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AF 447 Thread No. 6

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AF 447 Thread No. 6

Old 17th Aug 2011, 19:41
  #81 (permalink)  
 
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ISIS

STANDBY INSTRUMENTS D/O
ISIS
DESCRIPTION
The back of ISIS is equipped with two pressure connectors:
- one is connected to the standby pitot probe for total pressure
acquisition,
- the other one is connected to the combined standby static probes for
static pressure acquisition.
The ISIS indicator contains the following subassemblies:
- one pressure module,
- one inertial module,
- one computation module,
- one display module and,
- one interface module.
The pressure module is connected to the total and static pressure
connectors. Each pressure line is connected to a pressure sensor in
the pressure module. The inertial module is composed of three
gyrometers (gyrolaser) measuring angular speeds and two specific
linear accelerometers (pitch + roll). The computation module includes
a Central Processing Unit (CPU), which calculate the operational
parameters (attitude, altitude and airspeed), and a graphic card, which
receives the data from the CPU and sent it to the display module. The
display module is fitted on the front face of ISIS. It is of the Liquid
Crystal Display (LCD) type. The front face is also fitted with several
knobs for operation purposes. The interface module is composed of:
- a filtering board linked to an electrical connector at the back of ISIS,
- the 28V DC power supply unit,
- the interface board which links the pressure, inertial, computation
and display modules.
POWER SUPPLY
ISIS is supplied with 28V DC from the ESSential BUS bar. In case
of loss of this bus bar, the HOT BUS bar automatically takes over,
provided the Computed Air Speed (CAS) is greater than 50 kts. In
case of a power supply cut-off less than 50 ms, there is no effect on
the display.
OPERATION
When ISIS is energized, a delay of 90 seconds is necessary for
initialization. ISIS computes and displays own air and inertial
parameters. When the airspeed data is not valid, the CAS information
is provided as a back-up by Air Data/Inertial Reference Unit (ADIRU)
1 or ADIRU 3 regarding the ATT/HDG selector switch position. The
ADIRU also provides a Ground Speed (GS) information for
flight/ground condition, as a back-up. A BAROmetric selector knob
enables the display and adjustment of the standard barometric pressure
in hPa. When the Landing System P/BSW, located on the upper right
part of the indicator, is pushed, the G/S and LOC scales come into
view. The BUGS P/BSW allows to display the BUGS page. This page
is used to program characteristic speeds and altitudes displayed on
the related speed and altitude scales. The (-) P/B is used to get access
to the next bug and the (+) P/B to return to the previous bug. Air and
inertial parameters are processed by the computation module using
data from the pressure and inertial modules. The pressure module
sends the total and static pressure data while the inertial module sends
accelerations and angular rates data. Once computed, the parameters
are sent to the display module for indication to the crew. The LS data
is sent by the Multi-Mode Receiver (MMR) 1. Air Data/Inertial
Reference System (ADIRS) parameters computed by ISIS are sent to
the Flight Data Interface and Management Unit (FDIMU). The ISIS
can operate from 0 to 600 kts without deterioration of airspeed data.
It can operate from -2.500 to 55.000 ft and up to 40.000 ft/min without
deterioration of altimeter data. For the horizon data, the ISIS can

operate from -180 to +180 deg without deterioration.



A33Zab is offline  
Old 17th Aug 2011, 19:59
  #82 (permalink)  
 
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3hole

My issues are of design, and the use of trim in this case. The PF commanded a climb up without the assistance of TRIM. So either by good luck, or a/c design, the THS stayed put, and he relied on elevators only.

At the top, the design input TRIM after the STALL. That seems unwise. Commanded to be sure, but none the less, it responded.

Several of his inputs served to lower the NOSE, and the STALL sounded, and he pulled up again.

So, once STALLED, there would not only seem to be no need for all NU from the THS, but that it would be highly dangerous to leave it there.
With a continuous STALL warning, one would hope a 'smart' a/c would return the THS to neutral, and allow the Pilot to recover with elevators.

