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?

It puts the jet into alternate law, therefore stopping the (erroneous) alpha protection.

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.

The OEB notes make mention that the affected aircraft was a 330 yet some 320 family aircraft have the same probes.

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.

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.

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.

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!

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?

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".

Because there are many other ways for non fbw aircraft to be flown into the ground as well?

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.

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... :}

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.

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!

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?

Sensors Not Probes
 

AOA are sensors not probes.
Pitots are probes not sensors.
AOA = capteurs
Pitots = sondes

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.

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!

Rsiano said:

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:

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: Is this what you are referring to?

probes, sensors, reversion modes, et al
 

Good frigin' grief.

Laws, modes, sensors, probes. Who gives a rodent ass?

I agree with Ber.

We can't bring back the cables or physical force feedback from the tubes and cables for most planes. Ultralights and many general aviation planes could easily get by and be safe and fun to fly. I relished my time in those planes, and we separated the wannabes from the folks with "touch" in short order most of the time.

I am an old fart but not one of those dinosaurs that are proud that they do not know anything about computers or such. When their system crashes on a desert island and don't know how many computers and servers and bandwidth stuff was involved so little Sally could use Facetime, they whine. So I flew the first really computerized attack jet, and then the next in line which was FBW. Big deal. I soon realized the limits of the near-artificial intelligence of the computers. I had to learn the inner workings because a) I depended on some of them to continue living, and b) I was a curious type. I also was in charge of the academics training for the first year and a half of F-16 training.

Our genesis pilots of the Atari generation in the F-16 in early 1980 was very revealing to we old farts. Our nuggets were admonished to remember what they had seen in "real" planes. You know, the ones that gave mechanical feedback( T-37) and the ones that had hydraulic control systems and feedback was just some dampers and springs ( T-38). A far cry from what I learned in the T-37 and T-33, with mechanical elevat.or and augmented roll

Ya know what? They done just fine. They exploited our avionics systems and appreciated the "protections" the FBW system provided, but they remembered basic aero and physics. They knew how to read a map and tune and interpret the VOR/TACAN/ILS and follow a paper letdown chart without a FMS. They were not "children of the magenta line". They used the cosmic avionics and such as the yutes do now with iPhones and such. They remembered how to fly and we never let them forget that.

The FBW and the cosmic avionics were there to help and not to rule.

If all we are now worried about is the definition of a probe or a sensor or whatever, then we are in dire straits. No difference whether the "sensor" went FUBAR or if the "probe" went to La La land.

The FBW systems must have a very clear reversion sequence and not have ten possible corrective actions, and then ten more once you have follwed rule 10,a,iii. GASP!!!

That's my story and I'm stickin' to it!

This AD does not mention icing per se. A blocked AOA probe does not necessarily mean it was iced up in icing conditions. One can refer to the Perpignan crash, as previously posted. The AOA probes 1 & 2 were blocked in clear weather, due to improper maintenance while washing the aircraft: a high pressure water jet was used to clean the fuselage, and water passed throught the first seal to lodge within the AOA probe's casings. Only after spending some time at altitude did the probes block up because the water inside the casings of AOA 1 & 2 had frozen up. Again, not ice accretion.

Due to the voting system logic, if two probes read "X" value and a third one reads "Y" value, the Y will be considered erroneous, regardless of the reality. There is no other way for the system to assess wrong ADR inputs/outputs.

This is where a pilot comes in handy. If you are lucky enough to get sufficient time to identify the failure before getting into a nose dive and and exceed VD, turning off two ADRs has a dual function: with only one ADR, the autoflight reverts to alternate, as previously mentioned, so speed protections are lost and the pilot will recover flight control authority, with the possibility of manually exceeding any high or low speed regime, as well as bank angles. That is just the way airplanes flew before FBW for the last 100 years almost. It's up to the pilot to keep the aircraft within the flight envelope.

