There is no manual trim wheel on this type either.

It's happened to me that both pitch trim channels failed at cruise speed and we were left with an uncomfortably out-of-trim airplane as we slowed for approach.

I can only imagine if a HS runaway were not disconnected early via disconnect switches or CB, what the elevator forces would be with no manual trim reversion to correct the problem.

I'm surprised that the aircraft would be certified without some means to recover to a good trim setting. If all you have is "Jack be nimble, Jack be quick, as a defense before it gets away from you, then that isn't too good. If you are flying on autopilot and the first you know of a problem is that the autopilot has been overpowered, and the aircraft is pitching down, then you are already too late. Even the relatively simple Douglas designed, THS equipped, A-4 Skyhawk had a pitch trim "crowbar" lever that let you manually overpower whatever signals were trying to move the pitch trim actuator screwjack.

Limited information I've seen on the CRJ indicates that there is probably a pitch trim force warning light before the actual A/P disconnect. Is that correct?

Phoenix`s question is worthy of further consideration.

Flight was airborne at 23:10 and crashed at 00:18. I estimate distance to destination was approx 1000 miles, possibly duration of some 2hrs or so.
The crash site near Akkajaure Lake and Tipel (FIR Bdry) would be some 400 miles to run to destination.
I would have thought it early for TOD.

Am not familiar with route. Anyone familiar with the route may perhaps enlighten us further.

604 nm according to Great Circle Mapper

I have experienced it in the sim. It is violent and uncontrollable unless immediate action is taken. At low altitude it is fatal. The change in attitude is so sudden that if you don't have your wits about you, you forget to push the master disconnect and just pull on the yoke for dear life. I suspect that they may have had a runaway, were taken completely by surprise and didn't know what hit them. If I remember correctly, Stab Trim Runaway did not even have memory items until late 2000's. Can any old CRJ guys remember when this was changed in the QRH?

The initial report leads one to believe that they were still at cruise altitude. No report of a request or clearance to descend. Descending normally from FL330 would only require about 120 NM (including decel). Additionally there is high terrain south of Tromso that keeps you at or above 5000ft until inside about 11 miles if landing Rwy 01 (~80% or more), so no, I don't think they were descending.

The CRJ trim system, by design, should detect un-commanded motion and shutdown. The problem referred to by some earlier posts is that there was a manufacturing defect at a supplier, and the circuit boards for the horizontal stab trim control unit (HSTCU) did not have the required conformal coating applied to the boards during manufacturing, which left the traces on the circuit boards exposed to the atmosphere. The result was that after many years in service, the traces on the boards could corrode, and the corrosion could bridge adjacent traces, creating circuits that weren't supposed to be there. This resulted effectively in a circuit diagram that differed from the design, creating paths for electricity to flow where it shouldn't, resulting in uncommanded trim motion.

It is well and good to have a perfect design, but you need to ensure the delivered product actually conforms to the design, or all the bright work of the designers is for naught.

This issue was covered by Transport Canada AD CF-2006-20. This AD, among other things, required the installation of new HSTCU, with conformal coating on the circuit boards. The accident aircraft should have had the new HSTCU installed many years ago, so accident should not be directly related to this old issue.

Thanks khorton,
The AD indicates that there are disconnect switches on each control wheel and I have seen pictures indicating a red 'pitch disconnect' switch on the left side of the center console.

When the autopilot is engaged, it has authority to command pitch trim motion, doesn't it? This type trim in a mechanical control system is usually activated by force sensing systems in the control linkage. Is that the case on the CRJ?
If so, then jams in the pitch control system can probably cause trim runaways.

Important caveat. I know next to nothing about the specific design characteristics of the CRJ. It is just that this specific situation has resulted in trim runaways in a number of different types of aircraft. Is there a common link? Design engineers are clever people and they learn from past problems and come up with novel solutions. They may well have circumvented this type problem with their HSTCU design.