Since the speeds had returned, it becomes especially apparent (to the aircraft) full up THS is not a good thing? No alert, no lowering the THS,

I could easily be the thick one here, and not you.
Lyman is offline  
Old 17th Aug 2011, 20:07
  #83 (permalink)  
 
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BUSS

It would appear that AB sent a FOT saying that the BUSS system should not be used above F/L 25.0 on 9th. September 2009.
Because UAS above FL 250 is considered transient. (caused by ICE)

One need to switch all 3 ADR P/B to OFF to activate BUSS scale.



BUSS DESIGN
The BUSS is displayed on both PFDs. It is based on Angle Of Attack (AOA) information, and
enables to easily and safely fly the aircraft without any valid airspeed indication. The BUSS
enables to fly the aircraft in the entire flight domain while observing the design limits.
The BUSS scale is divided in three color-coded areas:
• In the green area, the aircraft has normal margin towards ultimate limits i.e. VMO/VFE for
upper limit and stall for lower limit
• In the upper and lower amber areas, the aircraft has limited margin towards ultimate limits.
Flying in the amber area is acceptable for a limited period of time but it should be avoided
• The red areas (FAST or SLOW) must be avoided.
The BUSS is tuned using the aircraft’s aerodynamic model with speed brakes retracted.
When the BUSS is active:
‐ The altitude indications are based on GPS data. Two amber dashes cover the last two
digits because the GPS altitude is less accurate than the barometric altitude
‐ The vertical speed indication is no longer available.
FLYING TECHNIQUE
The PF adjusts the pitch and thrust, to maintain the AOA in the green area of the speed
scale.
For approach, the flight crew should perform a stabilized approach. The flight crew should

change the aircraft configuration with wings level.






Last edited by A33Zab; 17th Aug 2011 at 20:22. Reason: Changed image
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Old 17th Aug 2011, 20:18
  #84 (permalink)  
 
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ISIS

A33Zab

Thank you for the details of the ISIS.

Could you add the size in inches (or mm) across the horizon, on the A/H part, so that I ( and others interested ) can adjust the scale on a monitor to be able to appreciate the instrument properly, as it might be viewed by a PF or PNF.
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Old 17th Aug 2011, 20:25
  #85 (permalink)  
 
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‐ The altitude indications are based on GPS data. Two amber dashes cover the last two digits because the GPS altitude is less accurate than the barometric altitude
‐ The vertical speed indication is no longer available.
Let me try to understand: static air data is deleted from the system? Is that what is going on in this mode?
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Old 17th Aug 2011, 20:38
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@LT:

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Old 17th Aug 2011, 21:10
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A33Zab,
Thanks for the pics and the info.
Was that the fit of the AF447 A330?
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Old 17th Aug 2011, 21:13
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So, once STALLED, there would not only seem to be no need for all NU from the THS, but that it would be highly dangerous to leave it there.
With a continuous STALL warning, one would hope a 'smart' a/c would return the THS to neutral, and allow the Pilot to recover with elevators.

Since the speeds had returned, it becomes especially apparent (to the aircraft) full up THS is not a good thing? No alert, no lowering the THS,
So, you're advocating more automation? I'm not disagreeing here... I actually think all the information required to help the crew was available.
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Old 17th Aug 2011, 21:15
  #89 (permalink)  
 
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@LW50:

All ADR data is removed when ADRs are switched OFF.

With this BUSS option installed the AOA signal is fed into IR part of ADIRU,
IR part is available even with Air Data P/B off.
Don't know if more inputs are re-routed.
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Old 17th Aug 2011, 21:31
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Lonewolf_50

3hole, a few threads back, I think number 4, a gent who has taught in the A330 simulator related to us how some Unusual Attitude drills and recoveries required use of the trim wheel, manually, to get the pitch under control (in other than normal law, IIRC) in a suitable time frame. He wasn't sure if that was a "simism" or not.

Point?

There were or are some training drills that can be used to accustomize crews to using the trim wheel to control nose pitch in cases where the auto trim is either too slow or not helping redirect the elevators and THS where the pilot needs them. You could call the trim wheels a secondary flight control (Not sure if I am right about that) which means any rated pilot ought to know, like the flaps, when and how to use it.

And practice doing so.
Is it anywhere referenced to use it in this situation? I could only find the following references, where the mechanical trim is desscribed as standby system in case of autotrim not being availble.


