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AF 447 Thread No. 12

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AF 447 Thread No. 12

Old 10th Aug 2017, 09:22
  #1581 (permalink)  
Join Date: Nov 1999
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I strongly believe that there should be a stick shaker on every aircraft.

No matter how clever a FBW system might be, the haptic (touch and feel) feedback of a shaking stick/yoke and the unmistakable message it gives you is a fundamental aspect of flying - one that we all learned on day three while learning to fly our Cessna 152's.

Several dozen pages back in this thread I gave an account of when I was given the AF447 scenario in the SIM, without knowing it was coming. Afterwards I said to the trainer "but the 'stall stall' never sounded". The trainer said, "yes it did, it was going all the time".

I simply never heard it - my brain ignored it completely.

Secondly, I think that stall practice should be mandated by the XAA's for every SIM we do. In the SIM we always practice an engine failure on take-off, a single engine (or OEI) approach, a single engine go-around and a single engine landing.

I think a couple of stalls should be added to this list of mandatory items because in modern FBW aircraft, we never experience even an incipient stall, so we forget how to recognise the signs and we lose the correct reflex action to a stall that we should all have.

Last edited by Uplinker; 10th Aug 2017 at 09:33.
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Old 10th Aug 2017, 10:10
  #1582 (permalink)  
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Hi Uplinker.

I agree the stall warning should be "shaker". When the flight deck of AF447 was swamped with visible warnings and a continuous audible "C Chord" altitude deviation warning, I guess their brains filtered out the "C Chord" whist they turned their attention to the other visible messages. When the "Stall Stall" warning replaced the "C Chord" (higher priority) neither crew member commented (they probably didn't notice - like a ticking grandfather clock).

If you examine the flight deck transcript in the 2nd interim report, the "C Chord" was never canceled. It was only interrupted by "Stall Stall" and GPWS "Pull UP".

This U tube video shows how the brain can filter out repetitive audio warnings.
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Old 10th Aug 2017, 22:26
  #1583 (permalink)  
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Stall warning and beating the system

Not sure when Okie flew the Viper, but in the very beginning we were surprised that we could get the rascal into a a deep stall. Regardless of how you got there, the jet would maintain close to wings-level with no serious yaw and nose high unless inverted. Vertical velocity was about like AF447. All this was with fully finctional aero data from the pitot-static systems and the AoA sensors and the rate/gee sensots in the computer boxes.

Unlike the 'bus, our system cut out the stick and rudder once AoA was above 30 degrees. GASP! What could we do? "You can't stall this jet", but we found a way. Sound familiar? We had the Aces II seat. AF447 crew plus many pax did not, but three professionals did not realize they were stalled for almost 4 minutes until St Peter told them.

GD put in the manual pitch override feature and we could "rock" the sucker outta the deep stall, as above 35 or 40 degrees AoA the tail was capable of inducing a nose up pitch movement, but not nose down. So unlike the 'bus system, we could further increase our AoA and the nose would fall thru after a push/pull sequence while coming down at 10,000 feet per minute. Fun huh?

I never got into a deep stall, but came close and what happened was a "airshow" tail slide. Vertical zoom and ran outta speed too quickly or the system to save me. Sucker came back down and flipped over due to gravity and some tail surface aero. Once nose pointed down and AoA under 30 deg, the stick worked and simply reset the warning lights to continue the engagement.

I really think I personally could get the 'bus into the deeply stalled condition using the same profile we had in the Viper. You had to get the nose very high before running outta power. Once the speed decreased significantly faster than your power could hold it and allow the AoA laws to work, so you could get beyond the parameters that all the engineers never thought of or programmed into the computers.

I like the stick buzzer idea, but in the 'bus the feature does not seem to work if IAS is too low, or lost like AF447. And we must remember that the stall is AoA related and not gee or attitude or speed. Sheesh, day one lesson in flight school or with a good pilot as I had first time I ever flew on a joy ride.

Thanks for the rehash of aero stuff and such, OG.
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Old 11th Aug 2017, 00:27
  #1584 (permalink)  
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Neutral Stick

I wrestled for some time trying to understand Bonin's chronic "Aft Stick".
First it was tempting to blame his poor seat position, the inappropriate placement of armrest for the controlling hand, (right arm), or turbulence.

