video of 737 pilot during difficult short final

Compare the last 100' (1:30) of this video to the OP's video. You can see the similarities given the conditions. Could the pilot in the original video be over controlling? Maybe. I definitely won't jump to that conclusion as others seem to have done.

 
Larry in TN said:
On DC9s (all the way through the MD80s, MD90s, and the B717) the only powered control surface is the rudder (though there is a powered actuator used to move the elevator toward nose-down when it doesn't respond in a deep stall condition). Even the much larger DC8 had an unpowered elevator with basically the same control-tab system.
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Funny to me story: I had just passed my PP check ride, and was riding an MD88 somewhere, can't remember where, and had a window seat next to the port wing. At the gate, I look out and am surprised to see the left aileron in the full up position. I look right, and I'm aghast to see the starboard aileron full up as well. So, being a new PP and JUST KNOWING how control surfaces work, I let a passing attendant know of my concerns. Shortly after, the FO comes out with a big smile on his face, and explains how the servo tab ailerons work on the MD88, and said it was windy at the gate, and winds blew the ailerons up. He assured my they would drop into position as the plane accelerated for takeoff.

I was skeptical, as the surfaces remained up during taxi, but damn if he wasn't right, they fell into place on the takeoff roll, and the flight was fine.
 
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Larry in TN said:
Control tabs, not trim tabs. Also called a servo-tab. https://en.wikipedia.org/wiki/Servo_tab

On DC9s (all the way through the MD80s, MD90s, and the B717) the only powered control surface is the rudder (though there is a powered actuator used to move the elevator toward nose-down when it doesn't respond in a deep stall condition). Even the much larger DC8 had an unpowered elevator with basically the same control-tab system.
Click to expand...
The KC-135/B707 was the same way. No powered flight controls, except for the rudder. The ailerons and elevators were moved by control tabs through the first 2/3 of yoke throw, the last 1/3 you were moving the actual flight control surface. On the ground we run do a full flight control check as part of the preflight, and you could definitely tell when you got to that "stop" and started moving flight controls. In flight, for all practical purposes, all you ever moved was the tab.

Bill Jennings said:
Funny to me story: I had just passed my PP check ride, and was riding an MD88 somewhere, can't remember where, and had a window seat next to the port wing. At the gate, I look out and am surprised to see the left aileron in the full up position. I look right, and I'm aghast to see the starboard aileron full up as well. So, being a new PP and JUST KNOWING how control surfaces work, I let a passing attendant know of my concerns. Shortly after, the FO comes out with a big smile on his face, and explains how the servo tab ailerons work on the MD88, and said it was windy at the gate, and winds blew the ailerons up. He assured my they would drop into position as the plane accelerated for takeoff.

I was skeptical, as the surfaces remained up during taxi, but damn if he wasn't right, they fell into place on the takeoff roll, and the flight was fine.
Click to expand...
Yeah, on larger airplanes more often than not the flight controls aren't connected to each other. It's odd (but not unheard of, like you pointed out) to see both ailerons deflected the same direction. More often than not what you'll see that looks "funky" is a split elevator where one side is up and the other down.
Like this:
SplitElevator.jpg
 
Larry in TN said:
On DC9s (all the way through the MD80s, MD90s, and the B717) the only powered control surface is the rudder [...] Even the much larger DC8 had an unpowered elevator with basically the same control-tab system.
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The joke is that DC stands for "direct cable"

Sluggo63 said:
Yeah, on larger airplanes more often than not the flight controls aren't connected to each other.
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More often than not they are also independently actuated to give some measure of redundancy. If one elevator jams or fails the other is still available for some amount of pitch control.

Nauga,
and the dancing elephants
 
denverpilot said:
McD did some very interesting and odd things.
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If you're referring to the control system stuff being discussed, nothing presented here is unique to Douglas airplanes.

Nauga,
running up a servo tab
 
denverpilot said:
McD did some very interesting and odd things.
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Douglas Commercial (the source of the DC designation), actually. Long before the merge with McDonnell.

