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Popping in from lurking, will be gone in just a sec.
Ranger One and Aluminium Shuffler Talking to the airplane would make sense in a way. I am totally talking to my car sometimes - confusing as it is to my passengers, LOL! Y'all What do you make of the strange bump in mommaklee's data? Gusts/drafts/the wrath of Mammon? Some kind of mishandling? Or just FR24 junk data? |
Not quite.The autopilot trim system also runs at two speeds ( high or low) depending on the flap position. Well sort of. The high speed AP trim though is equal to the manuel electric trim speed with flaps up. The AP flaps up trim speed slower still. From Boeing: Normal electric trimming of the stabilizer is done at one of two rates as controlled by flap position. Trim rate with flaps retracted is 1/3 the trim rate with flaps extended. The autopilot actuator also trims at one of two rates as controlled by flap position. High speed autopilot rate is equal to the normal electric low speed rate. The low speed autopilot rate is 1/2 the rate of the high speed autopilot rate. |
This accident is strikingly similar to the Tatarstan Airlines Flight 363 B735 that crashed at Kazan, Russia in 2013. This is the graphic of the vertical profile in that accident: One possible reason for this profile is something I have seen in light aviation training - a confusion between stalling and zero g. If the push results in reduced g or slightly negative g, it can be percieved as the aircraft stalling, and so pic continues to push forwards to 'unstall' the aircraft. And the result is similar to that profile. And this is not something that all pilots have trained for, as aerobatics are not on the syllabus. And is not something you can train for in the simulator. And there is a big difference in individual responses to odd attitudes and zero g. Some students shout 'yeeeehaaa' and ask to do it again, while others freeze. And it is not always the bold and confident student who shouts 'yeeehaa'. But if the reaction to zero-g has never been addressed and mitigated back in flight school, it is never going to be so in commercial flying. (Especially with spinning off the syllabus now.) This is where a post-CPL course is aerobatics and gliding would be beneficial to all new candidates, to stretch their horizons and abilities. Experiencing an upset for the first time with pax on board is not the best time to discover you are uncomfortable with the sensation, or don't have an automatic stall identification and response reflex (Air France please note). |
Originally Posted by mommakee
Also, for what it's worth, remember the cloud base was in the vicinity of 1700 ft above *MSL* (I am using GPS altitude in these plots).
I've watched three videos of this, one from several miles upwind more or less in line with the runway (posted by skadi at #468). It looks like the disappearance in cloud is about double the height of the low point before climbing, but that's only an approximation. The video has the aircraft in cloud for about 34 seconds. Fitting that on your height plot, that would have the base slightly over 2000 feet (edit: amsl) Incidentally, also about that video, there isn't any apparent sideways movement, so I still haven't figured out why some people are talking about a bank angle. |
This is where a post-CPL course is aerobatics and gliding would be beneficial to all new candidates, to stretch their horizons and abilities. Experiencing an upset for the first time with pax on board is not the best time to discover you are uncomfortable with the sensation, or don't have an automatic stall identification and response reflex (Air France please note). In D.P.Davies' classic book written in the 1960s "Handling the Big Jets" the author suggests all line pilots should do 5 hours per year in basic a/c practising recovery from unusual attitudes/positions. I also agree with your comments about reaction to zero-g. |
The AND trim was either accidental(I agree highly unlikely) or an overcompensation for the pitch attitude associated with a GA with low weight aft cg and sustained gale-force headwinds.
The Dont do this is either from the PF if the trim input was accidental or from the PM if it was overcompensation from PF. The Jammed elevator sim scenario teaches pilots to respect the power of the THS.Anticipation and the dangers of overtrimming are quickly appreciated when doing this training.Short bursts of trim(esp when flaps down) is key.Concern with extreme ANU/AND attitude can sometimes lead a pilot to overcompensate. If a runaway (ac problem) then why the Dont do this? |
Will be interesting to see if the windshear alert sounded and/or stick shaker activated at any time.
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There are parallels being drawn with TA363 and there are some similarities but at the same time, some significant differences.