Now, I believe Bonin simply did not allow for the aircraft's AUTOMATIC Nose Up Trim from the THS. Neither did he allow for the Nose UP moment of the fuselage due to full thrust from the engines. At Stall, having lost outboard lift from the wings, the Nose went further up, and he was chasing a stick neutral point that was decidedly forward of neutral as he knew (expected) it to be. Was it the result of startling aerodynamics, design, and lack of Stall training? I believe he descended all the way without adjusting for these factors. This has been in the back of my mind since the wreck was discovered and the final report.

Whatever prompted Bonin's "But I have been holding aft stick for some time..."? I believe whatever possible solution Robert had in mind, Bonin had already thought to try. Why did Robert (emphatically) demand "Climb, Climb, Climb..." After Bonin responds, Commandant demands "NO NO NO, don't climb". Robert may have meant "ascend". Bonin may have heard: "pull, pull......" This exchange is fraught with mystery, and sadness; confusion is so apparent.....

So, the aircraft has just taught Bonin not to recognize the aero at Stall due to its inherent stability, and to misjudge the quadrants of the stick, ("the aircraft cannot Stall"), and the piece de resistance? StallStallStall when forward stick is applied and indicated airspeed exceeds sixty knots... Counterintuitive, poor design, and fatal.

Plenty of room under these circumstances to allow for some retrospective slack in the armchair judgment that is traditional in these threads. At least insofar as the stick is concerned. This is not sympathy nor defense, it is the truth as I see it.

There's more.....

Poor weather brief, "triple redundant ADIRUs" that simultaneously fail due to known but unmitigated design flaws and failure to replace the Pitot components pursuant to regulatory and mandatory orders.

At gums post #1397.... (not that long ago)

"- The jet has really great aero to get into a stall without obvious shaking, buffet, wing rock and so forth."

From my post #1403...


"- The jet has really great aero to get into a stall without obvious shaking, buffet, wing rock and so forth."

I think that is intended as a compliment.... I think it is actually an indictment.

Last edited by Concours77; 11th Aug 2017 at 00:56.
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Old 11th Aug 2017, 09:45
  #1585 (permalink)  
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I agree with you! At our age carping can be a waste of valuable time :-)
I was surprised by your remark on the effect of airspeed decay rate on deterrent buffet level. I think I have read most of the published official and semiofficial papers on AF447 but I don't recall ever seeing that comment. Neither can I think of any aerodynamic reason why it should be so.Anyway, driven by a combination of curiosity, a sleepless night and boredom I did go back to the final BEA AF447 report.
I couldn't find any reference to your remarks in that document, but I did find that they say stall warning was triggered at 02:10:51 and from Fig 67 the computed airspeed at that point was about 216 kts (on a lousy scale!). BEA then concluded that the aircraft reached deterrent buffet at 02:10:57, at which time the computed speed was 211 kts. Given the quality of the graphic that's as near as maybe 1 kt/sec. The deceleration increased after that of course but that is to be expected when the aircraft enters a stall.
At the moment I don't see any reason to change what I wrote, but if you do locate a reference I would be very interested.
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Old 14th Aug 2017, 00:11
  #1586 (permalink)  
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Speed decay versus buffet onset

The buffet in the 'bus most likely manifests itself if you are approaching the "critical" AoA fairly gradually. My VooDoo told me real early, and a degree or so before the "pitch up". My straight wing planes only told me a degree of Aoa before the stall. My swept wing jets other than the F-102 did not have a distinct "break" in the buffet/burble. The Viper had no distinct buffet and simply went onto a deep stall or not, depending upon entry conditions.

All the references to stall and such that use knots or mph or furlongs per fortnight are based upon one gee flight and st-and-level. But Orville taught me that the AoA was what we had to pay attention to. I can take anoyone here up in a Cub or new trainer and show/teach the "feel". If the nugget can't feel the burble, then I recommend going to transports.

