Hello jd_ee
You've been quite a prolific poster today.
Your reply has triggered more thoughts, and comments here:
Originally Posted by
JD-EE
Airtren, IMAO the plane's software declares stalls inappropriately.
The problem with the Stall Warning, which I've already mentioned, can be split, IMO, in two parts, each part being a problem on its own.
These may not look as problems to those people that are inside the box, engineers or pilots that were educated/trained to accept the SW, think of it, use/operate with it, as it is.
From outside of the box though, the Stall Warning looks unreliable, and incomplete, to say the least.
First it is the limited number of parameters used for calculation and triggering the Stall Warning, and the high risk of having major parameters, and thus the calculations invalided by adverse weather, inducing a total failure of the Stall Warning.
Second is the single Stall Warning message in itself.
There seem to be
3 types of distinct Stall related situations.
1. Entry/approach to Stall (transition from NON STALL to STALL, or entering the Stall ZONE)
2. Stall per see (Stall, or Stable STALL, or in the middle of Stall Zone)
3. Exit Stall. (transition from STALL to NON STALL, or exiting the Stall Zone)
The current
one Stall Warning message seem to be designed to apply for both situation #1 and #2, but not for situation #3.
In the case of AF 447, the Stall Warning didn't work for any of the situations it was designed for, which is #1, and #2, but it was triggered for situation #3, in which case its interpretation as #1, or #2 was misleading, making the PF think that his actions were wrong, inducing a Stall, when in fact, his actions were in the right direction.
So:
The first problem can be addressed, by extending the number of parameters/sensors, with parameters/sensors that cannot fail, and become invalid at the same time with the others, under the same conditions, so to reduce the risk of failure, and increase redundancy. This also implies a change of the algorithms, and perhaps have several parallel ones, for calculating the Stall conditions.
The second problem, is ideally resolved by adding two more Stall messages, and creating a distinction, so there would be one message for each of the 3 situations, which would make each of them clear, and unambiguous.
1. Warning!!! A/C Entering Stall
2. Emergency!!! A/C is in Stall
3. Information!!! A/C Exiting Stall
Originally Posted by jd_ee
What I really want to know is
WHY the PF might have might have made this apparently inappropriate action.
….Once PF had the plane at 16 degrees pitch and an AoA of 60 degrees I am reasonably convinced it was all over. There was not enough altitude to get the plane back into a flight configuration based on the NASA curves posted here in the past.
… PF needed something to beat into his brain (a physical slap in the face?) to convince him he was stalled.
Based on the division of the time from the AF 447 A/P and A/THR disconnect to the final impact to the Ocean, in two major steps:
1. Transition from Normal to STALL.
2. Attempts to exit Stall, and return to Normal.
On Step 1, based on the current BEA report, I perceive a confluence of causes.
IMO, a PF/PNF failure alone cannot stand, as it has immediately great, and grave implications on Air France, as well as the industry. The Captain and two pilots were employed, were trained, were accredited, and they were tasked to fly the plane by Air France according to its standards, Airbus, and the industry's international standards.
The second step, is not easier to judge. But among all of the failures, one of its contributors is the Stall Warning, i.e. not having it when it was needed, and then having it at the wrong time, with the wrong meaning for the actions of the PF at the time.