TA363 was about 80-90kts slower so a push-over was necessary to avoid a stall. The FlyDubai trace shows a segment of high pitch (consistent with encountering a positive shear and trying to keep constant IAS, whether manual or automatic) but a recovery to normal attitudes and IAS afterwards. The aeroplane then followed an unremarkable flightpath for 10-15s until pitching down rapidly towards the ground, accompanied by expressions of incredulity from the pilots. There is very little that supports any kind of stall. If the stabiliser had stalled with a positive AoA, the end result would have been less of a pitch down moment, although the blanking effects on the elevator are uncertain. There probably was icing around but why should the aircraft suffer serious adverse effects from it when accelerating to the highest IAS for some time? You’d have expected it to happen at slow speed and high AoA, neither of which were present when the LoC appears to have happened. At the moment it’s pointing much more towards some kind of flight control failure; whether or not it was recoverable we’ll have to wait and see. |
There are some significant human performance issues raised in the TA363 report . From Aviation Herald:
The MAK reported that the French BEA performed a sensorical simulation with the aim to model how the crew could lose spatial orientation. The model suggested that after initiating the go around the feel of the pitch angle of the crew and the actual pitch angle were in agreement until about +14 degrees, when the nose rose further to 25 degrees the crew still felt the pitch increase to 17 degrees. Subsequently, when the actual pitch began to decrease the felt pitch continued to increase until reaching +25 degrees, in this phase first nose down inputs are recorded on the flight controls. The felt pitch and actual pitch subsequently completely separated, as the aircraft settled in the dive further increasing nose down inputs were recorded. The MAK reported that the British AAIB performed simulations with the aim to determine whether somatogravic illusions were present. The AAIB concluded that in the absence of proper control of the instrument readings the crew could have perceived during the transition from climb to dive after the missed approach, that the aircraft was flying inverted. The MAK performed simulator tests with a number of pilots having them go through a scenario similiar to the accident flight, in particular forcing a go around at intermediate height with the autopilot disconnecting at the initiation of the go-around by pressing the TOGA button. The MAK reported that the vast majority of crews coped well with the scenario but found it difficult to master reporting highly increased stress levels, especially when the pilot monitoring did not provide full assistance. A number of pilots, although the autopilot disconnect aural and visual alerts are very distinct and have high attraction potential, did not catch the fact, that the autopilot had disconnected, several silencing the alerts by pressing the AP disconnect button, a number (about 42% of the pilots tested) not recognizing the alert at all and therefore responding with a substantial delay or not reacting at all. None of the pilots participating in the test was able to answer all questions to the procedures correctly, the MAK reported that 28% even believed the go around was automatic on autopilot despite the AP disconnect alert indicating lack of knowledge and a substantial gap between theoretic knowledge and practical skills. Of all pilots participating in the test only one third mastered the go around successfully. Only 28% attempted to achieve a suitable pitch angle after initiating the go around aiming for +15 degrees of nose up, others began to react only between +20 and +37 degrees of nose up attitude and airspeeds as low as 90 KIAS with stick shaker activation. None of the pilots was able to level off at the assigned altitude. In a second part of the experiment a test pilot produced a pitch up upset similiar to the accident flight and then let the participating pilot recover the aircraft. None of the pilots took the right decisions and none was able to recover the aircraft. The most common mistake was to believe, the control wheel would return to the neutral position on its own, this mistake however resulted in a substantial acceleration of the nose down movement resulting in rapid increase of the dive and vertical accelerations between +0.5G and -1.2G. The MAK annotated that in real flight such an acceleration likely causes the temporary and permanent incapacitation of passengers, cabin crew and even flight crew and may cause injuries to occupants. The common mistakes during the upset recovery noted by the MAK were non-optimal application of flight controls especially if the aircraft is in a bank, no reselection of flaps in order to adjust to the current airspeed resulting in flap limit exceedance and loss of additional height, the non-use of speed brakes. The MAK reported, that after demonstration of the correct upset recovery technics almost all pilots were able to apply the technics and recover the aircraft, suggesting that the result of the experiment was mainly the result of lack of pilot training with respect to upset recovery. |
Total speculation here, and nothing I can point to in support of this, but I'm willing to make a bet that wind shear wasn't a factor.
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I noticed nothing said about recovering from a extreme nose high attitude and low airspeed by rapidly unloading and rolling the aircraft with full aileron/spoilers into a 45-60 degree angle of bank to get the nose to drop. That is the advice in the 737 FCTM.