... the crash site is about 125 NM out of Tromso
Great Circle Mapper

There are stabilizer trim disconnect buttons on each control wheel. The red "PITCH DISC" T handle on the left, front of the centre console is for jams in the control linkages in the pitch axis - it disconnects the linkage that connects the left and right control wheel in the pitch axis. If you pull that T handle, the left control wheel is connected only to the left elevator, and the right control wheel is connected only to the right elevator, allowing for continued control by one of the pilots after a jam in the pitch control system. A similar ROLL DISC handle on the right side of the centre console is used for jams in the roll axis control linkages.

The autopilot will command pitch trim to zero out any required elevator servo commands, after a short time delay (to prevent it from commanding trim in response to short duration elevator commands). The autopilot receives elevator position information, and I believe it would disconnect if the elevator position did not match the result expected from the amount of servo current, but I'm not completely certain of this.

khorton
Thank you again for your helpful descriptions.
This implies that there must be both right and left elevator servo valves and that the linkages between the control columns and the elevator servo valves are duplicated, probably all the way back from the cockpit. Since each elevator side is actuated by 3 cylinders on 3 different hydraulic systems, the servo valves are either a single valve body with 3 sections or actually 3 separate valves on each elevator side. Followup signals would probably be by means of a linkage attached to the individual elevators which is then summed with the associated input linkage. Autopilot trim inputs would then be taken directly off the summing linkage per your description. Then the question arises, are autopilot trim inputs taken from both sides and compared or from just one side? Or have I run well off the track?:}

Those design engineers are clever fellows and often do the unexpected to achieve their goals. I tried to download system information from Scribd, however didn't find much of great use.

There are three separate hydraulic actuators for each elevator. The servo valve controls have jam-tolerant mechanisms, so a jam in one servo valve control will not cause the whole system to be jammed. I'm not sure how the servo valves receive their position feedback from the elevators.

There are pitch control runs from each control wheel back to the elevator servos - left control wheel connected to left elevator servos, and right control wheel connected to right elevator servos. The two control wheels are connected via the disconnect mechanism (actuated by the PITCH DISC T-handle).

The autopilot commands to the HS trim have their source in the autopilot servo torque that is commanded. If the servo torque required exceeds some threshold for a minimum time, then the autopilot sends a command to move the HS.

Studying the maintenance manual a bit more deeply, it looks like my earlier statement that the autopilot receives elevator position feedback was probably incorrect. I don't see any such input on the spaghetti diagram for the autopilot.

[QUOTE=_Phoenix;9237934]... the crash site is about 125 NM out of Tromso
[url=http://www.gcmap.com/mapui?

TIPEL is 158.4 nm R-196 TRO. I would therefore agree with Phoenix that the likelihood of loss of control initiated with the descent from cruise level is probable.

It may be if the ATC transcript included a request for & clearance to . . descend. If not, well, I am guessing, as professional pilots, they didn't just start on down.

158 out is a bit early for a descent from F330.

mil radar data show that plane make a right turn to the east when desending.
LINK

Hi All,

Cl-604 incident (similar a/c systemwise).
https://www.gov.uk/aaib-reports/aar-...-november-2005

Cheers

Tamas

That incident was caused by corrosion on the horizontal stab trim control unit (HSTCU). There were several similar incidents, which triggered the AD mentioned earlier in this thread. That AD required replacement of the HSTCU with ones that had a conformal coating on the circuit board, to prevent such corrosion. Thus this accident should not have been caused by the same problem.

Is there any info on the loadplan?

A loadshift forward when starting descend due to no or broken forward uplocks will make a Freighter going in an unrecoverable vertical dive.

The laodshift theory doesn't work, the aircraft is loaded with mail trolleys, each bay is packed tight with trolleys that are strapped to the floor, then each compartment has a spider net close the compartment off

I do this kind of loading all the time and feel its much safer than carrying a bulk load of loose items or even containers, each trolley is a fairly light weight 80-110KG on average, if the load was not secure correctly im pretty sure some catastrophic would have happened on take off or in the climb

Just toadd that this loading is done with the FO as a supervisor instructing where to put each trolley so I would be very very surprised if it wasn't secured

I'm not type rated on the CRJ so don't jump at my vague information.

I've heard that looking thru the tech log pages there was a problem with the stab motor which had been replaced, perhaps that wasn't the fix. Descent and path down suggest problems with the tail.
Condolances to the families friends and colleagues.

