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Extract from the Aeroperu Boeing 757 CVR 1996 crash with static vents blocked (English translation)
https://web.archive.org/web/20030427.../183038-1.html One wonders if the Lion Air crew found themselves in the same state of confusion. Sensory overload can overwhelm rational actions every time. |
Originally Posted by D Bru
(Post 10300139)
As concerns the cause, it would seem to me relatively rare for several pitot systems to fail simultaneously. To note that the ias/alt pitot system is separate from the elevator pitot system, the first being located at the front of the A/C, the second on each side of the front base of the V/S. (Repeated) Simultaneous failure of both systems would IMO indicate something more structural then the pitots themselves.
As to the effect, in particular the "FEEL DIFF PRESS LT ILL" could be of particular relevance. The elevator feel computer provides simulated aerodynamic forces using airspeed (from the said elevator pitot system) and stabilizer position. Feel is transmitted to the control columns by the elevator feel and centering unit. To operate the feel system the elevator feel computer uses either hydraulic system A or B pressure, whichever is higher. When either hydraulic system or elevator feel pitot system fails, excessive differential hydraulic pressure is sensed in the elevator feel computer and the FEEL DIFF PRESS light illuminates. I stand to be corrected, but if (barring hydraulic problems) the elevator feel and centering unit enters into a condition that triggers the FEEL DIFF PRESS annunciation (for whatever reason, either pitots or a more systemic failure, since in this case also the "main" pitot system could have been affected simultaneously), it would mean that particularly in manual flight the elevator inputs through the control columns could have a much different (greater) effect than normal. It would be interesting to know whether such inputs with a "dysfunctional" feel and centering unit could lead to upsets with an ultimate loss of control, which at relatively low altitude would be difficult to recover from in time. The FEEL DIFF PRESS light from the elevator feel system is very puzzling because (as you said) the pitot system is separate, and to my knowledge totally isolated from the ports/ADMs/ADIRUs at the front of the aircraft. I am assuming an actual large hydraulic pressure difference between systems A and B would lead to more fault indications than just the FEEL DIFF PRESS. One thing I can't find out is the static source for the elevator feel pitots, but this system should be in an unpressurised part of the plane and hence could just sample it's ambient surrounds to pair with it's pitot. So how could these problems be related? On thing to consider is whether the STS (if operating on bad airspeed data) could effectively contaminate the feel system operation via the changes it makes to the stab trim. Stab trim position is an input to the elevator feel system along with airspeed from it's dedicated pitot system (which should have been working even with issues with the nose airspeed sensing systems). In this case the operation of the STS with bad airspeed is the major issue, with likely alteration of elevator feel a secondary (but likely very unhelpful) issue. |
Do the stats show that the Children of Magenta are crashing planes due to lack of manual flying skills? Are planes crashing on stormy 30 knots cross wind approaches? I would argue that that the pilots who flew AF447, Emirates 521, AA 8501, etc. could fly manual just fine. The problem was that they had no idea what the automation was doing when problems crop up. It's the sheer complexity of modern aircraft. Excellent in increasing air safety to unprecedented levels but has become incredibly complex for both "old school" and "magenta" drivers.
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AF447, Emirates 521, AA 8501, etc. could fly manual just fine. The problem was that they had no idea what the automation was doing when problems crop up. Isn't the point that if " they had no idea what the automation was doing" then they should hand fly? As you say "they could fly manual just fine". I agree it is not too difficult to occasionally "get lost" in the automation modes, that is why there are disconnect buttons. |
If a pitot cover had been left on it should have been very obvious to the crew before they even got to 80kts on the take-off roll, surely?
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"I would argue that that the pilots who flew AF447, Emirates 521, AA 8501, etc. could fly manual just fine."
The fact that these perfectly flyable aircraft crashed voids your statement. |
Thanks for setting me straight you guys. No, I don't deal with airliners, but I learned a lot following the entire, sorry AF447 thread! Sorry for my ignorant remarks, I meant well.
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Originally Posted by FL11967
I would argue that that the pilots who flew AF447, Emirates 521, AA 8501, etc. could fly manual just fine.
Originally Posted by 1624
The fact that these perfectly flyable aircraft crashed voids your statement.
