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A320 the big flaw of the UNRELIABLE SPEED/ADR CHECK procedure

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A320 the big flaw of the UNRELIABLE SPEED/ADR CHECK procedure

Old 15th Jun 2011, 01:43
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To MB2002

In regards to your first post about level off...
Standby ALT is what you need to look at...as I think was pointed out...the Static sensor runs straight to it without being "corrupted" by an ADR.
On take off the only reason why this sensor would be blocked would be if maintenance covered it up and it was not picked up on a walk round,...

To TyroPicard

1 which comes to mind was I think Lan Chile with exactly what happened above...the other methinks was an Air India....I will dig around and post if I find specifics..
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Old 15th Jun 2011, 02:02
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TP See Aeroperu 603

Still looking
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Old 15th Jun 2011, 05:45
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And speaking of A320 flaws, does anyone know why the NDs
default to a useless range of 80nm with a dual FCU fault? I've
never been able to find anything on the subject.

Given that ND info is still relevant at the time of the failures
and can be changed by FMC inputs, why isn't it defaulted to
a useful 40 or even 20nm?
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Old 15th Jun 2011, 08:02
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Code:
On a recent A320 sim-check, we had the following scenario :

In T/O just after rotation, we got 2 unreliable ADR`s, that both had the same failure of increasing airspeed, rapidly increasing to above 400 kts.

That means, that even though they are faulty, they wote out the remaining good ADR.

And what happens on the A320 in an overspeed situation : VMO/MMO + xx kts/0.xx mach, the A/C starts to pitch up, even though you manually try to pitch down !

And even more scary, with A/THR engaged, it reduce to idle due to higher speed than targetspeed. (We are not quite sure if this a "simulator thing" that it reduces to idle, can`t find anything about it in the books. Anyone confirm ??)

So with a rapidly increasing pitch and thrust at idle, things start to evolve very very quickly ! (and in this scenario very close to the ground). You have to do the following quickly, not a memory item (we are talking seconds) :

Solution : Select 2 ADR`s to off (doesn`t mean anything which two) and then you can apply the pitch/power procedure.

Question:

Once you have 2 ADR`S fault , you will be with :

AP , A/THR OFF
ALTN LAW (Protections Lost)

If the A/THR is off and you have protections lost , how come will the airplane start pitching up until you stall even with you above vmo?

Maybe I`m missing something..
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Old 15th Jun 2011, 08:28
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I am in the A330 fleet, the situation discussed here should be similar.

If an overspeed protection happening, no mater it is a true or false one, the protection function will trip off the AP and pull the aircraft up in 1.75 g for recovery and the pitch up command cannot be overriden by pilot's pitch down input. Until the disagree situation happens between ADR(s) and AOA(stall?), then automatic alternate law reversion happens and pilot's pitch down control can be achieved.

The question is if the aircraft went into deep stall before alternate law achieved, the recovery of the undesired aircraft attitude for the pilot could be a disaster. Refer to Airbus FCTM on Unreliable speed part, it mentions for extream case like we discuss here, switch off two ADRs will force the aircraft getting into alternate law right away, this may help to recover the unwanted overspeed and/or deep stall situation better.
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Old 15th Jun 2011, 18:33
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A3TWANTY

yes you are. The two "rogue" ADRs, which are equally wrong, reject the other one, which is correct. Democracy sometimes is bad

So you still have two "healthy" ADRs. there is no automation disconnection, no alternate law, nothing.... except a very dangerous situation
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Old 15th Jun 2011, 20:52
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Thanks Microburst,

Yes ,you are correct. They are not inop. It`s a disagreement of two which rejects the other one.

Last edited by A-3TWENTY; 15th Jun 2011 at 21:10.
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Old 16th Jun 2011, 10:01
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History

Tyro Picard # 40, the 3 cases mentioned by someone in a previous post.

Birgen Air, a B-757, captains pitot blocked. After take-off, as per SOP (for normal conditions), CTR autopilot was engaged.
CTR A/P uses left ADC, so the A/P reacted to the faulty IAS, pulled the aircraft into a stall and it crashed 10 nm north of POP, the departure airfield.

Aero Peru, static ports taped off, a/c came out of maintenance/washing.
Crew managed reasonably well for some time, then made the fatal mistake to regard "altitude information from ATC" as a reliable source (because it comes from "outside" the aircraft). Well, it isn't, because it is the pressure altitude as reported from your aircraft, using the transponder as transmission medium.
The reliable onboard source, independant from the pitot static system, in casu, the Radio Altimeter, was not believed, because at that stage, the crew did not believe any info from their aircraft anymore.

And number 3, you guessed correctly, will be AF447.
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Old 16th Jun 2011, 20:47
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When Did They Notice It?

Birgen Air, a B-757, captains pitot blocked.
Someone please correct me, but didn't they notice a difference between the captain's and the FO's airspeed indicators on take off roll but continued anyway?
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Old 16th Jun 2011, 23:59
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Originally Posted by Smilin_Ed
Someone please correct me, but didn't they notice a difference between the captain's and the FO's airspeed indicators on take off roll but continued anyway?
Yes, they did. The investigators' assertion was that having been away from home for several weeks while Birgenair tried to arrange a charter to get them home, the crew succumbed to "get-there-itis" and ignored a potentially dangerous discrepancy.

In fact the F/O's indicator was right all along, as was the standby - unfortunately the Captain assumed that because of the overspeed warning that the F/O's ASI was also incorrect, as it was showing a normal speed range (which in fact was correct). Boeing later retrofitted an Air Data Select switch to resolve the issue with the warnings and the autopilot.
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Old 17th Jun 2011, 06:38
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Boeing later retrofitted an Air Data Select switch to resolve the issue with the warnings and the autopilot.
That switch was standard on the 757/767 from the beginning. The Capt failed to reach forward and select ALT AIR DATA. Look at any 75/76 panel.

GB
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Old 17th Jun 2011, 09:52
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Originally Posted by Graybeard
That switch was standard on the 757/767 from the beginning. The Capt failed to reach forward and select ALT AIR DATA. Look at any 75/76 panel.
Are you sure?

The documentaries I've seen on the subject show a picture of the switch while stating that "Boeing changed their design to make it easier to select pitot data", or words to that effect.

I could be misinformed, but it's what I understood.
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