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AF 447 Thread No. 9

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AF 447 Thread No. 9

Old 15th Aug 2012, 06:43
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Next month I will see Chuck Yeager and Bob Hoover for about the 13th year in a row at the Reno Air Races. I have talked to Bob Hoover because he flew out to Flabob airport to see Art Scholl when I was teaching his aerobatics course. Bob is a great guy. He would have broken the sound barrier except for doing a buzz job just before the event so Chuck got the assignment.
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Old 15th Aug 2012, 11:40
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Turbine D

I wrote:

that the THS movement is not commanded in automatic operation, but operates to reduce the stress on the elevator hinges so it motors to the position that requires no further elevator deflection to maintain the 1g flight path.
then you wrote:

So if a pilot flying level at 350 and Mach 0.80 with a thrust setting of ~85% N1 decides to pull back the sidestick and hold it for a prolonged period of time, some time being all the way back, the elevators will accommodate his command. They will deflect all the way to 30 nose up which it did on AF447. then the THS will begin movement (trimming), as calculated by a computer, to neutralize the pressure on the elevators and also moving up to near the maximum of 14 nose up which it did on AF447.
We would appear to be in agreement that the THS operates to reduce the pressure on the elevators.

That is all I was saying to set the scene. Once it is in that position the THS will operate to attempt to maintain a trimmed 1g flight path. Would you accept that?
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Old 15th Aug 2012, 13:27
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Originally Posted by Ian W
447 however did not enter the stall in the classic straight and level gently slowing down manner. The aircraft was in a rapid climb to above its flight envelope and thrust ceiling converting kinetic energy to potential energy. There is no prestall buffet or normal handling effects if you pull into a hammer-head stall or tail slide this was not far short of that. The resultant loss of aerodynamic lift as the aircraft ballooned over the top with negative g, gave the THS algorithms something perhaps that had never been considered likely.
The aircraft entered the stall on a gently upward sloping flight path of 2.5 degrees, hardly a "hammer-head stall or tail slide". There was considerable pre-stall buffet and never negative g.

Once set up in the stable nose up stall the wrong side of the drag curve in TOGA with a descent speed that was almost as much as the forward speed, there might be insufficient aerodynamic pressure on the elevators even in the down position to get the THS to move. Therefore it would remain fully nose up until (or if) the aircraft responded and started nose down.
Movement of the THS is by hydraulic power and does not depend on "aerodynamic pressure on the elevators" nor on the aircraft going "nose down".
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Old 15th Aug 2012, 14:57
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Movement of the THS is by hydraulic power and does not depend on "aerodynamic pressure on the elevators".....
The question might rather be, "Will the THS move WITHOUT a change in airspeed along the instantaneous flight path, regardless of SS command?"

If it will during some period, under whatever conditions, that would essentially turn SS function additionally into a fancy trim switch and the autotrim into a pitch command augmentation system during this period.

This would not seem to be day-to-day 'normal' autotrim functionality.
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Old 15th Aug 2012, 15:34
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Gums, Yeager is a verycoolguy in personal gab, and impressive, you bet. He is a certified celebrity, and brooks no informality. I have been in conversation with him, and he is a true sky god. He is as sure of himself as some here are insecure. His interest in being paid may come from his lousy pay for flying the
X-1.

Organfreak, I like your take on the Trimmable Horizontal Stabiliser.
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Old 15th Aug 2012, 16:12
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Yeager's favorite airplane was the MiG-19....

I guess he never flew the Airbus.
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Old 15th Aug 2012, 16:19
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If Pete Rose and Dick Butkus can receive pay for an autograph (regularly scheduled at a Caesars Palace near you), then Gen Yeager is welcome to all he can get.
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Old 15th Aug 2012, 16:36
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Hello OK465;
The question might rather be, "Will the THS move WITHOUT a change in airspeed along the instantaneous flight path, regardless of SS command?"
No, the design would not permit this.

The THS can be moved any time using the mechanical system, controlled by the two trim wheels on either side of the thrust lever quadrant.

The THS will not move under electronic control (sidestick or AFS request) unless commanded by the FCPCs. When the THS reaches the FCPC-commanded position the electronic control stops the hydraulic motor.

Operation/Control and Indicating
There are three control modes for the THS:
- autoflight (electrical control)
- manual (electrical control)
- standby (mechanical control)

In the autoflight mode the command signals from the autopilot are sent to the FCPCs. The FCPCs transmit autotrim signals to the electric motors which control the THS actuator.

In the manual mode the command signals from the side sticks are sent to the FCPCs. The FCPCs transmit autotrim signals to the electric motors which control the THS actuator.

In the standby mode the command signals are transmitted mechanically from the control wheels to the override mechanism. The override mechanism cancels the autotrim signals from the FCPCs. It transmits the mechanical command signals directly to the hydraulic motors of the THS actuator. Maximum Operating Load and Associated Maximum Speed (one motor):
18940 daN (42578.81 lbf) 0.2⁰ per second
16950 daN (38105.11 lbf) 0.5⁰ per second
6770 daN (15219.56 lbf) 0.6⁰ per second
Multiply the values by two for two-motor operation

Maximum operating speed is limited by the PTA in the electrical mode to 1 degree per second.

A different way of looking at the THS - Elevator operating relationship is to consider the Lockheed L1011's design. The L1011 did not have elevators or a THS. The entire horizontal stabilizer was the "elevator" and was full-time trim. I no longer have my L1011 FCOM so I can't describe how the trim was calculated when in autoflight but in manual flight, which we did all the time back then, trim was controlled by a small thumb-wheel on the control wheel. When flying manually one could gently tweak the trim as speed changed, otherwise one left the trim alone.

