PPRuNe Forums

Go Back   PPRuNe Forums > Flight Deck Forums > Tech Log
Forgotten your Username/Password?

Tech Log The very best in practical technical discussion on the web


Reply
 
Thread Tools Search this Thread
Old 25th Dec 2012, 08:35   #1 (permalink)
 
Join Date: Feb 2011
Location: China
Age: 33
Posts: 10
A320 OEB Blocked AOA probes

An Airbus aircraft encountered an all Angle Of Attack (AOA) probes
blockage during climb. With the Mach number increasing, the blockage
led to Autopilot (AP) disconnection and activation of the alpha
protection.
PROCEDURE:
CAUTION Monitor the Alpha Prot strip and the Alpha max strip when they are visible
At any time, if the aircraft goes to an unmanageable pitch down attitude despite
continuous deflection of the sidestick in the full backward position (in case the flight
crew missed the below symptoms or delayed the application of one of the below
procedures):
ONE ADR......................................................... .......................................................KEEP ON
TWO ADRs........................................................ ............................................................ ...OFF In stabilized flight path (out of maneuvers involving an increase in load factor such as
turns or pitch variations), if the Alpha Max strip (red) is visible and hides completely
the Alpha Prot strip (black and amber):
SPEED / MACH........................................................ ............................... DO NOT INCREASE
 When at or above safety altitude:
LEVEL OFF......................................................... ..................................................INITIATE
Limit speed and altitude in order to limit the Mach number and to prevent the activation
of Alpha Prot, even if the Alpha Prot strip is not displayed on the PFD.
ONE ADR......................................................... ..........................................................KE EP ON
TWO ADRs........................................................ ............................................................ ..... OFF
The AP, FDs and ATHR are lost for the remainder of the flight.
Switch two ADRs to OFF for the remainder of the flight in order to revert to alternate law to
prevent undue Alpha Prot activation.
In case of dispatch with one ADR inoperative, switch only one ADR to OFF.
FPV USE......................................................... ........................................................CONS IDER
SPEED / MACH / ALTITUDE.................................................... ...............DO NOT INCREASE
 With AP ON, and with speed brakes retracted if, during maneuvers involving an
increase in load factor such as turns or pitch variations, the Alpha Prot strip (black
and amber) moves rapidly by more than 30 kt :
SPEED / MACH........................................................ ............................... DO NOT INCREASE
 When at or above safety altitude:
LEVEL OFF......................................................... ..................................................INITIATE
Limit speed and altitude in order to limit the Mach number and to prevent the activation
of Alpha Prot, even if the Alpha Prot strip is not displayed on the PFD.
ONE ADR......................................................... ..........................................................KE EP ON
TWO ADRs........................................................ ............................................................ ..... OFF
The AP, FDs and ATHR are lost for the remainder of the flight.
Switch two ADRs to OFF for the remainder of the flight in order to revert to alternate law to
prevent undue Alpha Prot activation.
In case of dispatch with one ADR inoperative, switch only one ADR to OFF.
FPV USE......................................................... ........................................................CONS IDER
SPEED / MACH / ALTITUDE.................................................... ...............DO NOT INCREASE
 After setting the flaps lever to 0, if the ECAM displays "A LOCK" and "A LOCK"
remains displayed when the aircraft speed is at VFE CONF 1:
SPEED....................................................... ......................... MAINTAIN BELOW VFE CONF 1
Maintain the speed below VFE CONF 1 in order to prevent the OVERSPEED warning from
triggering at VFE CONF 1 + 4 kt.
The VFE CONF 1 strip is not displayed when the flap lever is set to 0.
FLAPS LEVER....................................................... .......................................................CONF 1
SPEED SEL......................................................... ...................................................... S SPEED
 When at or above safety altitude:
LEVEL OFF......................................................... ..................................................INITIATE
Limit speed and altitude in order to limit the Mach number and to prevent the activation
of Alpha Prot, even if the Alpha Prot strip is not displayed on the PFD.
ONE ADR......................................................... ..........................................................KE EP ON
TWO ADRs........................................................ ............................................................ ..... OFF
The AP, FDs and ATHR are lost for the remainder of the flight.
Switch two ADRs to OFF for the remainder of the flight in order to revert to alternate law to
prevent undue Alpha Prot activation.
In case of dispatch with one ADR inoperative, switch only one ADR to OFF.
FPV USE......................................................... ........................................................CONS IDER
SPEED / MACH / ALTITUDE.................................................... ...............DO NOT INCREASE



