STALL WARNING
Quote:
Excerpt from BEA - 3 August 2011 ...
Finally, it should be noted that the warning sounded uninterruptedly for 54 seconds after the beginning of the stall, without provoking any appropriate reaction from the crew.
That statement can not be misconstrued. The crew never acknowledged the Stall Warning. The exception could be that they reacted to it inappropriately once stalled.
PEI_3721:
As much as new designs might enhance the salience of a warning, if the crew’s mental model has rejected the warning as being false, inappropriate, or unwarranted in the situation as perceived, then enhancement is of little point.
Remember ‘shut up gringo’ ?
Some other aircraft have, and for good reason, a stick shaker and stick pusher.
Now an electronic version of that sounds very simple, particularly if it repositions trim. However, remember that a ‘rush’ makes for poor law – similarly quick system changes and redesign might have pitfalls elsewhere.
Thus, let the designers think through their system; they probably evaluated such an option in the initial design - certification case to show why it is not required.
Finally all parties must ensure that any change fixes the problem, but do we actually know what the problem is, except perhaps human limitations in perception and understanding.
I am quite familiar with both stick-shaker and stick-pusher, however I suspect you are not really accepting that the system designers have generally NOT considered the region deep into a stall. Certification tests are carried out up to and
approaching a stall, but never stalled. Trying that in a large transport category aircraft is not recommended or tested (except perhaps using computer modeling).
The stall warning systems currently on the aircraft are therefore designed as preventative devices - i.e. if you are hearing this, then things are starting to go wrong, so perform the appropriate actions.
Consider whether, in the normal course of aircraft operation, it seems likely that an aircraft would be *flying* with an IAS of 60knots and a stall-value AoA? Such a realm is easy for the armchair quarter-back to criticize... "why shut off the stall warning when the IAS drops below 60 knots" ---> because such a condition was/is inconceivable for 'normal aircraft operations'.
But my suggestion a page or so posts back now, was to introduce a new warning, not just an aural, but a bloody great block of text flashed across all glass displays in the cockpit every 5 seconds or so, suppressing all other warnings that may or may not be going off. "AIRCRAFT STALLED, AIRCRAFT STALLED, REDUCE AoA!"
As some other contributor noted, it's not very helpful hearing a "pull-up, pull-up" warning if you're fighting a stalled aircraft - if you're stalled with an AoA of 60+ degrees and vertical speed of -10kft/min then it would certainly not help much now would it?
In the Buffalo crash the pilot pulled
through the stick-shaker, but in that case there were issues that were arguably deeply rooted at a skill level.
A simple question:
Would something per my suggestion - "AIRCRAFT STALLED, REDUCE AoA!" flashed in red text on the glass displays have alerted the AF447 crew that they were stalled? - triggered from AoA and V/S?
There are two possible answers - "NO" and "MAYBE" - if it is the latter then proceed with a human factors study, etc. I am not proposing a rushed introduction.
My personal opinion is we, as humans, are bombarded with technology today, but look at the trending.... we are moving away from email to Facebook, and T w i tter (with a limit of 140 characters per message), we TXT msg each other in short-hand code, our attention span is shrinking. When things go wrong we tunnel vision, shutting down our senses - therefore at moments of critical decision making we NEED the available technology to prioritize our input stream for us.