Candair CRJ200 from Heathrow Declares then Disappears

gotWXdagain said:
Recently I had an electric trim switch short out such that applying nose up trimmed the airplane nose down, and applying nose down trim did nothing.
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The thing is, a full 2 secs elapses (each tick mark is 2 secs) before the stab trim moves AFTER the PIC states surprise at the change in pitch. Stab trim runaway just doesn't fit the data in my opinion.

image.jpeg
 
GypsyPilot said:
As others have said, it's manual electric. I have several thousand hours in the CRJ, and this is just a strange report so far. As I said previously, the main problem with your theory is that a trim runaway doesn't match the timeline. Crap hit the fan before the stab trim moved.
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Interesting, after re-reading I get what you're saying.
 
Roger Roger said:
Was it manual, or manual electric trim? If manual then yes, not a trim runaway but if it was manual electric trim then it still seems possible, I can't think of any other good reason to trim 1.9* nose down a cruise speed.
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If memory serves, that seems pretty close to our trim in cruise.
 
In this image you can see what the FDR recorded vs what the investigators calculated actually happened. The FDR recorded a pitch of 80º nose up but the plane was actually 40º nose down.

CZ8eKzI.png


This makes it look like there was some AHRS failure that caused the captain's PFD to indicate 80º nose up. He then pushed full nose down and trimmed trying to fix it. The autopilot disengaged on its own, possibly because of the AHRS.

In the first graph, is the pitch showing positive or negative? Because that first graph makes it look like the plane also started to pitch down on its own before the autopilot disconnect.
 
thevideographer said:
In this image you can see what the FDR recorded vs what the investigators calculated actually happened. The FDR recorded a pitch of 80º nose up but the plane was actually 40º nose down.

CZ8eKzI.png


This makes it look like there was some AHRS failure that caused the captain's PFD to indicate 80º nose up. He then pushed full nose down and trimmed trying to fix it. The autopilot disengaged on its own, possibly because of the AHRS.

In the first graph, is the pitch showing positive or negative? Because that first graph makes it look like the plane also started to pitch down on its own before the autopilot disconnect.
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The FDR data shows all kinds of weirdness, with a pitch up accompanied by an increase in true airspeed, a decrease in altitude, and a DECREASE in ground speed.
 
GypsyPilot said:
The FDR data shows all kinds of weirdness, with a pitch up accompanied by an increase in true airspeed, a decrease in altitude, and a DECREASE in ground speed.
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How is that possible? I could see the AHRS failing giving false attitude info but with correct air data. Wouldn't the groundspeed GPS based and separate from the AHRS?
 
I suppose but I guess I need to look at the data more carefully. For the majority of that time pitch wasn't that steep and TAS was very high - I wouldn't expect groundspeed to go down until the end when it was nearly vertical.
 
thevideographer said:
I suppose but I guess I need to look at the data more carefully. For the majority of that time pitch wasn't that steep and TAS was very high - I wouldn't expect groundspeed to go down until the end when it was nearly vertical.
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40 degrees nose down is a lot.

Sent from my XT1254 using Tapatalk
 
This is insane. I can't even begin to imagine what these guys had to deal with the last 1:20 of the lives. Fair winds and fluffy clouds!

My monday morning quarterbacking is going with an old school attitude failure. Maybe not the whole AHRS, but just the pitch laser. If the system "recentered" itself slightly off kilter, or if you got a slight bit of moisture in there, a centered laser could be mistaken for a steady climb. Look how linear the pitch changes are and how sinusoidal the graph is. That bodes for it being off kilter, but still "working". What would you do if your PFD suddenly showed you in a steadily increasing climb? You'd shove the nose forward. In theory, the CRJ PFD would go black and show a big red X, but who knows, maybe there's some programming failure mode that doesn't do that?

I also notice that the power wasn't really touched until the displayed pitch came back down through level, at which point it went to idle. That seems relatively instinctual, and also tells me that the PFDs didn't go black.. And the roll? Holy hell. I can only imagine the confusion on a flight deck when the attitude indicator shows you pointed to the sky, the overspeed clacker is going off, and your engines are screaming at you for oil.
 
Xcaliber said:
This is insane. I can't even begin to imagine what these guys had to deal with the last 1:20 of the lives. Fair winds and fluffy clouds!

My monday morning quarterbacking is going with an old school attitude failure. Maybe not the whole AHRS, but just the pitch laser. If the system "recentered" itself slightly off kilter, or if you got a slight bit of moisture in there, a centered laser could be mistaken for a steady climb. Look how linear the pitch changes are and how sinusoidal the graph is. That bodes for it being off kilter, but still "working". What would you do if your PFD suddenly showed you in a steadily increasing climb? You'd shove the nose forward. In theory, the CRJ PFD would go black and show a big red X, but who knows, maybe there's some programming failure mode that doesn't do that?

I also notice that the power wasn't really touched until the displayed pitch came back down through level, at which point it went to idle. That seems relatively instinctual, and also tells me that the PFDs didn't go black.. And the roll? Holy hell. I can only imagine the confusion on a flight deck when the attitude indicator shows you pointed to the sky, the overspeed clacker is going off, and your engines are screaming at you for oil.
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If a failure like what you're suggesting occurred, an "ATT" flag and accompanying caution would be produced, alerting the crew to the issue. The QRH would rather quickly help them diagnose such AHRS was the issue.
 
I'm not intimately familiar with the CF-34 engine design but could the oil alerts be due to negative G's that came with the nose over?
 
Table Two said:
Scary stuff.
Both heads down during approach briefing.
Then CA had PFD show 15 degrees nose up while in level, unaccelerated flight. FO PFD showed level flight. CA made an upset aircraft recovery based on faulty indications.
Aircraft hit the ground at 508 KIAS.

http://avherald.com/h?article=4920a18a/0000&opt=0
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Having experienced an AHRS failure in that airframe, in IMC, that was a tough read. Regrettably the "confirm" part of recognize, confirm, recover doesn't seem to be taught outside of military and primary training.
 
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