The second function, is to force the system to use only one ADR source, thus removing any voting logic out of the equation. This should be a momentary solution, as the pilot , unknowingly, may have kept ON the ADR with a blocked AOA. Therefore, after full flight control authority has been recovered, investigating which of the ADRs has blocked AOA would be greatly beneficial, in order to get the SW working should other sh*te happen on the same flight. :ouch:

This is one of the reasons I have no time for pilots saying "We don't need to know the system in that much detail" or "I don't need to know that". We are not mere button pushers. Anyone not interested in aircraft systems should not be flying airplanes for a living. Imagine a soldier going to war, and doesn't care how his automatic rifle works, and says "nah, it's OK, you just need to pull the trigger, should work fine." See how far this soldier would go...

FLEXPWR, Willie Nelson
I will examine the situation again. When AoA sensors are stuck(for whatever reason) at low speed(higher AoA) position and the speed increases, when the alpha prot threshold is lowered the protection gest triggered. Will it go in dive and exceed limits? Not possible because alpha prot is a latching condition and will maintain that angle of attack which also is stuck at lower speed(higher AoA)value. The problem is not dive but involuntary/unwanted descent at alpha prot which cannot be reversed and can be critical close to ground. So by switching to alternate law you override the protection. On the PFD the actual speed will be correct but the display of Valph prot and V alpha strip will be erroneous since it is coming from AoA sensors in the wrong position. It is not possible to investigate which AoA sensor is faulty and you will have to fly in alternate law.The cockpit indication for unreliable air speed can confusing and there are many scenarios but not the one discussed above. However once diagnosed you will reject all of them fly by attitude ad thrust. This AD and OEB is intricate and meant for Airbus FBW operators so those who are not and holding PPL etc. should not read it and confuse themselves and definitely should refrain from forming any opinion about the aircraft.

Mutually Exclusive And Not Interchangeable Terms!
 

The pitot probe just captures air...the sensor is at the other end of the tube somewhere in the air data system.
The AOA sensor actually has the resolver built right in and is actually outputting a value to the computers.

not really new AD...
 

This airworthiness directive related to AOA is not really hot new in terms of issues. A33O and A340 had the same in 2012. (blocked AOA due to grease icing)


2 temporary revisions of airplanr flight manual were edited : TR 293 and TR 294 dec, 4th 2012, giving the same procedure as now published for A320.


Those temporary revisions can be found on EASA site.

Sorry, again I must poke my nose into a topic of which I have little experience, but it seems to me that amongst those that do (guys here that appear to be professional Airbus pilots, instructors and/or engineers) there is an awful lot of confusion and discussion. Surely if you guys do this for your living then there should be no discussion. A should equal A to every one of you, but instead it seems that each of you have different opinions of what this system means in the event of this sensor failing in this.mode. It does not give guys like me much comfort to know that (some) pilots might misunderstand their aircraft in certain situations.

As I said, bring back the cables.

Ber Nooly
A320 is a very easy aircraft to fly. Just like an ordinary calculator which any body can use but it is not easy to understand the logic and programme that goes into it. What is being discussed is not a normal operating procedure but pros and cons of a procedure in case of a very unusual situation. Unless you know something basic about A320 you should not get into this. At your stage you may have difficulty in understanding the cables of a 747 or MD11? To bring back cables you will have to get into a time machine because even the 737 is being made by Boeing under sheer pressure by customers like Southwest who wanted immediate equivalent of A320 neo.

Well said :D

Ber - if it puts your mind a little at rest, do NOT assume that all those claiming to be 'Airbus pilots' actually are. There are a lot of Walter Mittys around here.

vilas - "Unless you know something basic about A320 you should not get into this." The problem Ber and I see is that this seems to apply to a lot of the 'Airbus qualified' contributors too.

Way back I recall someone calling for a simple 'big red button' that can be pressed when HAL goes beserk, putting direct control back to the pilot with NO 'clever' software in the way so that the machine can be flown as an aeroplane while whatever has gone tits up is 'inverted'. Certainly having to start switching off bits of electronics while the machine tries to bunt you to your death does not come over as very reassuring to many. As flexpwr says
"This is where a pilot comes in handy. If you are lucky enough to get sufficient time to identify the failure before getting into a nose dive and and exceed VD, turning off two ADRs...."

