test procedure.
All these are still known, still valid - even the last one. In this case the crew conducted a
different and far more
dangerous test in which the inevitable consequence of a failed test was a stall (or approach to) with trim up, which it appears they did not know how to recover. In the light of the latter point, the inevitable consequence of a failed test was a crash.
Why test a protection system whilst relying on it to save you ? - better to not test it at all and hope it works, you'll live longer (on average, whether it works or not).
Maybe we should issue a new procedure that says "for test flights, follow the test procedure, it's really important" (and same for maintenance). Will that fix the issue of people not following the procedure ? Will they learn when they didn't before ?
Finally, on learning, the fatal LOC, the final hole in the cheese, was failure to control pitch / trim, in (approach-to) stall. When will we learn that this issue is
not a FBW issue ?
Quoting the AAIB (regarding the 737):
Safety Recommendation 2009-045: It is recommended that Boeing clarify the wording of the approach to stall recovery Quick Reference Handbook Non normal Manoeuvres to ensure that pilots are aware that trimming forward may be required to enhance pitch control authority.
This isn't the only other incident either. There will be more if people don't learn, and mis-characterising it as a FBW issue
may stop people learning.