The point is, the THS on an aircraft is a "follow-up" concept, trimming out control forces and satisfying elevator demand, (and making full elevator available at all speeds...QED!). To put it pedantically I suppose, the role of the THS is not in the same category as a primary flight control.

We could think of the THS as "long-term" control and the elevator as "short-term", (I know you know this but for the benefit of those who may not immediately see the difference I include this simple clarification).

General arrangement of the A330 THS control system:





Mechanical trim wheel thrust lever quadrant arrangement:


Last edited by Jetdriver; 15th Aug 2012 at 18:28.
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Old 15th Aug 2012, 16:49
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Angel alternate2B (suite)

Originally Posted by bubbers44
Just remember, automation is our friend, just ask Airbus
thas is the question !

we all know bad automation !! didn't you ???

first and final specifications are very important thing.

If you have two different "~]&=^tempo , for pitch and for roll, as you find it in the alternate 2B law, good automation survey the coordination and mutuel "interruptions" and many other things. and for once human factors are concerned !

Bonin trained the "alternate" law five years ago ! and was it the alternate2B or another alternate law ??? Have the young pilots to be sacrified ?

Airbus has not to say, but to prove, after such an accident.

Questions to all here : who did already fly ALTERNATE2B ?
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Old 15th Aug 2012, 17:03
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Snoop "deepstall"

We accept the old definition of "deeptstall" for hand-flown aircrafts with impossibility to go out of that situation.

But now, the aircraft has been said to have an "apparent static longitudinal stability). That means that the "EFFECTIVE AIRCRAFT" (FCS+A/C) has a "static longitudinal stability". The minimum we have to say, is that our EFFECTIVE AIRCRAFT has an "apparent deepstall" ! with the results BEA pointed.

Automation needs strict definitions and formulae, not litterature and psychology. Processors have algorithms no brain.

Last edited by roulishollandais; 15th Aug 2012 at 17:03.
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Old 15th Aug 2012, 17:09
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The law

Answer is:

It doesn't matter what law is active, as Pilot Flying you have to make the aircraft do what you want it to do!
When the nose goes to 15 degrees above the horizon at FL350, and if you don't want it there, your input should be stick forward untill the nose arrives there where you want it to be.

When Gums had his Leading Edge Flap event in the F-16, all he did was apply the necessary control inputs untill the aircraft behaved the way he wanted it.

The Sea Harrier pilot that lost his radome through a midair collision also suddenly had quite a different aircraft in his hands. Nose cone gone means also pitot tube gone (no more airspeed indication), aircraft no longer streamlined of shape, so lots of noise and vibration, radome and radar parts going into intake do not make the engine happy, etcetera. Quite a startle moment! Still, aircraft brought down safely.
The other aircraft involved, F-16, lost one horizontal tail - aircraft flew on as if nothing had happened: the marvel side of Fly By Wire.

This is not meant to imply that military pilots are always skygods, versus civvie nutcases, but it goes to show that not every possible failure can be practiced in the simulator. Gump already said it: life is like a box of choclates, you never know what you gonna get. Flying is just like life.

Not having practiced "it" in the simulator may mean that the execution may be somewhat less accurate than ideally possible, but the execution should never be a disaster, come on, flying is not that difficult.
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Old 15th Aug 2012, 17:12
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Angel ACARS printer

Who could show us where the ACARS printer was ? No picture found in four BEA reports.
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Old 15th Aug 2012, 17:37
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Printer

ACARS printer is usually at the righthand rear corner of the pedestal.
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Old 15th Aug 2012, 18:00
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roulishollandais;

As per EMIT's comments, the ACARS is bottom right - the paper roll is about 8.5" wide. The 3rd MCDU can be seen to the left of the printer.



Last edited by PJ2; 15th Aug 2012 at 18:01.
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Old 15th Aug 2012, 18:09
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Originally Posted by EMIT
your input should be stick forward untill the nose arrives there where you want it to be.
Agreed, but taking this approach excludes any cause other than pilot/cockpit crew incompetence. It seems painfully obvious that the crew handled the UAS event incorrectly and unprofessionally, but we still need to understand why they didn't put "the stick forward until the nose arrives there where you want it".
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Old 15th Aug 2012, 18:47
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Is it possible that the PF wanted the nose at 15 degrees?
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Old 15th Aug 2012, 19:07
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Originally Posted by HazelNuts39
Is it possible that the PF wanted the nose at 15 degrees?
Of course it is possible, but was it likely? Somewhere deeply hidden inside training, culture, cockpit display, and or flight guidance instrumentation, lies the answer.

On the surface, it certainly seems that both Bonin and Robert wanted it that way most of the last three minutes.
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Old 15th Aug 2012, 19:09
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Is it possible that the PF wanted the nose at 15 degrees?
As per the first memory item he would have executed regarding pitch and power in the UAS scenario from his original UAS training, (which was right after takeoff)? Yes, I think it is possible.
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Old 15th Aug 2012, 19:57
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PJ2
As per the first memory item he would have executed regarding pitch and power in the UAS scenario from his original UAS training, (which was right after takeoff)? Yes, I think it is possible.
And later on it is possible too, they wanted to arrest the descent.

Emit
When the nose goes to 15 degrees above the horizon at FL350, and if you don't want it there, your input should be stick forward untill the nose arrives there where you want it to be.
When the aircraft is descending, and you want it to return to the assigned FL, you have to climb. For that you have to raise the nose (SS NU) and maybe you have to add power (TOGA). If 5 pitch is not enough, lets use more........

Last edited by RetiredF4; 15th Aug 2012 at 19:58.
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Old 15th Aug 2012, 20:03
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Clearly, they missed the old adage-- push forward, the houses get big; pull back, they get small; pull back some more, the houses get big again.
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