pacplyer

On another thread we are questioning the possible throttle position of a post accident 747. While this is strictly a hypothetical discussion, we'd like insight into the throttle cable rigging down from the upper deck to the engine. Does it route from the flight deck under the upper deck floor and then exit vertically down main deck stringers to the spars? (which is my memory)

Question arose on the Rumors thread about thrust lever behavior on known in-flight 747-200 separations vs Bogota crash; impact with the ground shearing engines off.

On two in-flight separations that I have accounts of now from colleagues , on engines that "cleanly" detached from failure of the fuse pins: the affected throttle violently slammed to idle as the engine departed while airborne (producing thrust) pulling the control cable with it. (I suspect the engines either dropped straight down or rotated off the pylons in flight.)

Are there any bell-cranks or pulleys in the throttle control routing (or designed/likely failure points in the rigging) that might fail differently if engines ripped off to the rear from impact?
Or fail differently if the upper deck separated and was thrown clear of the burning wreckage? (which is the case here.)

Photos follow.
note also the lack of rotational damage to the core engine fan sections. Does this look strange to you? Wouldn't you expect symmetrical fan blade damage if more than windmilling rotation was present (i.e greater than idle thrust was being produced?)

Here are the photos; kalitta fo

Thanks

gas path

From memory (we're all electric now) The cables run in pairs from the flight deck throttle pack under the floor outboard at an angle to pulleys somewhere above doors 1 L/R, then aft (through cutouts in the u/d floor beams) to roughly inline with the wing leading edge. There is then two change of direction (pulleys) outboard then down (next to the aircon risers) then, there is another change of direction to run along the wing leading edge to the pylons. They then change again to pass along the pylon and terminate in a mixing box that converts the rotary motion into a push-pull motion. From there on its 'teleflex' cable to the JFC.
Personally I think that the final positions of the T/L's resulted from the cables being snagged as the airframe folded on impact.
As for the engine. I would have expected to see more evidence of fan blade damage if it had been rotating (under power) on impact. The engine in the picture may have been shutdown prior in which case it would have just been windmilling.

pacplyer

Very Good description Gas Path. Good memory too. A couple of questions if I may,

1. Where exactly is this mixing box? that converts to teleflex push/pull cable to rotational pulley? Any torque tubes involved?

2. How tight are these cable runs and how critical is their alignment? The reason I ask is we had a problem on some old 74's of T/L's being difficult to move.

So in the case of an in flight separation, all the pulleys and all the cable run stringer/floorbeam cutouts are in serviceable alignment and that's what causes the T/L to slam snap to idle if the engine fuse pins fail and the engine departs.

But in the case of violent distortion of the pylon, would you think teleflex transition (at the mixing box) from push pull to rotational pulley might be somewhat in question?

I wouldn't expect misalignment (initially) along the titanium spar, if that's where the cable run is... used to look up into the drooping slats and see a lot of stuff up there.... are the T/L cables not visible in the leading edge from the ground?; are they in a dry bay behind the spar or something?

Are there any torques tubes involved in any of this?

Not trying to play accident investigator, just a limited experience A&P trying to learn. I realize that the complexities of disintegration of the airframe are certainly not knowable by us, however, it appears to me that a wet earthen berm was hit about halfway through the impact site. Could this account for sudden N1 stoppage? (aircraft skidding along until ground level changes.) I see a great amount of earth and grass packed in one side of the fan section of one of the engines. If, (hypothetically speaking of course,) that were the case: sudden N1 arrest into an earthen berm, would you expect to find resulting damage to the core? Doesn't N1 spin freely of the N2 compressor and turbine exhaust shafts? Say for a JT9D-Q for example.

Thanks for any thoughts guys.

The ground level change appears in the bottom right photo of six (aft clicking, scroll up) :

747-200F down in Bogota ?

pac

ZaaZoo

in the boeing if over 30 pounds of force needed to push throttles then

gas path

The mixing box is located in the pylon. There are no torque tubes involved.
In most cases a stiff throttle could be the teleflex cable as the nylon inner used to break up. Having said that, occasionally the insulation blanket around the L/E pneumatic duct could get wrapped round the cables. (always good to do a full and free check after replacing the duct and/or blankets!!). The cables run along fwd. of the front spar behind the pneumatic duct!).
The mixing box just translates the cable rotary motion around the pulley into a straight push-pull of the teleflex.
Just a guess regarding the T/L and engine separation. If an engine departs the whole of the teleflex would get ripped out of the pylon and possibly, though not by design, that action would snap the T/L back, however in this case as the airframe itself collapsed who knows?. A different scenario all together.
Ooerr! my brain hurts

pacplyer

Thanks Gas Path,

Fascinating machine still to this day. Sorry to wring you brain out over nothing!

pac "Inspector Clouseau" plyer

SUB

Have worked on the 747 for 20yrs, one answer to your question is that the cable run behind the pneumatic ducting just i/b of the engines has what is called cable stops which are installed on each cable (total 8). They are a circular metal fitting that the cable connects to and the assyembly passes through a cable stop bracket which has a micarta block attached to it. There is a specific dimention that is measured from the micarta to the stop which is used during cable rigging. If this measurement is out of limits the theory is that the cable has stretched and should be replaced.

Also in the throttle cable system to decrease friction and increase wear life, the
cables are routed through large diameter pulleys with form fitting
grooves.

Back to the cable stops, they play one more very important job which may help with your questions, if there is an engine seperation the cable stops contact the stop bracket micarta block and the cable shears to prevent the throttle control stand being ripped out of the cockpit and taking out the control and power settings of the other engines (smart hey) hopes this helps.