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finncapt
9th Jan 2017, 10:03
Not sure what the program is called in English and mods feel free to move this if it's in the wrong forum.

I was watching this program and the featured accident was a Fedex MD11 at Narita.

The conclusion of the cause of the accident was, according to the program, pilot error - for flaring too late and incorrect bounce recovery.

Earlier in the program they quickly glanced over the fact that the MD11 has a smaller rear tail and fin assembly - a fact that I was not aware of.

My general understanding is that when a stretched model of an aircraft is produced it quite often requires larger tail surfaces.

I wonder if anyone would care to comment.

Doors to Automatic
9th Jan 2017, 10:25
Although technically it was pilot error, I often think this is the easy option when it has come to diagnosing the cause of the numerous MD-11 crashes.

I don't recall any other aircraft have such an appalling landing-related crash record and I am glad it is no longer in passenger service.

DaveReidUK
9th Jan 2017, 10:35
Earlier in the program they quickly glanced over the fact that the MD11 has a smaller rear tail and fin assembly - a fact that I was not aware of.

The MD-11 has a smaller horizontal stabilizer than the DC-10. AFAIK the fin/rudder is identical on both.

My general understanding is that when a stretched model of an aircraft is produced it quite often requires larger tail surfaces.That doesn't sound intuitive. On a stretched aircraft, the tail control surfaces have a greater moment arm about the CofG, so the reverse ought to apply.

A good case in point was the shortened 747SP, which required a larger fin/rudder than the regular 747 because of its reduced length.

finncapt
9th Jan 2017, 11:46
Yes Dave, I was having a non-thinking moment.

westhawk
9th Jan 2017, 12:12
Smithsonian channel will air the MD-11 at Narita landing accident episode of Air Disasters next Sunday evening. (Jan 15)

Based upon what I've read about the MD-11 previously, The reason for reducing the size of the HS was said by many to be related to an attempt by MD to improve the specific fuel consumption performance by reducing drag. It could also be argued that being further from the CG on the longer airframe, less area would be required. Even so, it never achieved the specific fuel consumption performance MD said it would. That was likely one of the factors contributing to it's less than stellar market performance.

FedEx pilots on other forums have stated that the MD-11 can be a handfull in the flare compared to the DC-10, particularly when gusty. Gotta be right on speed and attitude at touchdown. Not as much wiggle room as other large jets apparently. Somewhat "less forgiving" is another description I've seen.

Flare a little high or fast it levels off, then a sink rate develops and the pilot reacts with a pitch-up input just as the mains smash the runway. With the yoke back, it leaves the ground and the pilot reacts with a big push. Now the pilot's inputs are out of phase with the aircraft pitch attitude and motion. Classic Pilot Induced Oscillation. I'm more accustomed to seeing this with training and pleasure aircraft, usually Cessnas. Many people may know the phenomenon as porpoising (https://www.youtube.com/watch?v=4rwhaHIQrcU) when it occurs during landing. It often increase in magnitude each cycle and continues until something breaks or it uses up enough energy. Going around is often the best cure.

In the case of the FedEx MD-11, a wing structure failed in overload and sheared off from the airframe. With the remaining wing still attached and producing lift, it rolled the airplane over on it's back. For comparison purposes, the BA 038 B-777 at Heathrow overloaded the fuse pins attaching it's MLG to the trunions, allowing the gear to be pushed up through the dry bays instead of overloading the wing structure. This is a Boeing design feature not utilized on the MD-11.

So it can certainly be argued that design features played a significant part in this accident. A counter-argument might be that a pilot more on their game would react correctly to prevent the hard touchdown in the first place. Each of these arguments seems to have merit. And there is little doubt among those who fly it that the MD-11 will punish any mishandling in the landing phase more quickly and severely than the DC-10.

Meanwhile, just a little less than all of the pilots with experience in type have gained that experience without serious incident. Go figure.

EstorilM
9th Jan 2017, 14:08
Does the wing size in relation to the aircraft weight play a large role in the flare behavior? Common sense would seem to dictate so, but then again aerodynamic performance and behaviors are obviously about a thousand times more complicated than meets the eye.

Still, the A330 with a relatively low wing loading, is known to "float" or want to stay in the air, while the "clipped wing" / larger / heavier mods to the MD-11 would tend to imply the opposite (which is a known design feature of the aircraft) however the opposite landing tendencies seem to apply as well. I'd imagine wing loading starts to play a large role when ground effect kicks in.

Anyways, as the others have said - "tail surfaces" control totally different "dynamics" of the aircraft. The hstab can be "clipped" to reduce drag, however it's opposing force to the wing will be reduced (at least, proportionately so) - obviously in level / normal flight this is not an issue. At first glance you'd be able to infer slightly diminished pitch control authority, though I'm sure they tuned the controls to "feel" almost the same.

However you can't dodge physics, so I imagine at low speeds and near stall / on approach or flare, the impacts of shrinking the hstab have some unforseen impacts as well.

Rudder / tail is totally different - that remained almost the same - as others have said, it's a function of length mostly (which is also why the short but HEAVY A380 has a massive vertical stabilizer.)

WindSheer
9th Jan 2017, 19:43
Check out the a318 tail v the a320......

mary meagher
9th Jan 2017, 20:00
A few years ago a glider pilot got distracted in rigging before an airtow....
(wasn't me)...the controls not attached to the elevator. initially on tow the glider climbed dangerously high behind the tug, so the pilot released.

The glider then entered fugoid ...All by itself. All the way down to the ground, and at arrival point just happened to be in a suitable attitude. On a suitable farmer's field.

Could this take place in larger aircraft? Was the glider technically stalled?

Concours77
9th Jan 2017, 20:21
"attaching it's MLG to the trunions, allowing the gear to be pushed up through the dry bays instead of overloading the wing structure. This is a Boeing design feature not utilized on the MD-11."

(BA038)

This feature created the only serious injury to a passenger, as I recall. The gear rolled up and fractured the gentleman's leg, badly.....on the right side of the aircraft......

As to Narita, a case can be made that McD over engineered the mains and the NG. Had the mains collapsed the aircraft would likely not have rolled, due the broken port side main spar.... On the second nose plant, the gear held, and the nose rebounded to about a sixty degree angle? This contributed to the aircraft's completed inversion.....and all hope lost of a crew survival...

There is strong, and there is "too strong"?

DaveReidUK
9th Jan 2017, 20:37
Could this take place in larger aircraft?

Yes, several fatal accidents have occurred where damage to flying controls has led to phugoid oscillation in types including 747, A300 and DC-10.

Was the glider technically stalled?No, AoA remains fairly constant during a phugoid. It's pitch angle that oscillates.