Back then the designers used engineering finesse as they didn't have the luxury of the brute technological force that we have today. Hydraulic systems were not nearly as reliable as they are today so you would avoid relying too much on them when it could be avoided.
 
Have to wonder what the yoke action would look like on a coupled approach in the same conditions?
 
Bill Jennings said:
So, being a new PP and JUST KNOWING how control surfaces work, I let a passing attendant know of my concerns. Shortly after, the FO comes out with a big smile on his face, and explains how the servo tab ailerons work on the MD88, and said it was windy at the gate, and winds blew the ailerons up.
Click to expand...

Don't feel too bad - back in my MD-80 days I've had a self proclaimed "commercial pilot" come forward after the flight and accuse me of putting everyone's life in danger by flying around with only one engine running. He was seated such that he could look back into an engine and swore that it remained shut down for the entire flight. I began to explain, but he didn't want to hear it, and walked off saying that he was planning to write a letter to the airline. Which is kind of funny given who I was flying for - management would read that letter and think, "Saving gas by flying around on one engine? What a GREAT idea!!!" :)
 
Let'sgoflying! said:
Have to wonder what the yoke action would look like on a coupled approach in the same conditions?
Click to expand...

Can't comment on the 737, but in the MD-80, it's basically the same. Right before disconnecting the AP, I'd stare at the yoke and think "Great, now *I'm* going to have to do that!" There are some guys that take pumping the yoke to levels I don't think are completely necessary, but there's definitely a lot more movement than what you'd think.
 
Let'sgoflying! said:
Have to wonder what the yoke action would look like on a coupled approach in the same conditions?
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In the 737 the autopilot tends to overcontrol is such conditions. Those conditions exceed the limitations for a autoland, FWIW.

The DC9s I flew were the pre-MD series with analog autopilots. They didn't do well at all in such conditions.
 
Bill Jennings said:
OK, I've noticed this "funky elevator"[1] on numerous taxiing DC-9/MDxx birds, whats the deal, as it always looks like it does above. Starboard side up, port side drooping.
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The two elevators are not connected. They are free to move independently so they often end up at different angles as the wind hits them differently while on the ground.
 
Bill Jennings said:
OK, I've noticed this "funky elevator"[1] on numerous taxiing DC-9/MDxx birds, whats the deal, as it always looks like it does above. Starboard side up, port side drooping.

Why?
Click to expand...

Bill, there is no control cable connecting the elevator to the yoke control. With no steady airflow over the elevator, it kind of does its own thing until airspeed on the takeoff run moves it into the correct position.

The yoke is direct connected to a control tab (kind of like a trim tab) on the elevator surface. At takeoff speeds and higher, the airflow over the elevator control tab moves the elevator to the position desired by the pilot.

See posts 37 and 39.

-Skip
 
nauga said:
If you're referring to the control system stuff being discussed, nothing presented here is unique to Douglas airplanes.

Nauga,
running up a servo tab
Click to expand...

True. They just seemed to do a little more of it. Nothing that rises to the level of "a big deal". Just know your systems. :)
 
Any of you commenting on this control input ever land a short coupled tail wheel aircraft like a Pitts? On landing you will have the rudder lock to lock both directions many times during every landing, just as quick as you see here or even faster. If you don't you end up tiptoeing through the daisies and if you keep the input in any longer then an instant (another words if you see the plane changing direction) you end going down the same tippy toe path. Must have Happy Feet for short coupled biplanes!
 
Spotter626 said:
Any of you commenting on this control input ever land a short coupled tail wheel aircraft like a Pitts? On landing you will have the rudder lock to lock both directions many times during every landing, just as quick as you see here or even faster. If you don't you end up tiptoeing through the daisies and if you keep the input in any longer then an instant (another words if you see the plane changing direction) you end going down the same tippy toe path. Must have Happy Feet for short coupled biplanes!
Click to expand...
Excellent analogy. Same concept.
 
