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SHK has shared some FDR and CVR data in this statement.... SHK webaite: http://www.havkom.se/en/
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Well from that admittedly limited information it sounds like some dramatic structural failure.. Total duration of the event was about 90 seconds. Final report is due in December. Lets hope that a lot of the details get filled in before then. |
Machinebird
I read both the Swedish and English statements and nowhere did I find any reference to autopilot being re-engaged unless there are some subtleties about Mach trim that is linked only to autopilot re-engagement. |
I watched the webcast from the presentation of the report. HAVKOM pointed out that four FDR channels (pitch, roll, ground speed and mag heading) were incompatible with other data after the event started. All these channels are generated by the IRU.
So they made a graph showing both the FDR pitch data and their "best effort estimate" of the actual pitch. The graph shows that the FDR pitch suddenly indicated up. After 2-3 secs the estimate indicates a pitch down which increases, with -1g negative pitch acceleration. To me, this would fit a scenario where the PF sees a pitch up on the PFD and reacts by pushing down and trimming nose down (as also recorded on other FDR channels). Overspeeding occurs after approx 15 seconds. Note that the investigators did not confirm such a scenario, but did not deny it either. |
Extracted from the preliminary accident report:
http://www.havkom.se/assets/reports/SRL-2016_01e.pdf After one hour and ten minutes of flight, during the pilots approach briefing, the pilot in command, who was seated in the left seat, exclaimed a strong expression. Immediately thereafter the aural warning for autopilot disconnect (named Cavalry Charge) was activated. The disconnection was also confirmed by FDR data. The warning sounded continuously during the following 18 seconds. After the autopilot disengagement FDR data indicates that both left and right elevators moved towards aircraft nose down position. Left and right side angle of attack went towards negative values. The aircraft entered a descent with vertical acceleration values that reached a negative load corresponding to -1G. After a few seconds of negative G-load the aircraft's warning system was activated by a so-called Triple Chime 10 followed by an aural warning (synthetic voice) for low engine oil pressure on both engines. FDR data shows that the trim to the movable horizontal stabilizer was activated manually and the trim position went from -0.9 degrees nose up to 1.7 degrees nose down. An aural signal of the stabilizer trim movement (Stab trim clacker), signifying a manual input longer than three seconds, was activated in connection with this. Immediately thereafter a warning for high bank angle was activated. After 17 seconds from the start of the event, the maximum speed (VMO), 315 knots was exceeded. The over speed warning was activated and the vertical acceleration turned to positive values. Another 16 seconds later, the first officer transmitted a “MAYDAY” message that was confirmed by the air traffic control. The indicated airspeed then exceeded 400 knots and the stabilizer trim was reactivated and dropped to 0.3 degrees nose down. The Pilot in Command called "Mach trim" 11 after which engine power was reduced to idle. During the further event the last valid FDR value shows that the speed continued to increase up to 508 knots while the vertical acceleration values were positive, with maximum values of approximately +3G. FDR data shows that the aircraft's ailerons and spoilerons mainly were deflected to the left during the event. Radar data and the accident site position indicate that the track was changed about 75 degrees to the right during the event. The crew was active during the entire event. The dialogue between the pilots consisted mainly of different perceptions regarding turn directions. They also expressed the need to climb. The aircraft collided with the ground one minute and twenty seconds after the initial height loss. The interview in Dubai had this comment in it: (please make allowance for google translate) I do not see any such reference in the preliminary report. Eleonor Norgren: There are no ready answers. But the crew regarade that something was not as it should, and coupled the autopilot. The process must have been under a minute and a half. |
Machinebird
It is to me very very clear that google translate was not correctly tuned for this translation. Your quote: Eleonor Norgren: There are no ready answers. But the crew regarade that something was not as it should, and coupled the autopilot. The process must have been under a minute and a half. Eleonor Norgren: Det finns inga färdiga svar. Men besättningen regarade på att något inte var som det skulle och kopplade ut autopiloten. Förloppet ska ha varit under en och en halv minut.13:21, 9 March 2016 ?Besättningen reagerade och kopplade ur autopiloten? - P4 Norrbotten | Sveriges Radio My translation would absolutely be There are no ready answers. The crew reacted on something that was not as it should and disconnected the autopilot. The process (/event/incident) should have taken less than a minute and a half. Clearly a mistake from automatic translation. |
MrSnuggles,
Thank you for the clarification. That makes better sense. Looks like the guy flying was trying too hard to chase an illogical PFD display. If the plane has been flying in stable flight with the trim set, why would you be running in a bunch of trim manually once control has been dumped in your lap? Zero g in cruise? That can't be good ! Sit back and size up the situation before you set out on your course of action. At least that is what I was taught.:hmm: |
Picked this comment out of the report:
FDR data shows that the aircraft's ailerons and spoilerons mainly were deflected to the left during the event. |
Not trying to defend or praise the crew as the report is still quite sparse. However, as pilots it's drummed into us to always trust your instruments and not your senses.
