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AF447 Thread No. 3

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AF447 Thread No. 3

Old 7th Jun 2011, 19:00
  #1561 (permalink)  
 
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lomapaseo:

I get the jest! However, perhaps I worded my question inaccurately. I know the occupants of AF447 can tell us nothing. What I was trying to get at: if the passengers and, most importantly, the flight crew "felt" this rapid descent would it not make sense that the PF was applying stick up as he felt this rapid descent?

PS: don't need a bike to launch off a cliff. I'm fully cognizant of the feeling of rapid descents, having spent so many years jumping out of perfectly sound air craft!!!!!!
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Old 7th Jun 2011, 19:08
  #1562 (permalink)  
 
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What do you feel when you're descending in an elevator?
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Old 7th Jun 2011, 19:14
  #1563 (permalink)  
 
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Cool

Hi,

What do you feel when you're descending in an elevator?
I feel something when the elevator go in motion (and I feel I go down or up)
It's just a very short feeling as the most of the travel (up or down) is made at constant speed (no acceleration or deceleration)
I have also a short feeling (of go up or down) when the elevator stop
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Old 7th Jun 2011, 19:18
  #1564 (permalink)  
 
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Greybeard:

When I'm in an elevator which is going downwards I feel exactly that: descent.
Conversely, when I'm in an elevator which is going up I feel exactly that: ascent.

But a descending elevator does not normally descend at 10,000 ft/minute.

I just can't get my mind around an aircraft descending at 10,000ft/minute and no one
felt that. I'm not doing so out of any morbid or macabre reasoning. It just seems to me that at such a rate of descent that the PF might have felt the same and applied back pressure on the stick.

Then again, perhaps I don't fully understand the aerodynamics involved here.
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Old 7th Jun 2011, 20:01
  #1565 (permalink)  
 
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One thing that has bugged me is that the flight control system very quickly gave up control when it lost airspeed information. In these degraded modes, I can understand dropping off the autopilot, but going to a degraded mode just because you lost two airspeed sensors is silly.

Others have theorized that using GPS/INS inputs could have been substutited for the missing pitot information, but actually there was, most likely a more simple solution and it is/was actually there all the time.

In every FADEC engine I have seen, the engine control requires total pressure at the engine inlet (so called PT2 sensors). I don't know what PT2 sensors are on the GE engines on the A330, but I'd pretty much bet that EACH engine has at least two of them. PT2 sensors are measuring the same thing as a the pilots pitot probe and the information could be readily suppled over the data bus to the aircraft. If the engine PT2 probes would have lost data in this event there would have been engine fault codes and a loss of engine control (engine FADEC failure), and that didn't happen. Since it didn't it is pretty safe to say they didn't have a loss of PT2 data in the FADECs.

It very likely that there were at least 4 or more total pressure probes that could have supplied sufficient information to keep the flight control system happy while the primary system sorted itself out.

Yes I know full well there are going to be certification issues with this kind of system. Probe life, reliability, and high angle of attack calibration are all issues, as well as issues related to continuing airworthiness if probes are changed from one type to another.

But all of that is paperwork. If they really wanted or needed that information, it was/is there all the time.

This goes back to what level of redundency do you need to be safe, but really, the extra data was most likely there all the time, all it would have taken is a programming change and the issue would never have arisen.

Maybe somebody with intimate knowledge of the CF6 in this installation can chime in on how the engine gets it PT2 information, but my guess, based on the dozen or two engines that I am most familiar with is that the data is out there.
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Old 7th Jun 2011, 20:22
  #1566 (permalink)  
 
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Originally posted by AlphaZuluRomeo ...
The ABNORMAL ATTITUDE LAW is triggered if (non exclusive list):
- the [measured I presume] speed is below 60kt
- the AoA is above 30°
Per the BEA note, at each time after the beginning of the final descent, one of these two conditions was met.
So the ABNORMAL ATTITUDE LAW should have triggered, meaning the auto-trim was lost, hence the THS stayed "stuck" at 13° value.

My question for those in the know : Does the ABNORMAL ATTITUDE LAW activation also trigger a message indicating to the crew that the auto-trim is unavailable ?
In the first instance, you should be made aware of a Flight Global report attributed to the BEA.

Secondly, the FCOM provides the following statement on ABNORMAL ATTITUDE LAW -
An abnormal attitude law in pitch and roll is provided, if the aircraft is in flight and in any of these conditions:
- Pitch attitude > 50° node up or 30° nose down
- Bank angle > 125°
- Angle of attack > 30° or < - 10°
- Speed > 440 knots or < 60 knots
- Mach > 0.96 or < 0.1
The law in pitch is the alternate law without protection (except load factor protection) and without auto trim. In roll, it is a full authority direct law with yaw alternate.
After recovery, the flight laws are:
In pitch : Alternate law.
In roll : Direct law with yaw alternate.
First reading of the above leads one to believe that each of the conditions is mutually exclusive, but if the Flight Global report is to be believed, that is not the case. The new interpretation is that the conditions are mutually exclusive PROVIDED all the ADRs haven't been rejected, but should all the ADRs be rejected, then an inertial upset involving either of the first two items will revert the aircraft to ABNORMAL ATTITUDE LAW.