Spotter626 said:
Any of you commenting on this control input ever land a short coupled tail wheel aircraft like a Pitts? On landing you will have the rudder lock to lock both directions many times during every landing, just as quick as you see here or even faster. If you don't you end up tiptoeing through the daisies and if you keep the input in any longer then an instant (another words if you see the plane changing direction) you end going down the same tippy toe path. Must have Happy Feet for short coupled biplanes!
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That's like comparing cranberries and watermelons.

Not even the same kind of thing. And yes, I fly a short coupled tailwheel.
 
Bill Jennings said:
Funny to me story: He assured my they would drop into position as the plane accelerated for takeoff.

I was skeptical, as the surfaces remained up during taxi, but damn if he wasn't right, they fell into place on the takeoff roll, and the flight was fine.
Click to expand...

And thus you lived to tell the story.

<grin>.
 
I posted my skepticism earlier in this thread, but I've changed my opinion. I did a checkride for rental in a 172 today in a crazy gusty crosswind. I was a stranger to the instructor, so she kept her hands on the yoke for the first landing, and my control inputs to keep the plane on track were so drastic and quick that her arms kept catching my eye they were flailing about so much to stay on the controls. It looked a lot like the video posted. I just never noticed it until I saw someone else trying to keep up.
 
Salty said:
I posted my skepticism earlier in this thread, but I've changed my opinion. I did a checkride for rental in a 172 today in a crazy gusty crosswind. I was a stranger to the instructor, so she kept her hands on the yoke for the first landing, and my control inputs to keep the plane on track were so drastic and quick that her arms kept catching my eye they were flailing about so much to stay on the controls. It looked a lot like the video posted. I just never noticed it until I saw someone else trying to keep up.
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Right. A C172 feels turbulence exactly like a B737.
 
Kritchlow said:
Actually no i didn't. Perhaps I didn't read it close enough.
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I'll help you out. I have a new perspective now and can see how it's possible when before I couldn't see it.
 
Salty said:
I'll help you out. I have a new perspective now and can see how it's possible when before I couldn't see it.
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No perspective other than "push down for bigger house", "pull up for smaller houses" should be associated between a C172 and a major airliner.
 
Why is his upper body moving different directions than his arms? Not buying it. Looks fake.
 
Kritchlow said:
No perspective other than "push down for bigger house", "pull up for smaller houses" should be associated between a C172 and a major airliner.
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I'm not sure whether to address the nonsensical notion that there are no similarities or the fact that my revelation has nothing really to do with flying per Se, and you still don't get it, so I'll just say, "you are a god, and I am nothing" and we can both have a good day.
 
Sluggo63 said:
I think what everyone loses sight of is that these planes have quite a bit on momentum behind them. In gusty crosswinds, inputs have to be rather quick and in some cases, extreme. Once you see the nose start to rise or fall, you're already late. You need a rather significant input in the opposite direction to stop the trend, then back off to what you think is normal. That's why you're seeing what looks like "pulsing" of the yoke/wheel. The input you're seeing is more than likely a movement to stop an unwanted trend before it gets worse, then the input is taken out and repeated as necessary. This is more prevalent in older, cable-pully aircraft. When I flew the 707, this is what it would look like in the on a gusty crosswind day. It was like driving a truck with no power steering. Inputs needed to be rapid and aggressive to keep the nose pointed where you wanted to. In the MD-11 and 777, you needed less amplitude to your corrections, but the same "impulse" type corrections. These are big airplanes and little tiny corrections aren't going to cut it when the nose is tracking all over the sky.
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You have it down pat Sluggo. Proper control input in gusty conditions.
 
Notice how all of these films in the cockpit are of foreign carriers? It’s generally not a good idea to put a video on Utube of one landing a U.S airliner. I’m not saying it’s never been done, just that it may lead to an ‘investigation’.
 
It is kinda like landing a conventional gear aircraft. Your rudder inputs need to be rapid, forceful, and back to neutral quickly.
 
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