MD80 - ailerons fully deflected at the start of the takeoff roll

[D Beaver]

I was recently on an AA MD-80 departing DFW, sitting behind the wing and I noticed that the ailerons were fully deflected from the time we pushed back until we lined up - no movement whatsoever, which I found interesting. Then we started the take off roll with the ailerons still deflected, which I found scary enough to unstrap and tell the nearest FA (who was not impressed with me moving around during takeoff :eek: ). By the time I had reached him and explained, I noticed the ailerons were now in neutral. I suppose we were doing about 50 kt by this time. The wind by the way was very light and almost straight down the runway.

The captain passed back a message, via the FA, that this was 'normal'. Any MD-80 drivers care to comment on what was happening. :confused:

[ 03 August 2001: Message edited by: D Beaver ]

[xyz_pilot]

I THINK the DC-9/MD-80 have servo tab controls.

[Propellerhead]

Sounds like they 'hang' until enough airflow makes them streamline with the wing (at about 50kts). Does this mean there not hydraulic? Find that pretty hard to believe, and surely hydraulics can hold a surface neutral.

[BigJETS]

Are the elevators of the MD80, and other a/c for that matter, split? I recall watching an MD80 line up; one elevator surface pointed upwards while the other side down. It alarmed me somewhat but I figured it must be acceptable and the a/c following the 80 surely would have noticed. Sure enough, they left quite normally. Makes me wonder though, why the stab would have split elevator movement. I can understand two independent surfaces, but independent movement? Could there be a link with 737 "rudder" hardovers? If the elevs went opposite in flight (if thats at all possible) then couldnt that seem like a rudder thing?

[D Beaver]

Propellerhead
No they were not 'hanging' -they were fully deflected - the port one was up and the starboard one was down.

BigJETS
Your observation of the split elevators seems to indicate a hydraulic issue. Can someone enlighten us?

[ 04 August 2001: Message edited by: D Beaver ]

[spannerhead]

If the md80 is similar to other servo tab controlled a/c then this aileron situation would be quite normal.
The control column directly controls the servo tab only. The deflection of the tab will cause opposite deflection of the aileron. Obviously both tabs deflect in opposition to each other ensuring opposite aileron deflection. Both ailerons however are connected together by a cable system called a bus. So, on the ground and wiggle the column and you will only move the servo tabs. On the ground and move an aileron (by hand or the wind) the opposite aileron will move. Airflow over the aileron during a takeoff roll would bring the ailerons to neutral. The tabs would then control the aileron deflection!! Make sense????

[spannerhead]

bigJETS
The 737 elevators are not split.
I dont know the MD80 but possibly they (the elevators) are controlled similar to the ailerons in my previous post but without the bus cables.
The bus cables in my previous post by the way have a breakout facility so if one aileron physically jams, then a more limited control can be maintained by the remaining aileron (plus the spoilers). If one elevator jams then limited control can be maintained by the remaining elevator. As I say I dont know the a/c but???

[ 04 August 2001: Message edited by: spannerhead ]

[low n' slow]

Sitting with the SAS AOM for the MD 80, section flight controls, I gather that the control wheels are connected indirectly to the ailerons via control tabs. It also says, "A spring type load feel mechanism is incorporated in the controllsystem for each aileron. The mechanism also acts as a control tab centering device". I don't know what a "spring type load feel mechanism" is but I gather that this also works as a centering device for the entire aileron. This I base upon the fact that I've never seen an MD 80 with hanging ailerons as opposed to the elevator.
My guess (and I believe it's a bit far fetched) is that the centering device was inoperative and that the aileron deflection was pure coincidence. Unless, there is as with the elevator, a possibility to generate deflection by giving maximum controll input beyond the control tab deflection (used for before T/O control sfc travel, I think) . However, this also seems unlikely as there was no apparent reason for the pilot to give full deflection. To me it seems as something was wrong.
(don't take this post too seriously, I found the AOM in my dad's bookshelf. The charts looked rather confusing and I'm only just done with my PPL!!! :rolleyes: )
regards/lns

[haamster]

The simplest answer to the question is that the flight controls are not hydraulically actuated. The control column controls the surfaces (aileron and elevator) through control tabs only. When the aircraft is sitting still with no air loads on the surfaces, the control column has no effect on the movement of that surface.

This is the way it is with a DC-9. I believe there is a similar system on the MD-80.

[low n' slow]

I was wrong in assuming that this centering device centers the entire aileron. After having discussed the topic with the owner of the AOM, I now know that the ailerons may hang or look as though being deflected. Just as the elevator (being divided in the middle and "free floating") may settle in low speeds with one up and one down, the ailerons can look as though intentionally deflected. In low speeds, however, to ensure lateral control, there are flight spoilers.
In other words, the elevator and ailerons are controlled by means of a control tab. In "no flow" speeds these control sfcs have their own life. This goes for the the MD 80. The MD 90 however, uses hydraulics for control.
I feel enlightened
regards/lns

[ 04 August 2001: Message edited by: low n' slow ]

[Iain]

Hmmmmm, I really do not think it is safe to get up and go running down to the FA. What happend if there had been a problem and the pilots slammed on the brakes?
Also this took place months ago so why do you keep enquiring about it, especially since you stayed behind and asked the captain personally!

