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AF447

Old 14th Jun 2009, 20:37
  #1501 (permalink)  
 
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@graybard

MAINTENANCE WARNING REPORT
---------------------------
A/C ID DATE FLTN
XXXXX 090614 XXXXX
ECAM WARNING MESSAGE
+--------------+
GMT PH ATA SEQ DESCRIPTION
195X 06 27 90 400 F/CTL SENSOR FAULT

this is the normal format we get. To translate yr format

34 43/06
ATA chapter 34-43 flightphase 6
WRN WN0906010210
Warning Date 09.06.01 0210UTC
344300506 NAV TCAS FAULT
Failure code 344300 SEQUENCE 506 NAV TCAS FAULT
09-06-01 AF 447
IDENT


Normally no big deal .
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Old 14th Jun 2009, 20:37
  #1502 (permalink)  
 
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Originally Posted by barrymung View Post
As I understand it, the plane was fitted with three identical pitot tubes. Presumably, the reason 3 are fitted is in case one or more fails.

Who, in their right mind therefore, decided it was a good idea to fit three identical tubes, all from the same manufacturer, all of the same type and presumably the same date of manufacture??

If one tube had a stock fault, all three would have it.

Surely it'd be far more sensible to use three different tubes from three different manufacturers?

That way, if one failed, chances are the remaining two would be unaffected.
Well, there are various practical problems with dissimilar designs, especially for systems that need to have data in agreement from multiple sources in order to assure safe operation. With three different probe designs you'd get far more ADR DISAGREE type situations with the increased hazard that represents.

You also need to spec the dissimilar designs, and the performance specs would presumably be identical. Since the state of the art for pitot probe design is mature, chances are you'd get very similar designs even from dissimilar vendors.

You'd also end up with the same environmental spec, so the same conditions which would overwhelm one probe's heater capability (if that happens) might very well overwhelm all the dissimilar probes.

And, finally, they didn't put all their eggs in one basket. The ISIS/standby is using a different means in that the standard probes have ADMs at/near the probe, while the ISIS is (I understand) plumbed traditionally with the sensing as part of the ISIS unit. So if you were to have some kind of catastrophic design flaw that took out every ADM the ISIS should still be running.

I don't think the air data system designers are as clueless as you seem to think.
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Old 14th Jun 2009, 20:43
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If all Pitot tubes are essentially identical, why have airbus stated they need replacement?

There's either a slight difference in design or a problem with manufacture, which means that these new probes are (apparently) less likely to fail.

NASA take this approach of ensuring backup systems are all different, why not airbus?
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Old 14th Jun 2009, 20:44
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wheelie my boeing

In otherwords turbulence is incapable of moving the joystick despite it's significant moment arm and weight out on that moment arm?

I find that hard to believe.

{^_^}
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Old 14th Jun 2009, 20:45
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The aircraft needs two identical-ish engines for stable flight. The pitot tubes, however are somewhat different.
Really? I'll remember to bring my parachute next time I lose an engine on a twin since it can't possibly retain stable flight with one engine.
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Old 14th Jun 2009, 20:47
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And, finally, they didn't put all their eggs in one basket. The ISIS/standby is using a different means in that the standard probes have ADMs at/near the probe, while the ISIS is (I understand) plumbed traditionally with the sensing as part of the ISIS unit. So if you were to have some kind of catastrophic design flaw that took out every ADM the ISIS should still be running.
Well, something catastrophic obviously happened!
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Old 14th Jun 2009, 20:48
  #1507 (permalink)  
 
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@h3dubai:

Failure code 344300 SEQUENCE 506 NAV TCAS FAULT
does it mean "TCAS failure" or "TCAS power supply failure"??
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Old 14th Jun 2009, 20:50
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meekmok, you know what I mean!

Using your parachute analogy, you wouldn't jump out of a plane with a main chute and reserve which were both packed by the same guy, would you..?
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Old 14th Jun 2009, 20:51
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Originally Posted by barrymung View Post
Well, something catastrophic obviously happened!
Yes. "something" managed to apparently disable dissimilar systems.

Which implies that no dissimilar design philosophy can be foolproof.

All pitots stick out into the airflow. All are subject to icing, or to hail, or to birdstrike, etc. There is nothing you can do about that, except try to protect where you can. But you can't spec for icing massively outside the expected range, you can't build a pitot to be invulnerable to hail, and so on.

And AB aren't the only ones - indeed I'd say that it's normal for the primary air data systems to be of common design, with only (at most) a dissimilar standby system. That's what this a/c has.
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Old 14th Jun 2009, 20:56
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Originally Posted by barrymung View Post
If all Pitot tubes are essentially identical, why have airbus stated they need replacement?

There's either a slight difference in design or a problem with manufacture, which means that these new probes are (apparently) less likely to fail.
Not having read the SB or AD I don't know.

NASA take this approach of ensuring backup systems are all different, why not airbus?
The backup - ISIS - is dissimilar.

The multiply redundant systems are similar.