i have a question, why we do this action one ADR on and the other two keep off,what is the meaning of doing this?
pacinolove is offline   Reply
Old 25th Dec 2012, 09:26   #2 (permalink)
 
Join Date: Jan 2001
Location: Around the world.
Age: 34
Posts: 577
It puts the jet into alternate law, therefore stopping the (erroneous) alpha protection.
tom775257 is offline   Reply
Old 25th Dec 2012, 10:37   #3 (permalink)
 
Join Date: Apr 2005
Location: Stockholm Sweden
Age: 65
Posts: 550
Quote:
Angle Of Attack (AOA) probes
blockage
Is this a modified probe of some sort?
All the A320/330 I have ever worked on have the airfoil type AOA probes which fly in the wind, not the type with holes in that can get blocked.

Airbus AOA probes can freeze, but cannot get blocked.
Swedish Steve is offline   Reply
Old 26th Dec 2012, 08:11   #4 (permalink)
 
Join Date: Oct 2007
Location: Iriomote
Posts: 183
The OEB notes make mention that the affected aircraft was a 330 yet some 320 family aircraft have the same probes.
TwoTone-7 is offline   Reply
Old 26th Dec 2012, 09:40   #5 (permalink)
 
Join Date: Oct 2009
Location: UK
Posts: 1,273
Hi TwoTone-7,

There are about 170 A330s fitted with these conic AOAs and over 500 A320s.

The A330 mentioned had the new "conic" plate AOAs fitted, but freezing problems have occurred previously with the old design. This example jammed at a cruise angle of attack. See:Sensor icing caught out A320 crew in Perpignan crash

Edit. with thanks to CONF iture.
If Pitots and AOAs simultaneously iced up then -
The pitch / power tables will resolve which is telling lies, but I don't think HAL can read those tables.

Last edited by rudderrudderrat; 27th Dec 2012 at 08:07. Reason: Missing conditional sentence
rudderrudderrat is offline   Reply
Old 26th Dec 2012, 10:25   #6 (permalink)
 
Join Date: Mar 2009
Location: pre-dep area
Posts: 164
Actually, the probes themselves were not changed, but were equipped with conic plates that protect the probes.

It is these conic plates that have the "probe holes" in them.
capt. solipsist is offline   Reply
Old 26th Dec 2012, 21:16   #7 (permalink)
 
Join Date: Jan 2005
Location: W of 30W
Posts: 1,848
Quote:
Originally Posted by rudderrudderrat
The pitch / power tables will resolve which is telling lies, but I don't think HAL can read those tables.
Actually, except from consulting the Aircraft Computer Maintenance System, it is not possible for the crew to compare the different AoA readings.
It is good to remind that all pitch displays are correct and also all IAS. Only the presented limit speeds are incorrect.

But the challenge is really on taking back the aircraft control that the duped protection thought necessary to grab.
CONF iture is offline   Reply
Old 5th Jan 2015, 13:36   #8 (permalink)
 
Join Date: Jan 2007
Location: I wish I knew
Posts: 753
If the aircraft pitches down and Alpha Floor activates, it'll be through Mno in no time. What happens then? Does the FBW give up and resort to Alternate Law? I guess simultaneous Alpha Floor and Mmo, with an all red speed tape could be quite disorientating!
ZeBedie is offline   Reply
Old 5th Jan 2015, 14:50   #9 (permalink)
 
Join Date: Jan 2008
Location: Doylestown, Pennsylvania
Age: 77
Posts: 55
Ground the aircraft!