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Originally Posted by 1624The fact that these perfectly flyable aircraft crashed voids your statement. That was my point. |
Originally Posted by parabellum
(Post 10300979)
If a pitot cover had been left on it should have been very obvious to the crew before they even got to 80kts on the take-off roll, surely?
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If a pitot cover had been left on it should have been very obvious to the crew before they even got to 80kts on the take-off roll, surely? Which of course begs the questions...100 knots check? V1 Rotate? The crew acknowledged they had red SPEED flags on their PFD. https://www.atsb.gov.au/publications...r/ao-2018-053/ |
A summary of ATC discussions was posted on Tempo. My translation of what was published as follows.
06:21:23 Pilot made first contact with ATC. [Altitude 900ft] 06:21.53 Pilot reported flight control problems and asked for holding position at 5000ft. ATC gave permission. 06:22:57 Pilot asked the speed of the aircraft from ATC. ATC responded 332knots. (Note: no mention of ground or air speed, the bahasa is "speed of the aircraft") 06:29:39 Recorded data that the aircraft left 5000 feet. (Note: It isn't clear whether this is ATC comms or just an observation) 06:29.55 Pilot given permission to return to arrival using runway 25 because of the flight control problem. 06:31:35 Pilot requested return to point ESALA because of weather and not sure about the altitude of the aircraft. Pilot requested 3000ft clearance with other aircraft. 06:32:00 ATC asked whether the pilot was ready to return to the runway. There was no response. 06:33.30 ATC contacted Batik Air 6401 to look for the position of Lion Air. |
FAMO;
The bahasa actually says he requested the "speed of the aircraft" (kecapataan pesawat). Not airspeed nor ground speed. |
The crew reported 'flight control problems'.
They also asked for a speed from ATC. Then crashed the aircraft in VMC in what appears to have been a high energy dive. Looking at the Tech Log, pitot static snag and 'feel diff' snag. Anyone here ever flown a 737 without the feel diff working? The controls are extremely sensitive, especially at high speed, very easy to overcontrol. 737s tuck easily, and this will get out of the box quick. Gums I agree, we're probably looking at a structural failure, caused by over controlling due to feel diff failure, caused by pitot static problems. |
Which of course begs the questions...100 knots check? V1 Rotate? The crew acknowledged they had red SPEED flags on their PFD. |
Originally Posted by AfricanSkies
(Post 10301005)
Looking at the Tech Log, pitot static snag and 'feel di Anyone here ever flown a 737 without the feel diff working? The controls are extremely sensitive, especially at high speed, very easy to overcontrol. 737s tuck easily, and this will get out of the box quick. Gums I agree, we're probably looking at a structural failure, caused by over controlling due to feel diff failure, caused by pitot static problems. There is a lot of talk about pitot gives giving incorrect readings but this still does not explain why it dropped like a rock in VMC. There would have been some form of correction on the way down. |
Originally Posted by AfricanSkies
(Post 10301005)
The crew reported 'flight control problems'.
They also asked for a speed from ATC. Then crashed the aircraft in VMC in what appears to have been a high energy dive. Looking at the Tech Log, pitot static snag and 'feel diff' snag. Anyone here ever flown a 737 without the feel diff working? The controls are extremely sensitive, especially at high speed, very easy to overcontrol. 737s tuck easily, and this will get out of the box quick. Gums I agree, we're probably looking at a structural failure, caused by over controlling due to feel diff failure, caused by pitot static problems. It’s a good point though, if they did lose elev feel, it possibly could lead to LOC or structural damage if not managed carefully. I am surprised, however, that a fault with main air data could also cause a feel diff press problem. I thought they were essentially independent. I only fly NG, not MAX. So this is an interesting malfunction (the previous flight). |
Anyone here ever flown a 737 without the feel diff working? The controls are extremely sensitive, especially at high speed, very easy to overcontrol. When you say “ without the feel diff working”, do you mean without the elevator feel computer working? Cheers |
Great advice given to me while flying the ERJ-145 many years ago, was to simply put the N1 needles to 12 O'clock if you are unsure of airspeed.
this gave a power setting that was pretty unlikely to induce an overspeed, but was enough to avert a stall as long as you flew roughly level. The thing would bumble along at about 200 knots if I remember correctly. I think all aircraft could this sort of general advice, but I can also think of a few reasons why I've never seen it written down. |
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