A330/A340 EAD (AoA PROBES)
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“...sometimes used to ponder, during my walk-rounds, on the pros and cons of locating Pitots 1 & 2 at precisely symmetrically-opposite positions on the fuselage (Pitot 3 being the odd one out). Then I would remind myself that the same applied to the AoA probes. It seemed to me that this might be a recipe for (roughly) simultaneous ice accretion of numbers 1 & 2."
Symmetrical position of AoA vanes is very common, the longitudinal position of A33/A34 is much further aft (aft of pax door#1) than e.g. the T7 (just below the flightdeck aft window).
Airbus don't want the surrounding skin to be heattreated so the base of the AoA sensor lacks a heating element this in contradiction to the T7.
....did the AoA sensors really iced up?
An A330 aeroplane, equipped with Angle of Attack (AoA) sensors with conic plates installed, recently experienced blockage of all sensors during climb, leading to autopilot disconnection and activation of the alpha protection (Alpha Prot) when Mach number was increased.
Based on the results of the subsequent analysis, it is suspected that these conic plates may have contributed to the event. Investigations are on-going to determine what caused the blockage of these AoA sensors.
Blockage of two or three AoA sensors at the same angle may cause the Alpha Prot of the normal law to activate. Under normal flight conditions (in normal law), if the Alpha Prot activates and Mach number increases, the flight control laws order a pitch down of the aeroplane that the flight crew may not be able to counteract with a side stick deflection, even in the full backward position.
This condition, if not corrected, could result in reduced control of the aeroplane.
condition on Airbus A330 and A340 aeroplanes.
AoA conic plates of similar design are also installed on A320 family aeroplanes, and installation of these AoA sensor conic plates was required by EASA AD 2012-0236, making reference to Airbus SB A320-34-1521 for in-service modification. This requirement has now been removed with revision 1 of that AD.
To address this condition on A320 family aeroplanes, Airbus developed an “AOA Blocked” emergency procedure, published as a temporary revision (TR) of the Airplane Flight Manual (AFM), to ensure that flight crews, in case of AoA sensors blockage, apply the applicable emergency procedure.
For the reasons described above, this Emergency AD requires insertion into the AFM of the Airbus TR.
This AD is considered to be an interim measure and further AD action may follow.
Based on the results of the subsequent analysis, it is suspected that these conic plates may have contributed to the event. Investigations are on-going to determine what caused the blockage of these AoA sensors.
Blockage of two or three AoA sensors at the same angle may cause the Alpha Prot of the normal law to activate. Under normal flight conditions (in normal law), if the Alpha Prot activates and Mach number increases, the flight control laws order a pitch down of the aeroplane that the flight crew may not be able to counteract with a side stick deflection, even in the full backward position.
This condition, if not corrected, could result in reduced control of the aeroplane.
condition on Airbus A330 and A340 aeroplanes.
AoA conic plates of similar design are also installed on A320 family aeroplanes, and installation of these AoA sensor conic plates was required by EASA AD 2012-0236, making reference to Airbus SB A320-34-1521 for in-service modification. This requirement has now been removed with revision 1 of that AD.
To address this condition on A320 family aeroplanes, Airbus developed an “AOA Blocked” emergency procedure, published as a temporary revision (TR) of the Airplane Flight Manual (AFM), to ensure that flight crews, in case of AoA sensors blockage, apply the applicable emergency procedure.
For the reasons described above, this Emergency AD requires insertion into the AFM of the Airbus TR.
This AD is considered to be an interim measure and further AD action may follow.
They removed the requirement of installing conical plates but NOT TO REMOVE the conical plates from factory delivered and in service modified aeroplanes.
Question: Will a max. 4° elevator down - due to activation of Hi AoA protect - command a 12° pitch ND?
Or will the Anti Pitch Up Compensation - blended in from M 0.65 to max 6° elevator down - had more effect on the 12° pitch down?
(New procedure states: DO NOT INCREASE SPEED !!)
@CONF: I have to say it again……..sometimes manual pitch trim can be your best friend!
Last edited by A33Zab; 7th Jan 2013 at 16:53.
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A33Zab...
Yes, symmetrical positioning of redundant sensors is common. 'Commonplace' and 'traditional' does not mean such positioning is not arbitrary.
Positioning sensors such that their relative ability to sense is dependent on common condition is not necessarily rational.
It merely makes them susceptible to failure when the ambient condition is unexpected
Why is it always ICE?
In the current condition, the symmetry is flawed....
Predicting (and making dependent) any multiple system on the 'expected' is
not sound.....
At the bottom of all this is the utter lack of a simple test for failure....
"Let's fail AoA, and see the response..."
"Let's fail Airspeeds, and assess autotrim..."
"Let's allow the ASI to drop to zero, and Test STALL WARN..."
"Let's put some knackered crew in the sim, and stuff the A/P...."
"Let's study manual handling in divergent Law/axis..."
What have I missed?
Oh... Isn't THS busy in this case, workin' ND ? Does the new AFM include, "Without Delay"?
Yes, symmetrical positioning of redundant sensors is common. 'Commonplace' and 'traditional' does not mean such positioning is not arbitrary.