Machinbird, as you say going from perfectly trimmed to an illogical scenario in a few seconds should have alerted them to the fact that maybe the instruments were giving dodgy readouts. Surely a quick glance at the standby instruments would've confirmed they were straight and level to start with? If this had happened in the day or with visible references outside I suspect the outcome would've been far more positive. All the holes lined up on this occasion... Champ |
The process must have been under a minute and a half. |
Actually the first deviation from normal on the FRD data released was the pitch showing constant nose up with a rate of about 30 degrees in 4 seconds, until almost 90 degree nose up after 22s.
Second sign, A/P disconnect about one second after pitch moving upwards. Until AP disconnet all other values vas normal, 1G and no pitch or roll commands or movements. Does not look like structural failure. There is a clear connection between elevator position, AoA and G all the way down. And its quite clear that the pitch values(from IRSIRU) is corrupt. |
Essential information (CVR & FDR) from the preliminary report for everyone's convenience:
CVR (Throughout the transcript, different alarms, chimes, and warnings are continuously heard) 23:19:22 (CPT): [expletive] 23:19:29 (FO): [expletive] 23:19:30 (CPT): [expletive] 23:19:33 (FO): Come on 23:19:35 (CPT): Come on, help me, help me, help me 23:19:35 (FO): Turn right 23:19:36 (FO): What 23:19:37 (CPT): Help me, help me 23:19:38 (FO): Yes, I'm trying 23:19:40 (FO): Turn left, turn left 23:19:43 (FO): Turn left 23:19:44 (FO): No 23:19:50 - 23:20:09: FO transmits the standard mayday call and repeats it several times 23:19:59 (CPT): Mach trim 23:20:01 (FO): Trim, trim a lot 23:20:06 (FO): Turn left, turn left 23:20:14 (CPT): We need to climb, we need to climb 23:20:15 (FO): Yeah, we need to climb 23:20:16 (FO): Turn left, turn left 23:20:17 (CPT): No, continue right, continue 23:20:19 (CPT): Continue right 23:20:20 (FO): Ok 23:20:22 (CPT): No, help me, help me please 23:20:23 (FO): I don't know, I don't see anything 23:20:24 (FO): I think you are the right to correct [sic] 23:20:25 (CPT): Ok 23:20:26 (CPT): Ok, ok, ya 23:20:28 (CPT): [expletive] 23:20:31 (FO): [expletive] FDR (Apparently the recorded pitch angle is not compatible with the aircraft's motion. Recalculation of pitch angle is shown beneath the FDR) https://i.imgur.com/ScI7umC.png Recalculated (more likely) pitch angle information from TAS, altitude, and AoA: https://i.imgur.com/8WukfMI.png |
Immediately thereafter the aural warning for autopilot disconnect (named Cavalry Charge) was activated. The disconnection was also confirmed by FDR data. The warning sounded continuously during the following 18 seconds. When either pilot disconnects the autopilot the calvary charge aural will only alert once for about 2-3 seconds. When the autopilot disconnects automatically because of a failure it will continue to sound the calvary charge aural until a pilot manually selects the autopilot disconnect switch and that will silence the aural. It sounds to me like the autopilot disconnected automatically. |
Runaway trim or a hyd hardover in pitch leading to UA?