Considering the effect that this computer makes it impossible for the pilot to over ride the nose down means to me to never climb on board an Airbus aircraft. Why do the authorities permit an aircraft with this characteristic to fly?
rsiano is offline   Reply
Old 5th Jan 2015, 16:15   #10 (permalink)
 
Join Date: Jun 2007
Location: Malaysia
Posts: 984
Frozen/blocked Pitot/static and frozen AoA probes are two different situations. In frozen Pitot case one ADR is kept for stall warning which comes from AoA probe and not for pressure data like speed, altitude etc. When AoA probes are frozen at lower speed and aircraft accelerates to higher cruise/Mach the alpha prot threshold decrease to appx. 5degrees of AoA while the system is getting higher frozen value and that can trigger Alpha prot protection based on this erroneous data. So the only way to get out of the hard protection of normal law is to get into alternate law by switching two ADRs off. The third is kept to give you speed but if Pitots are also blocked that will also be incorrect. This AD is not very comprehensive and doesn't cover both frozen Pitot and Pitot together can mislead the pilot if Pitots are also blocked. A320s which have MOI153528/P12909 the FPV is modified to calculate FPA from hybrid GPIRS(mixed IRS and GPS position). So you can use it in this case. But without this MOD bird can only be used provided Pitot/static is not blocked and that is why the wording "FPV consider".
vilas is offline   Reply
Old 5th Jan 2015, 16:42   #11 (permalink)
 
Join Date: Aug 2007
Location: no longer 110m overhead
Age: 54
Posts: 2,282
Quote:
Originally Posted by rsiano View Post
Considering the effect that this computer makes it impossible for the pilot to over ride the nose down means to me to never climb on board an Airbus aircraft. Why do the authorities permit an aircraft with this characteristic to fly?
Because there are many other ways for non fbw aircraft to be flown into the ground as well?
glad rag is offline   Reply
Old 5th Jan 2015, 18:05   #12 (permalink)
 
Join Date: Mar 2005
Location: between the clouds
Posts: 95
With regards to switching off 2 ADRs, does it matter which 2 we switch off?

From what I understand, when this failure occurs, the computer has already rejected 1 ADR. Or does the computer revert back to the only ADR it has available although it rejected the ADR earlier.

The difference between All ADR off and ADR 1+2 (dual failure), should be quite significant.
cav-not-ok is offline   Reply
Old 5th Jan 2015, 18:27   #13 (permalink)
 
Join Date: Apr 2013
Location: everywhere
Posts: 107
I don't think it matters, but it's good to leave the one operating on PF's side - found it the hard way in the sim...
C_Star is offline   Reply
Old 5th Jan 2015, 18:28   #14 (permalink)
 
Join Date: Jun 2007
Location: Malaysia
Posts: 984
cav-not-ok
What is the situation? In case of icing of Pitots if you switch of ADR2 FO looses his speed, with ADR1 Capt. looses speed. ADR3 is loss of standby. But it doesn't matter if all are faulty. With AoA blocked speeds are valid and you need it so PF should switch off the other two. What computer rejects will depend. It is a voting system so two similar reading ADRS will reject the third disagreeing ADR. But that is not always correct because in case of two faulty but similar reading ADRs the lonely correct ADR will be rejected. With all triple ADR failure or double ADR failure CAS/Mach disagree if second is not self identified you get alternate law without protections. With double ADR failure alpha disagree you get alternate law with reduced protections.

Last edited by vilas; 5th Jan 2015 at 19:04.
vilas is offline   Reply
Old 5th Jan 2015, 19:37   #15 (permalink)
 
Join Date: Oct 2001
Location: EIR15
Posts: 47
As a PPL I have a headache from just reading all this.