Any news about the FDR readability?

It was said yesterday (article in Norwegian) that the recorders were sent to France a week ago, that two Swedish investigators are currently in France, and that they are confident they will get something out of the recorders within in a week.

AH reports today (1/26) that both recorders have data, are readable, have been read, and a prelim report is expected within 1-2 weeks, following analysis.

Heard rumors of a possible collision with a UAV. anyone has more info?

That would be, to put it mildly, slightly disquieting. . . . . . .

Well that's interesting, what else do you have?
I have to admit the thought crossed my mind but was quickly discredited as highly unlikely due to the remoteness of the area.
Let's hope the FDR has some useful information that will lead to probable cause and not more questions.

I do not have anything more than a rumor that "someone" apparently lost a UAV in the same area at the same time, but nothing confirmed , therefore I was fishing here.
Maybe I should have posted this on the military forum:suspect:
But seen the impact crater , it is doubtful physical evidence will be easily found before the snow melts or if at all, and unless spotted visually before by the crew,I do not think the CVR/FDR are going to help much to validate or invalidate that possibility..

The Swedish board of investigation said they managed to read out the CVR(I Think with help of BEA) and that efter that they have some ideas what happend. Nothing more said yet, they would analyze the FDR first.




I would'nt put that much to the rumour about UAV's.

origin rumors of collision?
 

On the avherald.com link there is a readers comment section and someone calling himself "military" says he has "some inside track", FWIW:

Oh boy, I hope it's not another Night Ship 282 !! (FEDEX 208 feeder crash maybe due to collision with an unknown object)

NTSB: 'Collision With Unknown Object' Killed Mobile Pilot | Aero-News Network

http://www.ntsb.gov/_layouts/ntsb.av...03FA008&akey=1

'Red marks' confound accident investigators | News: Aviation International News

Had never heard of that, but dam its spooky!

Yep, The craziest thing is his sister (If I remember well), a substantial amount of time after the accident on her own recovered more than 700lbs of debris, including the 3 propeller blades from the swamp ! :ugh:That says a lot about the investigators. She is is a 727 pilot, this accident is still a mystery. The pilot was a 9-11 Hero. Very sad.

Thanks Melax, that "Night Ship 282" incident is an interesting read while we're waiting for info from the CRJ CVR/FDR. A mid-air seems unlikely in this case, but strange things happen like the ASG-29 glider vs. Hawker XP800 near Minden, Nevada. No fatalities, but you should see the photos of the Hawker.

Given the number of UAVs in the air and the altitudes they can operate at kind of reminds me of the late 40's and 50's in the US where a number of mid-airs occurred between military and civilian ac due to lack of coordination between the military and CAA. I hate to think of how many military, intelligence, homeland security, local police, state police units may be operating what at this point but I suspect coordination with commercial aviation authorities is not necessarily well established.

Hughes Airwest Flight 706 midair with an F-4 happened in 1971. Thankfully they learned some lessons from it.

This accident happened virtually on the border between Sweden and Norway.
In Sweden, but airspace delegated to Norwegian ACC.


Air surveillance radar systems from both countries cover the area and pictures already released from this.


Nordlys - Her forandrer flyet brått kurs før det styrter


Anyone seeing more than one A/C ?


We might not be 100% sure that the picture is'nt modified but the source is norwegian and the airspace Swedish( from a military view).
If unknown A/C wasn't Swedish, the swedish interceptors would have been launched.
If it wasnt Norweigan, would Norway then edit the picture?


No, there was no other A/C around I say.

That is a transponder based picture. What about a non-squawking machine?

AAKEE : I do not want to add to this UAV rumour, but the picture you posted is from a synthetic display where anything can be filtered out, specific SSR codes and even Primary returns.

What would be interesting to see is what the Swedish Military primary radar displays show. On the other hand a small ,slow moving and mostly composite UAV would not offer much returns.

1. That image in AAKEE's link was released by the Norwegian military.
2. This is the largest UAV in use by Norway: https://en.wikipedia.org/wiki/AeroVironment_RQ-11_Raven
3. This is the largest UAV in use by Sweden: https://en.wikipedia.org/wiki/AAI_RQ-7_Shadow