:ooh: |
From my reading of the report I'd still think that a major failure was the cause of the accident. Sure, the crew were trying to control the aicraft to the bitter end; but so were the Alaska Airlines guys when their stab broke loose. They had zero chance. With any element of control, I'd expect a couple of partial recoveries, yet they went straight down.
I think that the investigators have some idea of what they are looking for. When the weather improves, I think that they will return to the accident site to confirm what they suspect. |
Three bad FDR parameters
Wrist watch: Actually, three parameters were listed as not compatible (on p.23 of the report): färdhastighet (ground speed), tippvinkel (pitch angle), and rollvinkel (roll angle).
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if they suspect htp runway then it needs to come out a.s.a.p., but also, what could have caused it.
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As we can see on the posted FDR-data, pitch information was leading(but most certain, not true).
Elevator pos, trim pos, AoA and G was not affected until after A/P disconnect. Does'nt look like any other failure but IRU/IRS. |
Possible chain of events
So...to elaborate on AAKEE:s earlier summary:
1) A/P disconnect (due to incorrect pitch indication from IRU?). 2) PF pushes nose down 1s later (due to incorrect pitch indication on PFD?). 3) g loading and AOA follows. 4) PF pushes nose down multiple times in coming seconds. 5) Stab trim increases towards nose down pitch. 6) Alt decreases, speed increases until overspeed. 7) At overspeed warning PF pulls nose up (realizes instrument error?) but does not recover (aeroelasticity?). 8) RIP. |
If you look at the blue line of indicatet pitch it seems like when captain is diving with an estimated 30 to 40 degrees down the iru in fact is telling him that this is working because its comming down. Then the estimated pitch is reduced. Then it is going way up again and he is diving again to repeat what he is thinking is the correct recovery. Scary!
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What would make the IRU fail so suddenly the autopilot would automatically disconnect (as per cappt's experience)? What would cause pitch angle to be extremely misleading?
Bad sensors? Icing on sensors? Sensors falling off in flight? Broken gyros? Is this a maintenance issue? Right now the aircraft is pretty much frozen solid into the ice and snow in northern Sweden. Any investigation regarding instruments left up there would have to wait until spring.. that would be May at the earliest that far up north. |
There should have been an EICAS and PFD warning message, when the two units driving PFD1+2 disagree. I am not suggesting AHRS/IRU failure here, just one thing of several that will disconnect the autopilot. Will the FDR record info from both PFD's and the standby info or only the captains/flying pilot? |
I would think that normal procedure would be for CPT to fly AHRS1 to his PFD and FO would fly AHRS2 to his PFD, however looking at the text of the discussion between the two crew members, the FO doesn't seem to be aware of the problem with the CPT display. Does anyone else get the feeling that they were both on the same (failed) AHRS? Other than a previous failure of one AHRS, why would both crewmembers be using the same AHRS? Switchology?
Will the FDR record info from both PFD's and the standby info or only the captains/flying pilot? |
Will the FDR record info from both PFD's and the standby info or only the captains/flying pilot? I wonder which IRU feeds the standby attitude indicator? Or is it a separate gyro? I also wonder about similar accidents where in spite of warning chimes and flags on the PFD, the pilot has just chased the invalid attitude indicator? Something for human factors people and instrument designers to rethink? |
bank angle at event:
initially: left aileron, followed by left bank; then: right aileron until bank 0; followed by: continuous, hard left aileron and a complete roll over to the left At a first, superficial view I can't see a discrepancy between the roll inputs and the roll rate. Seem to corelate. I only know the PFDs in GA airplanes, but at very high or low pitch angles, there are mainly chevrons and air or ground to see, leading attention to pitch instead of bank and making it a bit more difficult to control bank. The conversation makes me think that there is a good chance that both PFDs were on IRU1, as Machinbird supposed. No call from the FO for need to pitch up. Would normally be the main objective in that situation, approaching VMO. The stand-by PFD or AI should have a separate IRU. |
If you assume that the pilot was reacting to the displayed bank, then his inputs will appear to correlate with the bank angle, naturally. That doesnt, in itself, validate the bank angle. Indeed, if you look at about 23:19:50, thee are 5 to 10 seconds of sustained left wing down aileron (more than 10 deg) at a VERY high airspeed. This should roll the aircraft rapidly left wing down. It doesnt, it stays right wing down, according to the bank angle. So while the aileron correlates witn a pilot trying to correct the bank, the bank doesnt respond to the aileron. Suggesting bank is, as stated by SHK, unreliable.