THS MECHANICAL CONTROL
The mechanical pitch trim commmands are achieved by the handwheels in the
cockpit and transmitted to the input shaft of the THS actuator.
The THS mechanical control can be used :
- on ground, to trim the stabilizer when electrical control is not possible.
- in flight, as a standby system if automatic control (autotrim) is not available. (REF. LTTM)
The control wheels are used in case of major failure (Direct
Law or mechanical back-up) and have priority over any
other command. (REF: FCTM)
The purpose of the mechanical backup is to achieve all safety objectives in
MMEL dispatch condition: To manage a temporary and total electrical loss, the temporary loss of five fly-by-wire computers, the loss of both elevators, or the total loss of ailerons and spoilers.
It must be noted that it is very unlikely the mechanical backup will be used, due to the fly-by-wire architecture. For example, in case of electrical emergency configuration, or an all-engine flameout, alternate law remains available. In the unlikely event of such a failure, mechanical backup enables the PF to safely stabilize the aircraft, using the rudder and manual pitch trim, while reconfiguring the systems. (REF. FCTM)
When automatic pitch trim is no longer available, the PFD indicates this with an amber USE MAN PITCH TRIM" message below the FMA. (Ref. FCTM)
THS MECHANICAL CONTROL
General
The Trimmable Horizontal Stabilizer (THS) has a mechanical control system.
You can use the mechanical control system on the ground to trim the stabilizer when electrical control is not possible. The mechanical control system is also used in flight as a standby system if automatic control is not available.
The mechanical control transmits mechanical pitch-trim signals, put into the
hand wheels in the cockpit, to the input shaft of the THS actuator. (REF. LTTM)
We know now that it might have helped to defuse the situation, how could the AF447 crew know? By not knowing the above references?
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Old 17th Aug 2011, 21:36
  #91 (permalink)  
 
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BUSS looks suspiciously like an AOA indexer.

I 'spect it's possible to have an indexer without shutting off the all the ADR's also.

We had an indexer in the training 727 we flew in the 80's, as well as a separate full-time AOA gauge.

Back to the future.
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Old 17th Aug 2011, 22:12
  #92 (permalink)  
 
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GY

Why wouldn't I be advocating for more automation? Or a better fit between what exists and the crew? Isn't that what this is all about?

If this airframe thinks enough of itself to protect the Rudder from inadvertent and harsh deflection, why would it not also want to protect itself from a TRIM trapped STALL?

If more than 8 degrees Rudder is not available at certain speeds, why would -13 PU be available? This is the "disconnect" I see from the outset of this thread, some logic here, some logic there, but something short of a continuous path in all directions.

It can be explained, but excuse me, pulling out the book and trying to get task specific recurrent in these conditions is insanity.

Knowledge plus experience equals wisdom. Substitute the word intuitive for wisdom, and there you go. Nothing that can occur on this aircraft can be permitted to be anything short of fluid, intuitive, and absolutely resistant to failure.

And that is the goal for when things are difficult, and doable; to say this argument is justifiable at all when problems of a familiar nature are involved is frankly outrageous.

It would be so nice to simply say PE. That is not any longer acceptable if one also expects to take credit for a failure resistant a/c when faults are so readily apparent?

We read here from guys who dream this stuff and live it. But there are real people here, and when some assume a posture of haughty self satisfaction that makes my fur hurt. The aircraft has holes, fill them.

all the best
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Old 17th Aug 2011, 22:39
  #93 (permalink)  
 
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A33ZAB,
Many thanks for the details of the ISIS.... looks and sounds very much like the SAARU in the triple 7. ...an everything-you-need-PFD-in-a-self-contained-box. Pop one of those in your little ragwing and you're home free!

Lyman.... Thanks for clarifying... One further comment, re: "If this airframe thinks enough of itself to protect the Rudder from inadvertent and harsh deflection, why would it not also want to protect itself from a TRIM trapped STALL?"
Because it is NOT "trapped" at all and there is no risk of structural damage as there is with the rudder.
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Old 17th Aug 2011, 22:56
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Originally Posted by CaptainGef View Post
Speed is decreasing and as speed is decreasing, they don't see it and what does the THS do on FBW machine?: It tries to maintain flight path, so as speed is decreasing to maintain flight path the autotrim goes up to the limit, incidence is growing up to maintain flight path.
On a Boeing, even in alternate law, you would have to trim as speed decrease to maintain flight path, it would alert you that something is wrong.
Autotrim will do exactly the same on a boeing if the automatics are trying to maintain a flight path (with speed decreasing). See Schipol 737 and similar accidents/incidents.