If this was the case, the MANUAL PITCH TRIM ONLY was not displayed, as auto trim was still available.

Don't take it all as "gospel", as that is not what the FCOM currently says.

EDIT :: See post #1571 by A33Zab for details.

Last edited by mm43; 7th Jun 2011 at 20:47.
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Old 7th Jun 2011, 20:36
  #1567 (permalink)  
 
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Originally Posted by rgbrock1 View Post
I just can't get my mind around an aircraft descending at 10,000ft/minute and no one felt that.
I suppose no one does to the full extent. See e.g. http://www.faa.gov/pilots/safety/pil...a/SpatialD.pdf
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Old 7th Jun 2011, 20:36
  #1568 (permalink)  
 
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Originally Posted by gums View Post

How did the THS get trimmed to near the limit?
To me it seems there are two aspects to Auto Trim.
One is the normal behaviour of 1g Trim.

So the system tries to trim for 1g vertical acceleration.
This can theoretically only happen if the stick is neutral, because any Nose Up Stick Input means commanding > 1g.
Only when commandig 1g (i.e. Stick neutral) the system can know what the target FPV is where it is supposed to maintain 1g.

But that doesn't explain the 13° NU.

Somehow I've got a feeling it is a side effect due to the fact that after continuous NU the Aircraft started to stall and actually fell below 1g which the system tried to compensate by applying NU THS trim.

Somewhere there was a statement that the Autorim tries to support the elevator in case the latter alone is not able to achieve the requested attitude by the PF. I rather tend to think that the latter is a somewhat awkward description of what I mentioned in the preceding paragraph.

Last edited by henra; 7th Jun 2011 at 21:02.
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Old 7th Jun 2011, 20:37
  #1569 (permalink)  
 
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Air France Salvage Mission Ends - BBC

BBC News - Air France crash salvage mission ends
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Old 7th Jun 2011, 20:40
  #1570 (permalink)  
 
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ADIRU

Went into the ADIRU today:

ADIRU computes AOAi from sensor resolver cos. and sin. and calculates
AOAc as function of AOAi, FLAPSLAT CONFIG and Sensor position(LH/RH)

If CAS < 60 Kts AOAi & AOAc are set to 0° and SSM (System Status Matrix) is set to NCD (No Computed Data),
this is also valid for TAS 0 Kts if CAS < 60

If CAS < 30 Kts it declares itself invalid and outputs 0 Kts and NCD.

These parameters are send to 8 similar ARINC output busses.
Bus 5-8 are reserved for the engines only. (Bus 7-8 are not used on A33).
Note: GE engine provides its own Air Data, A/C ADR is only used as backup.

PRIM 2 & 3 receives data by ADR's bus 2, PRIM 1 by ADR’s bus 3.

Note: In Back-Up Speed Scale (BUSS) equipped A/C AOA is send via IR bus
Note: Couldn't find if a SSM NCD is taken in account by PRIM but most probably it will.

In the 1st BEA report the unreliable speed logic is explained.

The PRIMs trigger a monitoring process when one of the speeds decreases more than 30 Kts (in 1 sec.) compared to the median value.
The PRIM opens a monitoring window during which it operate in ALT 2 Law, the rudder deflection limit is frozen but associated message is inhibited.
At the end of the monitoring window, if the diff. is less than 50 Kts the PRIM returns to normal law.
If not it remain in ALT 2 LAW and at that time the F/CTL RUD TRV LIM FAULTmessage is shown.
Outlier ADR is rejected and remaining control is on median value of the other 2 ADR’s
(Stall warning is generated by highest AOA and not the median value)
This means actual AOA could be indeed 40° while not triggering ABNORMAL ATTITUDE LAW due to a median AOA value below <30° as already mentioned in the BEA ‘leak’.

If 2 ADR outputs are erroneous, but different, and the remaining ADR is correct OR all 3 are erroneous but different:

The AP and A/THR disconnects and if disagree last for more than 10s, the PRIMs trigger the NAV ADR DISAGREEmessage.
ALTERNATE 2 LAW become active and latched for remainder of the flight.
(AP and A/THR can be re-engaged if ADR output was only transient.)

Active PRIM could in this case reject the correct ADR data.
That's why crew need to perform the unreliable speed Indic/ADR check QRH procedure and isolate the ADR in error. (Thus it will not be used for faulty PRIM input & indication).

The PF slight but consistent nose up command is a +G request to the PRIMs, the A/C feedback by means of accelerometers however results in a -G.
PRIM deflects elevator and due to negative result drives the THS all the way ANU.

Unfortunate left unnoticed because any hand on the trim wheel had cancelled the PRIM THS orders.

Last edited by Jetdriver; 8th Jun 2011 at 02:31.
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Old 7th Jun 2011, 20:40
  #1571 (permalink)  
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What do you feel when you're descending in an elevator?

This question is not fit for purpose unless a time frame is defined.

In a true equilibrium state you will feel nothing.