Also, to clear the decks as it were, the flight director should be immediately switched off if encountering a gross unusual attitude. This action is to avoid unwanted distraction of FD needles blocking the view of the basic raw data as displayed by the ADI. FD use and subsequent addiction as espoused by many operators can be potentially deadly in extreme UA recoveries |
Extreme nose-down attitude
Since 2000, several incidents have involved extreme nose-down attitudes during the go-around maneuver on different types of airplanes from different manufacturers. These incidents often result from a breakdown in correct cockpit instrument scanning. Here are some examples:
After the PF initiated a manual go-around at night over the sea, at 1,000 feet (305 meters), the PF kept a prolonged pitch-down input resulting in a 15-degree nose-down attitude and a dive that was not recovered before the impact with the sea. The amplitude and duration of the initial reaction by the PF to the “pull-up” warning from the ground proximity warning system (GPWS) was insuficient (i.e., a full back stick input was required). After the PF initiated a manual go-around in instrument conditions, and approaching 2,500 feet (762 meters), the ight director altitude capture mode was activated earlier than expected by the crew because of a high rate of climb. The PF manually initiated a level-off but kept a prolonged pitch-down input that resulted in a dive that reached an extreme negative attitude (minus 40 degrees). The PF recovered from the dive at about 400 feet (122 meters) above the ground with a vertical acceleration of 3.6 g-force (g). |
Video of a runway stabiliser in a 737CL simulator.
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Instead of all the speculations and redesigning the B737. does anyone have any information from the voice or data recorders?
You remind me with the last crash of Air Asia, were a program was made about it assuming that the weather was the cause of the crash, and at the end, the reason was the captain pulling circuit breakers during cruise. |
Copy/paste from Boeing?
@GNS APPROACH
Extreme nose-down attitude Boeing drivers would no doubt be aware, but for the rest of us, including interested lurkers like me, don’t you think you should have acknowledged the source and context of the 3 paragraphs of your post, that you lifted verbatim from the following Boeing article: "Performing Safe Go-Around Maneuvers”, Aero Magazine, Issue 55, 3rd Quarter 2014. Available online at http://www.boeing.com/commercial/aer...ERO_2014q3.pdf Further on in that article is this rather alarming statement (which may or not be relevant to this crash): “When pilots are distracted, an airplane could change its flight path from a normal go-around climb to a steep dive in fewer than 10 seconds.” |
Did the aircraft have the Speed Trim System?
Haven't seen any discussion about that, but I would think it would apply.
Originally Posted by SmartCockpit B737NG
Speed Trim System
The speed trim system (STS) is a speed stability augmentation system designed to improve flight characteristics during operations with a low gross weight, aft center of gravity and high thrust when the autopilot is not engaged. The purpose of the STS is to return the airplane to a trimmed speed by commanding the stabilizer in a direction opposite the speed change. The STS monitors inputs of stabilizer position, thrust lever position, airspeed and vertical speed and then trims the stabilizer using the autopilot stabilizer trim. As the airplane speed increases or decreases from the trimmed speed, the stabilizer is commanded in the direction to return the airplane to the trimmed speed. This increases control column forces to force the airplane to return to the trimmed speed. As the airplane returns to the trimmed speed, the STS commanded stabilizer movement is removed. STS operates most frequently during takeoffs, climb and go-arounds. Conditions for speed trim operation are listed below: • Airspeed between 100 KIAS and • Autopilot not engaged Mach 0.5 • Sensing of trim requirement • 10 seconds after takeoff • 5 seconds following release of trim switches |
Yes it does.
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Originally Posted by tarik123
(Post 9324927)
Instead of all the speculations and redesigning the B737. does anyone have any information from the voice or Data recorder?
The Air Accident Investigation Commission jointly with the experts from the participated States continue work on addressing the possible scenarios of Boeing 737-800 A6-FDN (FlyDubai) aircraft accident. The meteorological conditions near Rostov aerodrome are being analyzed, as well as aerodrome aids, ATC and AirMet service actions. ATC data from other aircrafts that conducted their flight in the same area are used during this analysis. In the IAC Laboratory, the work on the flight recorders' and ground aids' data is continued. With the use of onboard recorders' data and all necessary flight and engineering documentation the aircraft systems' operationability is being analyzed, including the aircraft and engines control systems. The flight crew state during the accident flight is also being analyzed. The identification of recovered aircraft fragments and the layout is in progress. As always, it'd be wise to stick with official sources. |
“Except perhaps when ALTERNATE LAW comes into play?”
Of course. It goes without saying. But the bus is in normal law 99.9999% of the time and has saved MANY people from screw ups that a 737 cant save you from. “Yes, because the best solution for pilots loosing basic stick and rudder skills is to just put a computer to do that for them…..” What is a better solution? Removing technology that provides protection? “... And we know how that turned out with AF447...” Yes, a poorly trained crew will always find ways to crash a plane though. I find it truely alarming that so many pilots on this website have such vastly differing opinions about how FD's work and stab trims and windshear recoveries. Shouldnt we ALL be precisely on the same page with these basics? |
Oh, there has been some super analysis and some speculation on the 47 odd pages.
Should we not await the DFDR & CVR details, surely that is the truth... |
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