DC-10/MD-11 Control cabling.
 

Does the DC-10/MD-11 autopilot utilize the cabin floor routed control cables to operate the (tail) control surfaces? Or was it a different system, possibly above the cabin using electrical signals? I would usually look at the manual but I can't find any online in pdf format to fathom the answer to this question, which to fellow oldies/anoraks will know why I am asking.

I'd have to dig out the MD-11 schematics to be certain but my recollection is that, unless LSAS (Longitudinal Stability Augmentation System) is shut down or failed, the elevators are controlled by electrical signals from the Flight Control Computers (FCC) to the elevator hydraulic rams. This would be the case whether AP is engaged on not. When AP is off, manual column force is sensed by the Control Wheel Steering sensors in the control wheel hubs. Feedback from the rams to the control column is by the mechanical cables which become primary if LSAS/CWS/AP becomes inoperative.

I didn't work on DC-10 but I assume its CWS worked in a similar way. (But no, I don't know why you are asking.)

No idea, why you are asking it like it is a big secret. 5 second search on google:

https://en.wikipedia.org/wiki/Turkis...nes_Flight_981

cabin floor

No secret, just didn't want to clutter the question. I am aware of the Wikipedia article (having initially started the article back in '03'ish) - I am also familiar with the entire accident report and all the published books and material as well as contact with some of the authors.

I am of course aware the cables routed through the cabin floor, hence my question.

There has never been any mention/suggestion that re-engaging and flying through the A/P (after it initially disconnected) might have averted the disaster, but that is what a DC-10 IP wrote he was told back in '74, in case of this decompression happening - control could be maintained through the A/P. I am curious if he was accurate in that statement.

Very interesting, so I assume the cables were not employed if the A/P was engaged? And the control wiring could have run above the cabin.

Not true. The cables back drive the columns and yokes when AP is engaged. I don't recall that the design considered what would happen if the mechanical control cables failed with AP engaged. Closed loop AP control used LVDT feedback of each ram position and I don't think it would care if the mechanical cables were broken.

I have no knowledge of where the AP electrical control signals were physically routed. I am sure that there would have been separation of the 4 channels for damage tolerance but I don't know where each of the cable runs was located.

If researching DC-10 flght controls the MD-10 may be a better basis for comparison than MD-11.

Okay, didn't read your post accurately, because of the way you phrased it. What you should be asking is: "Where are the AP servos located".

For MD-11 elevator hydraulic actuators are in the horizontal stab. Control is divided between the two flight control computers with FCC-1 driving right outboard and left inboard and FCC-2 driving right inboard and left outboard elevators. FCC control input drives the actuator mod pistons and feedback of mod and ram piston positions is provided electrically to the FCC.

I would expect DC-10 to be similar architecture except that the two MD-11 digital FCC are replaced by analog pitch and roll computers.

That definitely sounds like the AP controls the actuators directly, so control would be independent of the control cables that are connected to the cockpit. And if the signal wires for the AP are not routed through the floor like the control cables, OPs story could have merit.

Apologies.

Some good information on DC-10 here - https://tinyurl.com/39kjf52s

There is an "Automatic Flight Guidance System block diagram" included in the doc "Douglas DC-10F familiarization" (linked in third post to that thread).

No Prob. I should apologize. That was phrased bad by me.

If you really want detail of the mechanical elevator control system download IPC_ATA-25-34.pdf which is linked later in the same thread. It's a searchable PDF and "ELEVATOR HYDRAULIC ACTUATION" shows the elevator hydraulic actuators in detail. A search for "Elevator" finds all the parts between the control column and the actuators. I have not yet found similar detail for the flight guidance system actuator interface. It should be in ATA chapter 22.

Thank you! Excellent resource.