[D Beaver]

Iain,

Of course it's not safe. However, in the course of 30 years of flying as a private pilot and as SLF, I have never been so scared. I thought we were taking off with the ailerons locked :eek: . So what should I do, sit there meekly and watch as we roll inverted?

As for the rest of your comments, I suggest you re-read my post. I said it happened recently, not 'some months ago' and I didn't stay behind to talk to the captain, he passed on a message via the FA, who didn't even bother to mention it to me until I queried him.

After the flight I contacted AA asking for an explanation and received no reply. So I decided to post my question on PPRuNE in anticipation of some informed views. Thanks guys :)

[Iain]

There was also a a guy that kicked in the cokcpit door of a UA jet a while ago in a similar situation.

As for the rest of your comments, I suggest you re-read my post. I said it happened recently, not 'some months ago' and I didn't stay behind to talk to the captain, he passed on a message via the FA, who didn't even bother to mention it to me until I queried him.

I heard a very similar story from some guys a couple months ago, about an AA MD-80 with the exact same condition at DFW so either this is a common on AA MD-80 flights out of DFW, or the story has changed.

[low n' slow]

Or perhaps some research on control tabs.
Servo tab - inteded to lighten the stick force. Control sfc is directly connected to control column.
Trim tab - intended to trim the control sfc and thereby make stick force neutral.
Control tab - provides indirect control to control sfc. There is no direct link between control column and sfc.

Sorry if I seem fussy... :rolleyes:
regards/lns

[D Beaver]

lear 23 and low n'slow

Yes, I know about servo tabs and control tabs.

There didn't seem to be a tab on the aileron that I could see clearly. I'll have a closer look next time I'm on an MD-80

[ 05 August 2001: Message edited by: D Beaver ]

[Final 3 Greens]

I think that this thread shows how dangerous a little learning can be ... and how scary for a PPL - I can sympathise with D Beaver's feelings.

I too have flown privately quite a bit and sometimes get a bit spooked by things I don't understand - e.g. the first time I experienced a flapless take off in an F100 gave me a bit of a surprise! (never seen a jet dop that before)

Anyway, I think that you just have to trust the pros who are ATPLs/type rated, sit back and let them get on with it... otherwise you might cause a real problem.

If anyone has ever read Richard Bach, he says that an aeroplane is divided into two parts, the domain of the passenger (customer is king) and the domain of the pilots.

For us PPLs, we don't belong in either domain and it can be a bit troubling at times!

[ 05 August 2001: Message edited by: Final 3 Greens ]

[Hung start]

haamster and Lear23 are correct as to the mechanics of the MD80. And as some said, the MD90 is a different case, with hyd. powered elevators. So I won´t elaborate on anymore on that.

But I would say that, of course don´t abort a take off from pax. row 22, just because there´s something that seems strange to you as a PPL. BUT lives could on more than one occasion have been saved, had a pax. looked on the wings before takeoff, and seen that they were way too clean. ( A 727 and an MD80 in the US many moons back, spring to mind. Pilots simply failed to extend flaps/slats)
I fly the MD´s myself, and understand if people wonder about the look of it´s controls. Have you been behind one on a windy day, and seen the split elevators?

When the Dash 8-400 started operating with our Commuter detp. I was behind one, for one of it´s first take off´s. Entering the runway, doing flightcontrol checks, the spoilers came up........and seemed to stay up, as they received their take off clearence. I got on the radio to tell the guys. They said " Thanks...but we know, they´ll come down when take off power is applied.
Well, I´ve got to tell you: I didn´t feel any embarresment. None at all. And now I know about the Dash 8.

Guess I´m trying to say; If you REALLY feel something ain´t right, even if you´re "just" a ppl, please tell me.

[haamster]

Well hell, you were never ON my hook. I knew what you meant. But good explanation nevertheless.

[rover2701]

The BAe146 makes use of control tabs on all control surfaces except Rudder. The tabs are controlled from the control column any deflection of the tab causes opposite deflection of the control surface. It is a common sight to see the elevators, when the aircraft is parked, deflected in different directions. :D

[low n' slow]

Well, lear, with that explanation, you're off it no doubt. I believe I wrote the same stuff, just a bit more compacted... :D
To make it clear what I think:
servo tab: inteded to make stick forces lighter when performing a manouver in airflow speeds.
control tab: a tab that controlls the main sfc by deflecting the opposite way. Works like a trim tab, only that it is connected to the control column.
regards/lns

[rover2701]

Lear23 I do not believe that the 146/rj has roll spoilers. The do have ground spoilers and airbrakes, I do not believe that the spoilers operate in the air as roll spoilers. The primary flight controls, Ailerons and Elevators do have control tabs. ;) ;)

[rover2701]

Lear thankyou for pointing out my error. It is 15 years since I did my course and 5 years since my retirement. I get forgetful in my old age. However I checked my course notes and saw the error of my ways. I eat humble pie. :( :(