Oh and at these speeds, the aircraft WILL respond to roll inputs, quickly. The aircraft, at least at this point, is still inside the certified envelope and is not subject to aeroelastic loss of control, as some have suggested might be occurring. By regulation, you have a minimum 15% margin above VD/MD, which in turn has a good margin to VMO/MMO. You have to be going incredibly fast to see the aeroelastic effects become significant. The elevator also correlates with the displayed pitch - pushing whe pitched up or pitching up, pulling whe pitching down or pitched down - and no one is suggesting that validates pitch. The standby is indeed truly independent. There were, at least in theory, three independent attitude sources available. |
@ Mad FS:
The provided diagrams are labeled: pitch > 0 means climb, and elevator > 0 commands up whereas bank > 0 means RT and aileron > 0 commands LT; reversed reading for the bank part in the graphs. Thus, the pitch commands seems to be reaction in opposite direction of the indicated, after a couple of seconds of drifting upwards. The roll commands are in the same direction of the deflection: aileron left, with roll rate to the left; then right, with rate to the right, then left with rate to the left. At 23:19:50 the aircraft is already in a 150 ° left turn. Until then, it seems corelating. I don't know if bank information in reversed flight is reliable nor how a CRJ behaves at such an attitude. |
Andi, as the SHK did state that bank angle is unreliable I wouldn't put too much interpretation into it.
What does strike me (again) is how important it is to have the CVR data as well as the FDR. Without the CVR we might spend hours (well, MORE hours... ;)) trying to decode what the pilots were trying to do. With the CVR at least we have a clue that - as QDM pointed out - their focus was initially on the bank, not the pitch. /N |
As pointed out, there are three sources of attitude information, the left and right displays, plus the standby, when two out of three should agree, with the standby often referred to as the "tie-breaker," since it's assumed that it should agree with the left or the right display, whichever one is correct.
From what we've been told, it reads as if the PF took the aircraft and tied it into a knot chasing an unreliable attitude display. From that point it was probably very difficult to figure out just what the airplane really was doing since it would have been at some extremes of pitch and bank, plus at negative G at times, and all on a dark night with little or no outside references available. Then to look at three displays and to pick the two that were correct would have been pretty difficult. Is that 90 seconds from start to impact? That would imply a vertical speed of about 20 thousand feet per minute, or 300 knots. |
Is that 90 seconds from start to impact? That would imply a vertical speed of about 20 thousand feet per minute, or 300 knots. I have only flown steam gauges, but it even there it can be an issue understanding the displays as you approach vertical flight. From what I've seen in mockups, modern PFDs are optimized for ~horizontal velocity vectors and may be completely inadequate for useful guidance in vertical flight. Has anyone here ever done a loop in the CRJ simulator to see what the display does? |
During extreme attitudes (-20/+30 or 65 deg bank) the PFD will de-clutter and red chevrons appear pointing to the direction of level flight.
I think this mostly industry standard now on EFIS equipped aircraft. |
@AK
@ Mad FS: The provided diagrams are labeled: pitch > 0 means climb, and elevator > 0 commands up whereas bank > 0 means RT and aileron > 0 commands LT; reversed reading for the bank part in the graphs. Thus, the pitch commands seems to be reaction in opposite direction of the indicated, after a couple of seconds of drifting upwards. The roll commands are in the same direction of the deflection: aileron left, with roll rate to the left; then right, with rate to the right, then left with rate to the left. From 23:19:38 (approx) to 23:19:54, the ailerons are consistently positive. That means they are commanding left-wing-down roll (as noted on the plot and mentioned in your post). During that whole time the bank angle is positive - RIGHT wing down (again, as you note for the sign convention) - and INCREASES, which means rolling further to the right. So the ailerons should be creating a left roll, but the bank trace rolls RIGHT. The roll commands are NOT in agreement with the bank response - they are in the sense to oppose the bank angle - suggesting crew action in response to the displayed bank, but that the crew action was not reflected in the bank angle recorded. @Niclas - don't totally dismiss the bank. What SHK has said is that it doesn't seem to be compatible with the aircraft motion. they haven't said its "invalid" and it's probably a good assumption that the FDR was correctly recording the bank angle it was receiving, and that same bank angle (and pitch also) were being displayed to at least one set of cockpit displays. So it may be fundamental in determining why the accident happened. We just have to be careful in relating "indicated" attitudes to the likely "true" attitudes. |
Could it be that they encountered roll reversal due to being supersonic or transsonic? This will explain why the aircraft rolls opposite the command roll.