It seems such an unnecessarily complicated set of procedures to follow in the very infrequent event that you will need to. It seems too complicated for a human brain to follow in a moment of heightened anxiety. Unnecessarily so. A computer could do it, but not a human. Too much room for error when it's not a task that is practiced repeatedly.

Bring back the cables and vacuum gauges, I say!
Ber Nooly is offline   Reply
Old 5th Jan 2015, 20:09   #16 (permalink)
 
Join Date: Jan 2007
Location: I wish I knew
Posts: 753
Can I ask again, please. When the aircraft accelerates through Mmo, due to blocked AOA with pitots working normally, what happens to the flight control laws? Alternate law (salvation) or nothing?
ZeBedie is offline   Reply
Old 5th Jan 2015, 20:17   #17 (permalink)
 
Join Date: Oct 2013
Location: Wengen
Age: 45
Posts: 256
Sensors Not Probes

AOA are sensors not probes.
Pitots are probes not sensors.
AOA = capteurs
Pitots = sondes
Winnerhofer is offline   Reply
Old 5th Jan 2015, 20:23   #18 (permalink)
 
Join Date: May 2000
Location: Glorious West Sussex
Posts: 998
Calm down everyone...well, some of you...
This is not an instantaneous malfunction requiring superhuman ability and lightning reactions. If the probes are blocked then Alpha Prot strip will rise progressively towards the climb speed as you climb, giving you plenty of warning. The obvious solution at this point is to descend if circumstances allow, land and write up the maintenance log.
Regarding which ADRs to turn off.. in the absence of an ECAM ADR caution it does not matter.. If you turn off 1+2 you can transfer 3 to either pilot which may be an advantage. Either that or 2+3 so the Captain has valid airspeed.
TyroPicard is offline   Reply
Old 5th Jan 2015, 20:35   #19 (permalink)
 
Join Date: Oct 2013
Location: Wengen
Age: 45
Posts: 256
BR Incident: AOA Gold Standard

Why no mention of BR incident December 2012?
https://www.youtube.com/watch?v=nw-0ZYHoEWw
Get this man a drink!
Winnerhofer is offline   Reply
Old 5th Jan 2015, 22:13   #20 (permalink)
 
Join Date: Feb 2002
Location: Australia
Posts: 232
Rsiano said:

Quote:
Considering the effect that this computer makes it impossible for the pilot to over ride the nose down means to me to never climb on board an Airbus aircraft. Why do the authorities permit an aircraft with this characteristic to fly?
Really? This is a misunderstanding of the system, the entire point of the OEB is to provide pilots with a specific means by which to avoid the highly unlikely scenario that has occurred less times a Kim Kardashian wedding.

I suspect many if not most experienced Airbus pilots would have been able to get the aircraft in to alternate law if push came to shove but this clears up all ambiguity.

Personally, I would take control as PIC and have the FO switch off the two ADR's closest to him. (3 and 2) however Airbus doesn't care which one, it just states that it has to be done within 15 seconds. Now people as far as what is essentially a recall goes, this is as easy as it gets.

Vilas said:

Quote:
This AD is not very comprehensive and doesn't cover both frozen Pitot and Pitot together can mislead the pilot if Pitots are also blocked
Perhaps I have misunderstood what you are trying to say. If you had the jammed, stuck or frozen AOA devices at the same time as a frozen pitot or pitot/static system (if that's what you meant) surely you would apply OEB 48 first and then apply unreliable airspeed.

As you yourself said vilas:
Quote:
Frozen/blocked Pitot/static and frozen AoA probes are two different situations
Is this what you are referring to?
Willie Nelson is offline   Reply
Reply
 
 
 




Thread Tools Search this Thread
Search this Thread:

Advanced Search


Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT. The time now is 23:31.


vBulletin® v3.8.7, Copyright ©2000-2015, vBulletin Solutions, Inc.
SEO by vBSEO 3.6.1
1996-2012 The Professional Pilots Rumour Network