As a former "Bus TRI, I don't see it a bad idea for these airplanes to have a "Direct Law" switch...the PRIM discrepancies on the (Qantas was it?) A330, and other incidents causing the airplane to deviate uncommanded from its desired flight path, would IMHO warrant this option to the pilots..AVIATE NAVIGATE COMMUNICATE and finally MANAGE...when the aircraft systems prevent one from the "aviate" bit, it sure makes things difficult

For those that want a "Direct Law/Alternate Law" reversion switch, it has one. Switching off 2 ADRs will have that very result. Its the quickest way of getting it into alternate law.

The other good one to have up your sleeve is the Emergency Electrical Config, to get in to that its 4 buttons.

The Airbus protections and computers can be switched off very quickly if required. Just be careful what you wish for.

yes..very easily done in inclement weather, never mind the startle factor, and possible confusion,(would everybody have thought of the ADR when their airplane pitched over into a dive and did not respond to sidestick inputs?) and bear in mind, that it's not only ADR issues that can cause problems, in any event, the DFDR and CVR will yield some interesting results

Being a Yank, and not one prone to believe that Big Brother is watching at every moment, I still wonder if we are getting the "Truth, the Whole Truth and nothing but the Truth."

This AOA probe issue is not new. There was a proposed AD from 2012 that suddenly was withdrawn. Makes you wonder.

https://www.federalregister.gov/arti...rbus-airplanes

The original AD was 2012-21-51. I think the EADS Lobby is very effective in Washington. They headed this AD off at the pass and it was never issued, until just last month. That's not surprising, we have the best Congress and Government money can buy.

jonty - by your own post "For those that want a "Direct Law/Alternate Law" reversion switch, it has TWO". (Or 4?) Which 2 to switch off? Which is the 'right' one?

In 'the old days', when the FMC or autopliot malfunctioned and you 'lost control', one click cured it. One click, near your thumb and not somewhere on a roof panel and you have an aeroplane back, and not a computer challenge.

What is the aversion amongst Airbus lovers to actually having control of the aeroplane? I do not understand it.

@Zaphod:
 

It was withdrawn because all conic plates should have been replaced by 'new' flat plates.

Apparently the conic plates, although suspected, were not the source of this issue after all.

Airbii crew are informed by FOT and there is sufficient explaining material on the Flight OPS section of 'Airbus World'.

Flagon and Jonty
The difference between pure FMS fitted conventional aircraft and FBW aircraft is mainly the protections soft in case of Boeing and hard in case of Airbus. These were basically designed so that pilot by his act cannot stall or over speed or overbank. But these parameters can get exceeded by environmental factors like angle of attack changing externally or over speed because change in wind and also by the AoA sensors or Pitot/static tubes getting fouled and triggering protections due to inappropriate data. These factors were not originally factored in the design of the aircraft so they have to come out with remedies. Immediate solution is through OEBs. I don't think airbus pilots will have objection to a switch to go into alternate law. It may come in future. Till then we follow manufacturers recommendations of switching two ADRs. EMER ELEC is not recommended so we simply don't do. EMER ELEC will knock out IR2 and IR3 after five minutes for rest of the flight and may have some other complications. Since these are not standard normal/abnormal procedures pilots discussing the event may appear divided or some may be partially incorrect but to take part in it or understand what is being said you need some knowledge of the flight control system.

vilas - "I don't think airbus pilots will have objection to a switch to go into alternate law." - my choice, if I were flying the machine, would be to DL and take the computers out of the circuit completely. We are, after all, talking about an emergency situation, so if crews were simply able to establish pitch and power for stable flight with NO interference/protections that would do me!

Not to sure about that one,
IFALPA objects to a direct AoA indicator, AF pilots objects the BUSS.....

A33Zab
As long as they don't object to the OEB they can't object to a switch which does the same job. BUSS is not used above 25000ft. and below that generally the problem is going to stay. Any way I don't think they will install a switch but they might modify the AoA sensor or the protection. They already have modified alpha prot protection during approach and landing after an accident.

Flagon
Now that you know why it happens it is not such an emergency. Alternate law has no danger. Direct law is a short term configuration to give you conventional aircraft response during landing. There is no feel and it cannot be practiced in aircraft. So not a good idea to suddenly get into.