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Originally Posted by F-16GUY
(Post 9307095)
Could it be that they encountered roll reversal due to being supersonic or transsonic? This will explain why the aircraft rolls opposite the command roll.
A quick calc of IAS Vs altitude tells(wihout temperature corrections made) Mach topped about 0.95 around FL260. It was quite cold so I guess it came closer to transonic at lower alt, despite a FL-to-CAS-calc dont say so. |
7-cylinder man
At least I'm pro enough not to call others for amateurs. So now please enlighten all us amateurs. By the sound of it you got it all figured out. My question referred to the timeframe between 23:19:38 and 23:19:54 where apparently the aircraft was rolling in the opposite direction of what was commanded. I do agree that loss of one PFD should not lead to the loss of the aircraft and its crew, but I wasn't there and I bet there is a lot of factors that the Swedish Board of Investigation will look into. I would say that the only one jumping to conclusions right now is you... |
7-cylinder man
Honestly, do you amateurs know nothing? Read and think why the FDR was recording what it was. It's all there. An IRS/AHARS failure shouldn't lead to the loss of an aircraft - it's not even classes as an emergency procedure in any type I've flow; abnormal procedure yes. From what has been published of the CVR recording the failure was never addressed or diagnosed by the crew. The PF seems to have jumped to a conclusion rather than diagnose the situation. Put simple, the failure was not diagnosed by the crew and there was a rush to an incorrect conclusion. I can agree that loss of one instrument or reading should not lead to loss of an aircraft. Still, that happens. Most of the times during night with no visual references. Just as in this case. That is sad. On another note, I still wonder what might have broken with such short notice as hinted at on the CVR. The crew offers a few expletives and then the plane crashes within 90 seconds. Things went downhill even faster than any Airbus during malfunctioning FOs. As Mr 7-cylinder man says, there are no clear indication on the CVR what went wrong. Some hints by the FO that they disagree on what direction to bank... maybe, depending on how you read it. Whatever happened it did so very sudden (as I read the CVR) and the crew was more occupied with trying to fly the plane than communicating with anyone. Is it possible that this lack of communication between the pilots indicates that they had the same (wrong) mental picture of the situation? May they both have been fed the wrong information somehow? |
I truly hope that there is a conclusion drawn from this accident when the final report is published. On first sight it looks very complex. It appears that we are into a what / who failed first endgame.
I have two cars, one is state of the .. and if something quits .. you pay BMW for a new box. The other is 1968 and of UK origin. If something quits you proabably knew about the possibility of failure, and the appropriate action anyway. Times have changed. |
The nasty part about an attitude system failure is the crew can follow erroneous indications until it becomes apparent that the aircraft is in a very bad place.
By this point the other attitude sources will also be showing unusual attitudes and the crew will likely be in a situation they have never seen or trained before. Lack of air data makes it difficult to demonstrate such a failure in a sim with good fidelity. Should we do certain upset training in military trainers? Were there alerts for attitude systems disagree? If so, they seem not to have gotten the crew's attention in time:( |
Were there alerts for attitude systems disagree? If so, they seem not to have gotten the crew's attention in time |
How about equipping crews with night vision goggles, or pilots carrying their own? They aren't that expensive, and being able to see a visible horizon at night once the SHTF might be a life saver.
I don't mean they should be worn routinely at night, just available for quick donning. |
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