I think you'll find that's a common design approach. Including NASA-specced systems. (Who aren't exactly 'golden' when it comes to safety of design, so I wouldn't put them on a pedestal myself)
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Old 14th Jun 2009, 20:58
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does it mean "TCAS failure" or "TCAS power supply failure"??
it means TCAS FAULT , without the other faultcode , U can't specify.
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Old 14th Jun 2009, 21:00
  #1512 (permalink)  
 
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Originally Posted by barrymung
If all Pitot tubes are essentially identical, why have airbus stated they need replacement?

There's either a slight difference in design or a problem with manufacture, which means that these new probes are (apparently) less likely to fail.
Not having read the SB or AD I don't know.
Unless I misremember somebody has already established that the difference between the most recent update and its predecessor involved icing on the ground, not in the air. If so this is a dead horse issue.

{o.o}
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Old 14th Jun 2009, 21:08
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Old 14th Jun 2009, 21:15
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vs loss

After reading the facts about the JAL 123 flight when the a/c could fly for more than 30 min. after losing the VS everything is possible...
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Old 14th Jun 2009, 21:19
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photos of the wreckage

Check them out here:

Crash: Air France A332 over Atlantic on June 1st 2009, aircraft impacted ocean
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Old 14th Jun 2009, 21:24
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There is way too much blame being assigned here to a single entity be it a manufacturer or a single system.

The investigation is on-going and damn few facts are available to establish a causal chain. This thread is begining to look amateurish in its over simplification of what went wrong and who is to blame.

The idea that anybody involved with the investigation would not like to find the critical evidence (FDR/CVR etc.) is outlandish and demeans a supposedly professional internet site.

This is not about blame, lawyers or insurrance carriers, it's about finding enough information to prevent a similar accident.

Root cause is hogwash. Nobody can effectively eliminate any system malfunction whether it be pitot tube interactions with computers or a weather radar outage.

Our efforts need to be focused on minimization (of an occurrence) and mitigation (of the resulting hazard) To do this you need data on all the interactions that were at play in this accident including the pilots.

In today's machine you can not take the pilot out of the accident causal chain, yet nobody is even considering the what-ifs in this discussion. Remember for every system failure including the pilots there is a cause effect and that is ultimately how the corrective action will be accomodated.
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Old 14th Jun 2009, 21:30
  #1517 (permalink)  
 
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JD-EE

Back in the days of the first Jets control runs became more complex and at higher speeds their weight became too much for comfortable flying so servos were introduced. The problem with servos was that they did not always feed the control surface pressure back to the pilot so an artificial "feel" was added to control columns. IIRC it was called "Q Feel" and was considered rather revolutionary at the time.

Q Feel was necessary so pilots could judge, ( based on the old direct systems) how much their control surfaces were deflecting or pressing on the air and secondly, as the control pressure became significantly greater, would not deflect a control surface beyond what was safe.

Then true FBW came along. The control inputs are fed into a computer which judges the amount of control surface deflection required for the indicated manoeuver and applies it. The computer also ensures that the control surface is not deflected too much for the conditions so 'Q' is not necessarily required.

Now personally this worries me a bit, but, as someone pointed out on another thread where we were discussing this, the difference is not the risk of electric failure but the difference in risk between electric failure and physical component failure eg. cable or rod bearing etc., in systems which are both complex. There is little evidence so far in statistical terms that FBW is any less safe than the old physical connection controls.
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Old 14th Jun 2009, 21:31
  #1518 (permalink)  
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Originally Posted by JD-EE View Post
wheelie my boeing

In otherwords turbulence is incapable of moving the joystick despite it's significant moment arm and weight out on that moment arm?

I find that hard to believe.
Why?

Even your Microsoft Flight Sim pilot knows that early joysticks had no physical feedback. Only later games joysticks have feedback.

I don't know Airbus but there is no need for physical feedback. You place the joystick (computer mouse or whatever) in the direction you want it to go then you observe the effect. This may be an indication of control surface position, the movement an instrument etc. The feedback is visual and not physical.
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Old 14th Jun 2009, 21:35
  #1519 (permalink)  
 
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Assuming, that no VHF coverage is avail. ACARS is communicating via SATCOM. To contact the satellite, the A/C has to know his position in regard to the satellite to adjsut the dish.
ACARS is linked with most of the computers , so it should be easy to track it by sending LAT/LON datas.
I believe it's been established there is no dish. They use Inmarsat as their carrier. And the antenna is omnidirectional for this mode.
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Old 14th Jun 2009, 21:41
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Wheelie

Who is talking about feedback?

In severe turbulence, sufficient to damage a plane, is the pilot's seating secure enough that the transient accelerations of the plane are not going to move the pilots arm out of the pilot's control in response to the accelerations?

Will a stick with no hand on it stay perfectly still poking up there in the air above the mounting point as the plane accelerates with rapid jerks in random directions?

This is independent of whether the stick's output is controlling the plane or not. It's a question about whether under very heavy turbulence the input to the stick from the effects of the turbulence is stable enough to fly the plane. If not and the pilot HAS control isn't it possible that the bouncing around could lead to improper or damaging imputs to the flight control system?
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