Rate of change of descent is quite another matter.
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Old 7th Jun 2011, 20:44
  #1572 (permalink)  
 
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Originally Posted by A33Zab
Tactile feedback
JD-EE:

In normal situations the 'feedback' will be noticed by PNF.
If PF SS input is 1G climb (ANU), PNF will experience a 1G climb and knows PF pulled the stick (not to the max).

What you are suggesting is an interconnection with both SS (Bus bar or by Electric synchronisation) and in abnormal situations you want to disconnect this synch.

A lot of engineering ahead for a feature which will be of -no use- most of the time.

There is a visual indication of resultant SS inputs on PFD on ground.

mm43 post: AF447 Thread No. 3
And as Dozy has commented, it's more hardware to fail. And failures, without very clever mechanical design, could be very bad failures.

In my sour moods I start asking, "Why does the A330 have any pilots at all?" Then two things come to mind. That would require more computer than was available in '386 days and pilots really have saved the A300 from bad conditions in the past. I still get the impression that some means to better integrate the pilots with the plane itself rather than via an automation condom might be worthwhile. Alas, nobody seems to agree on a way to do this which will not actually reduce the aircraft's reliability.
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Old 7th Jun 2011, 20:48
  #1573 (permalink)  
 
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Mach > 0.96
Has anyone ever done this in an airbus?
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Old 7th Jun 2011, 20:50
  #1574 (permalink)  
 
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a bit of altitude that is certainly felt. So I can only imagine the descent experienced by
AF44 would be felt quite a bit more. No?
It seems to me that it is entirely possible that as they were in the convection that caused the assumed pitot icing, that they would be subjected to a significant level of turbulance and so detecting the overall trend of the aircraft by feel could be unlikely.
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Old 7th Jun 2011, 20:59
  #1575 (permalink)  
 
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engineer-eer: is your point "PT2" a variation on the 5 measuring points of a gast turbine engine? IIRC, when we solved for various values in ideal engines, P1 = P2 was valid assumption, but doesn't that assume a few things about where one measures P2?

IIRC, IIRC, P1 is "outside" the system and P2 is "at the point of intake" and P3 is compressor discharge pressure P4 combustor out pressure and P5 exhaust pressure (afte it's been through the turbine wheels and made them spin) ... but it's been a few years since my turbojet engine class.

Something about using P2 to substitute for pitot air strikes me as very wrong, but I can't put my finger on it.

*My brain hurts, Mister Gumby!*
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Old 7th Jun 2011, 21:11
  #1576 (permalink)  
 
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Engine sensors.

@ engine-eer.

Wouldn't do it for GE.

P0 is static port on ECU.
Sensor in inlet is Temp sensor T12
PS1.2 is static pressure ports just IFO fan.
The only probe measuring dynamic pressure is P2.5 just after the booster, but this is only used for conditioning monitoring and that's an option.
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Old 7th Jun 2011, 21:13
  #1577 (permalink)  
 
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Originally Posted by A33Zab View Post
Went into the ADIRU today:
How and where? I was hoping somebody would have this sort of information.
Any links, or is this AMM or CMM type doc?
Makes lots of sense to this ancient.
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Old 7th Jun 2011, 21:17
  #1578 (permalink)  
 
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Thank you for the excellent post A33Zab

The PF slight but consistent nose up command is a +G request to the PRIMs, the A/C feedback by means of accelerometers however results in a -G.
PRIM deflects elevator and due to negative result drives the THS all the way ANU.
Is there a threshold of displacement for the sidestick before inputs are valid? How slight is slight? In the a/c I drive, stick neutral and elevator neutral are not the same thing. This lends the stick a "loose" feel in its neutral position. As CONF iture mentioned:

A particularity of the sidestick, depending how you grab it, is that it can be easy to involuntary command a NU or ND input by implying a generous side input.
Was that NU input intentional ...
PS: Can we infer the NU displacement from the info in the report:

The trimmable horizontal stabilizer (THS) passed from 3 to 13 degrees nose-up in about 1 minute and remained in the latter position until the end of the flight.
10 degrees in 1 minute. Are we talking about a displacement so small that, let alone the PNF, even the PF might not have noticed the input?
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Old 7th Jun 2011, 21:19
  #1579 (permalink)  
 
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mm43 - regarding feedback to the control stick I note that other forms of haptic feedback exist. I wonder if a vibration feedback to the pilot's back or some other convenient place could give a feel for control stick position without distracting the visual scan. If it was little vibrators in the seat back and one failed it would not be fatal such as an active stick force feedback might be. (Gus seems to hint that this can be done reliably enough military pilots will fly with it. But, as Dozy indicates it COULD be problematic if it went awry.)
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Old 7th Jun 2011, 21:30
  #1580 (permalink)  
 
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Originally posted by A33Zab ...

The PF slight but consistent nose up command is a +G request to the PRIMs, the A/C feedback by means of accelerometers however results in a -G.
PRIM deflects elevator and due to negative result drives the THS all the way ANU.

Unfortunate left unnoticed because any hand on the trim wheel had cancelled the PRIM THS orders.
A very enlightening post.

Manual inputs to the trim wheel override PRIM THS orders and the actuals are recalculated. That is how I understand it, and by implication, the PF could have braced himself using the trim wheel?
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