Not a FBW issue, not an AB issue.
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Old 17th Aug 2011, 23:17
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@3HL:

Many thanks for the details of the ISIS.... looks and sounds very much like the SAARU in the triple 7. ...
Minor correction:

-ISFD (Integrated Standby Flight Display) is the B. naming for ISIS.
-SAARU (Secondary Attitude Air data Reference Unit) is the "back-up" ADIRU of the777.

an everything-you-need-PFD-in-a-self-contained-box. Pop one of those in your little ragwing and you're home free!
Exact! 1 standby instrument for whole fleet! A. thru Z.
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Old 17th Aug 2011, 23:29
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@ChristiaanJ:

For ISIS, this ISIS was installed.
The BUSS option was NOT installed.
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Old 17th Aug 2011, 23:50
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3hl

"No risk of damage, as with the Rudder?" Methinks the reason the THS was not deployed in the climb, and the elevators were not allowed to grab too much at a time had to do with protections.

The a/c at the bottom is not Damage?

The Rudder could disintegrate and part the VS, no crash. The THS, at full NU does not risk damage to the a/c? What if they had recovered aero flight, and the THS remained at -13 in a steep and high speed dive. No risk of damage? What a ride. ?

No inference of applicability, but look at this. The Rudder on AA587 tore the VS off (That was at <250 knots). If 447 had been in a recovery from Stall, the THS couldn't take the Tail off? I wouldn't place a bet.
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Old 18th Aug 2011, 00:43
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OK465
BUSS looks suspiciously like an AOA indexer.
I concur, Increasing AOA is toward the bottom. Oriented this way to make the display read in a manner similar to airspeed. Note: There are no numbers on the display.

Shouldn't the note at the bottom right say:
Red lower area corresponding to CAS < VLS

AF447 would have been at the bottom of the bottom red band while on its way down. Even three highly confused aviators would have understood their plight then.
Well, lets hope so.
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Old 18th Aug 2011, 01:12
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Maybe the "whooler" shouldn't have been eliminated, but I'm not at all sure that would have made any difference here.
It might have though...

I think a THS position trim clacker might well have alerted PNF to something going very awry in pitch much earlier and at least have glanced at the wheel or pointed the Captain to it immediately upon cockpit re-entry ?

.. even if PF himself was 'focused down a very narrow tunnel of perception' and would likely have been aurally blocking it out.
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Old 18th Aug 2011, 01:19
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Originally Posted by infrequentflyer789 View Post
Originally Posted by CaptainGef
Speed is decreasing and as speed is decreasing, they don't see it and what does the THS do on FBW machine?: It tries to maintain flight path, so as speed is decreasing to maintain flight path the autotrim goes up to the limit, incidence is growing up to maintain flight path.

On a Boeing, even in alternate law, you would have to trim as speed decrease to maintain flight path, it would alert you that something is wrong.
Autotrim will do exactly the same on a boeing if the automatics are trying to maintain a flight path (with speed decreasing). See Schipol 737 and similar accidents/incidents.

Not a FBW issue, not an AB issue.
This is a drastic speed decrease, all the way down to a Stall condition, which is determined, and announced for 53 seconds by the "a/c's controls". Stall means fall !!!!

During these 53 seconds, of definite Stall Condition, determined by the a/c's computers, the THS went also under the a/c's computers control from -3 to -13 degree, which is MAX Nose Up, which is exactly the opposite of what in a Stall condition the pilot, or the computers should be commanding.

Personally, I would not consider this a FBW issue, in the sense of the FBW being a system in which the medium for transferring/passing bi-directionally control information is wire.

Is this really not an Issue??? if Boeing is doing to wrong thing, it is OK for AB to do the same?

Last edited by airtren; 18th Aug 2011 at 15:00.
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