Last edited by gums; 14th Aug 2017 at 00:56. Reason: typo's
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Old 14th Aug 2017, 02:21
  #1587 (permalink)  
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Unfortunately Gums, civvie airliners are a sort of "transports" - I guess you catch my drift ...
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Old 14th Aug 2017, 17:19
  #1588 (permalink)  
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Going back to my time in single jets, when I pulled up into a stall turn at well above stalling speed at high g and then relaxed the pull on the stick when nearly vertical. With insufficient power to keep going up the aircraft would start dropping backwards - the aircraft definitely stalled -but at no time was there any pre-stall buffet as at no time was lift being demanded at high AOA.

There can only be buffet from an aerofoil attempting to produce lift at an AOA that results in the airstream breaking away into a turbulent flow. It is the pre-stall turbulent flow that creates the buffet. Pull above your aircraft ceiling in a zoom climb and relax the pressure at just the right time and you can go past the stage where there could be buffet as you are not demanding lift but the aircraft is in a more upward ballistic trajectory slowing all the time. Maintain attitude by putting full power on the underslung engines that cannot provide sufficient lift but will keep the nose well above normal AOA with insufficient power to drive out of the stall. The aircraft is now on the wrong side of the drag curve both wings stalled and the aircraft starts to drop in a nose high attitude. I doubt that at any time that there was any noticeable pre-stall buffet.

A late addition - this way of entering a stalled condition using engines to 'sit on the power' will also not result in a nose drop especially with underslung engines at high thrust and a pilot intent on keeping the wings level. Reducing the thrust or allowing a wing to drop to fall out of the stable stall would have resulted in a nose drop and recovery.

Last edited by Ian W; 14th Aug 2017 at 17:26. Reason: late addition
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Old 14th Aug 2017, 18:22
  #1589 (permalink)  
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I suppose if one performs enough tasks wrong or not at all and doesn't respond soon enough to warnings, even an AOA display can't save the day:


Last edited by Turbine D; 14th Aug 2017 at 18:23. Reason: word correction
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Old 15th Aug 2017, 17:07
  #1590 (permalink)  
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How True

..... or as one wise ex-boss, and very good engineer, once told me, 'this [thing] is fool proof, but it's not bloody fool proof'.
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Old 6th Sep 2017, 21:55
  #1591 (permalink)  
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Endless...but what do you expect when France only spends 1% of its GDP on justice!
Long awaited 3rd technical report by independent panel delayed until 15 October much to the anger of anti-Airbus class action suit.
This time AF is going to be strung up and the writing is on the wall!
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Old 29th Sep 2017, 07:30
  #1592 (permalink)  
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The Camera That Never Lies!

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Old 4th Nov 2017, 19:38
  #1593 (permalink)  
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Old 4th Nov 2017, 19:43
  #1594 (permalink)  
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Are the claims of ?psycho automation? in regard to Qantas flight QF72 justified? | RealKM
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Old 4th Nov 2017, 20:56
  #1595 (permalink)  
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Absent the "psycho" pejorative, 447 did indeed experience a "single event effect". Which one? A rather pedestrian failure of a system touted to be "triple redundant", it was no such thing. Redundancy implies separate (back up) system, or at least, alternate source, not "common failure of three identical sensors....collecting periodically and equally discordant data....resulting in erroneous and NCD output."

Producing a disruption in auto flight, a decay in flight law, and uninterrupted full travel of auto trim to full up pitch.
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Old 8th Nov 2017, 07:10
  #1596 (permalink)  
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Perhaps you can clarify how "A rather pedestrian failure ..." produced "uninterrupted full travel of auto trim to full up pitch." ?

On second thoughts, don't bother.
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Old 25th Nov 2017, 09:02
  #1597 (permalink)  
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Old 11th Jan 2018, 20:18
  #1598 (permalink)  
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Latest official report blames pilots 100%
Crash du Rio-Paris : une nouvelle contre-expertise met en cause les pilotes - Le Parisien
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Old 11th Jan 2018, 20:19
  #1599 (permalink)  
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Old 11th Jan 2018, 21:01
  #1600 (permalink)  
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Posting a link without comment is hardly a worthwhile approach.
I actually found the link you posted to be a thoughtful piece, but I'd be interested to see what about it you consider to be of worth to this particular accident as concerns a professional pilot.
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