News Copilot mistakes rudder trim for door lock, rolls 737

[Linguofreak]

The ATW article references the Aviation Herald, which has an article here.

 

[Urwumpe]

Rudder trim can cause a strong roll, but I doubt we are talking about 137° bank angle there. I wait for the official data in that case. more than 37° would alone be dramatic in an airliner and cause a serious loss of vertical lift.

Also, A 737-700 has no fly-by-wire, it only has a glass cockpit and only has autopilot. and the Boeing autopilots are not like the Airbus autopilots, that would tell you "By all due respect Sir, I can't allow you to do this".

http://www.smartcockpit.com/plane/boeing/B737/

I try to find out if moving the trim switch will turn off the autopilot. What I can tell you already is, that the rudder trim switch directly acts on the rudder pedals, changing their neutral position and tries to move them. The rudder pedals are connected by cables directly to the hydraulic actuators. The autopilot and yaw damper system acts on the hydraulic actuators as well, but are both overridden by the pedal inputs

 

[Cras]

I looked in the 737NG FCOM and I could not find anything that says a chance in rudder trim knocks off the Autopilot, assuming we are in CMD, and not in control wheel steering.

CWS may behave differently because it only works through trim to maintain attitude.

I had thought that maybe the bank angle alarm going off may kick off the autopilot, but in the FCOM, the bank angle alert is part of the GPWS, and the GPWS has no means of turning off the autopilot. The bank angle alert turns on at 35 degrees by the way, and repeats itself as the aircraft passes 40 degrees and 45 degrees.

 

[Zachstar]

If this is true this warrants a few weeks suspension with mandatory time in the simulator in my opinion.

While the 737 is a tough craft you simply must not allow events like this to happen. The Airline industry is already fraught with issues over high fuel prices. Incidents like this hitting the news almost guarantees loss of ticket sales for the airlines.

 

[Grover]

you can imagine what came over ATC over the next instant:

"[airliner flight #] you are 6,3 thousand below your assigned altitude... how the hell did you get there?"
"um... there was a slight problem with the... uhh... trim..."
"[airliner flight #] please climb to [assigned altitude] and maintain level flight... surely you noticed that you AREN'T in a high performance stunt craft"
"yea... very sorry about that sir/ma'am it wont happen again "

 

[Urwumpe]

Maybe that was no mistake ... BANZAI!

 

[Linguofreak]

I tried the following in a 777 in X-Plane:

1) Set a "rudder trim runaway" failure to occur on a keypress.
2) Establish the aircraft in stable flight at 30,000 feet.
3) Look away from the monitor and press the failure key.
4) Count to 5 or so.
5) Look back at the monitor, take corrective action.

I tried this several times and found that 5 seconds of inattention (plus one or two seconds more to get my hands back on the stick and start making corrections), combined with a runaway to full rudder trim, was enough to reach bank angles in the range of 90 degrees (and I was expecting to find myself in a roll, and sitting at a computer chair that was not subject to sideways g-forces). A 777 is also larger than a 737, and thus probably slower to roll.

So the situation probably would have gone something like this:

1) Captain arrives outside the cabin door.
2) Copilot looks towards the door and reaches for the door switch without looking.
3) Copilot turns the rudder trim knob instead. Door doesn't open and sideways g-forces (several tenths of a g) are applied as the aircraft begins to yaw and roll.
4) Copilot is thrown off balance by sideways g-forces.
5) Copilot braces himself and turns back towards the control panel.
6) Copilot finds himself in an unexpected roll and takes a second or two to absorb the situation.
7) Copilot begins taking action to return the aircraft to level flight. By this point the aircraft has reached 131 degrees of bank.

 

[N_Molson]

What is surprising is that no passenger got wounded if the plane banked of 137°. It means that the passengers of one side would fall on those of the other side. And the luggages in the lockers overhead could do some harm too. :blink:

 

[Spacethingy]

Does anyone have a 737 in a flight sim/a picture of the cockpit? I want to know if those do buttons are anywhere near each other...

 

[Urwumpe]

As you can see, the respective switches are close to each other, but not similar at all. The big rotary in the center at the bottom of the image is the rudder trim switch. The indicator above it shows the rudder trim position.

The right most switch at the bottom seems to be labelled "FLT DK DOOR". I am not 100% sure it is the right switch, but I would assume so.

EDIT: Yes, correctly identified I would say, this looks similar to this one of a 757:

http://www.biggles-software.com/software/757_tech/airplane_general/flight_deck_door.htm

 

[zerofay32]

It means that the passengers of one side would fall on those of the other side. And the luggages in the lockers overhead could do some harm too. :blink:

Depending on the circumstances, the passengers wouldn't have felt a thing due to g-forces from the roll/dive. And of course, during a flight the overhead bins would for the most part be closed and passengers should be wearing seat belts.

 

[Eli13]

Then I'm guessing the one responsible was not looking at the switch and mistakenly took it for the door lock. How? I have no idea. This is why we use "visual confirmation" people.

 

[Linguofreak]

What is surprising is that no passenger got wounded if the plane banked of 137°. It means that the passengers of one side would fall on those of the other side. And the luggages in the lockers overhead could do some harm too. :blink:

No it doesn't. The g-forces on the passengers still would have been mostly into their seats, and a bit to the side (probably not much more than you'd experience going around a corner in a car, if that, and to the opposite side from what you'd expect). Anybody seated and belted in should have been fine. People standing up would have been in roughly the same situation as people standing up without a handhold on a bus that makes an unexpected turn.

 

[Lambo]

Just thought I'd share another link about this incident, posted the day after the incident in question took place. For those wanting more confirmation about the incident in question.

http://avherald.com/h?article=4428f2f7&opt=0


EDIT: Whoooops disregard this post, seems the link was already posted by Linguofreak. That's what I get for not reading through the thread properly!

 

[FSXHD]

I'm gonna go try this in the PMDG 737 NGX. It's a fantastic simulation. http://precisionmanuals.com/pages/product/ngx.html

 

[Cras]

I'm gonna go try this in the PMDG 737 NGX. It's a fantastic simulation. http://precisionmanuals.com/pages/product/ngx.html

That would give about the best idea of what hard over rudder trim would do. Aside from actually flying the real plane, there is nothing closer than the PMDG NGX.

 

[FSXHD]

That would give about the best idea of what hard over rudder trim would do. Aside from actually flying the real plane, there is nothing closer than the PMDG NGX.

Indeed. I'll post some screen shots of it when I am done.

 

[ky]

I'll try in FS2002 with the damage enabled (yes, people still use it lol).

 

[Turbinator]

This must have been the copilot:

 

[FSXHD]

Sorry folks! I have a bunch of exams tomorrow and I can't fit the NGX simulation in tonight. I will do a proper experiment tomorrow with screen shots and a small write up.