Positioning sensors such that their relative ability to sense is dependent on common condition is not necessarily rational.
It merely makes them susceptible to failure when the ambient condition is unexpected
Why is it always ICE?
In the current condition, the symmetry is flawed....
Predicting (and making dependent) any multiple system on the 'expected' is
not sound.....
At the bottom of all this is the utter lack of a simple test for failure....
"Let's fail AoA, and see the response..."
"Let's fail Airspeeds, and assess autotrim..."
"Let's allow the ASI to drop to zero, and Test STALL WARN..."
"Let's put some knackered crew in the sim, and stuff the A/P...."
"Let's study manual handling in divergent Law/axis..."
What have I missed?
Oh... Isn't THS busy in this case, workin' ND ? Does the new AFM include, "Without Delay"?
Last edited by Lyman; 7th Jan 2013 at 18:43.
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@CONF: I have to say it again……..sometimes manual pitch trim can be your best friend!
Now if you think you can counter a protection with the use of the trim wheel, you have all my respect and I'd better call you Chuck Yeager.
Nevertheless note that the Airbus AFM Temporary Revision has still no mention of the manual pitch trim to counter the elevators ...
Reading between your lines, do I detect a whiff of doubt that the AoA blockage was ice of any kind/origin?
Re the recovery: just a few initial thoughts, with hindsight from my comfy armchair.
It will be interesting to see if the crew used “speedbrakes” (airbrakes), and I wonder if they would have any effect on pitch trim on the A330. (If they were splitable, like on some a/c, you could use only the outers to generate pitch-up.)
Did we agree on the AF447 thread that manual THS is physically possible in Normal Law? Some early jets like the B707 provided (yes!) automatic stabiliser-trim (up) at high Mach,to counter the nose-down effect of Mach “tuck”. So perhaps it might not be such a challenge as you are suggesting, Conf_iture?
The cure must be to reduce Mach by going down and (at least) not allowing the TAS to increase. The latter doesn’t necessitate a reduction in IAS. Selection of idle thrust aggravates the trim, malheureusement, but if the THS is available that effect can be countered. Meanwhile, in case one hasn’t enough to do already, should one consider turning out of the “airway”, as per an emergency descent?
Re the recovery: just a few initial thoughts, with hindsight from my comfy armchair.
It will be interesting to see if the crew used “speedbrakes” (airbrakes), and I wonder if they would have any effect on pitch trim on the A330. (If they were splitable, like on some a/c, you could use only the outers to generate pitch-up.)
Did we agree on the AF447 thread that manual THS is physically possible in Normal Law? Some early jets like the B707 provided (yes!) automatic stabiliser-trim (up) at high Mach,to counter the nose-down effect of Mach “tuck”. So perhaps it might not be such a challenge as you are suggesting, Conf_iture?
The cure must be to reduce Mach by going down and (at least) not allowing the TAS to increase. The latter doesn’t necessitate a reduction in IAS. Selection of idle thrust aggravates the trim, malheureusement, but if the THS is available that effect can be countered. Meanwhile, in case one hasn’t enough to do already, should one consider turning out of the “airway”, as per an emergency descent?
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It was not ICE that crumpled 038 into a ball. At the worst, it was contributory. The problem was a mechanical deficiency (sic) that was modded/remedied in a device not intended to de ice, the FUEL OIL HEAT EXCHANGER. That is the story, and some one is sticking to it.
The 320 is not at risk. It is included in the AD for safety and or red herring' sake. Placement of probes? Possibly, but that means probes are not the problem either, at least potentially.
Simultaneous failure of probes, pitots, Statics.
Three day old fish. Thales is having a rough patch.
The 320 is not at risk. It is included in the AD for safety and or red herring' sake. Placement of probes? Possibly, but that means probes are not the problem either, at least potentially.
Simultaneous failure of probes, pitots, Statics.
Three day old fish. Thales is having a rough patch.
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Originally Posted by Chris Scott
Some early jets like the B707 provided (yes!) automatic stabiliser-trim (up) at high Mach,to counter the nose-down effect of Mach “tuck”. So perhaps it might not be such a challenge as you are suggesting.
To me the use of the trim wheel to counter the unjustified activation of a protection is much more than a challenge, it is pure Experiment.
I believe that if it was the preferable solution, it would be the one mentioned in the Airbus AFM Temporary Revision.
I'm not a big fan of the double ADR OFF selection either but it is IMO a piece of cake compared to what A33Zab is suggesting.
Without any hesitation my recommendation, for what it worth, would be to install a very accessible switch to both pilots to simply cancel any undue activation of a protection.
It would be for sure a Tsunami in regards of the ideological concept as advertised by BZ, but on the technical side it would be nothing.
Am I asking for the unreasonable ... ?
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Totally agree, the AFM TR should be followed!
But alleged 'total loss of pitch control' is besides the truth.
Learmount link
But alleged 'total loss of pitch control' is besides the truth.
Learmount link
The ability to remember, however complex our digital aeroplanes have become, that in the end they are still just aeroplanes, is a priceless asset for pilots.
The following event would have been confusing but, as ever, a couple of cool heads, some systems knowledge, and an ability to revert to basics can save the day. Here goes:
"Since the European Aviation Safety Agency issued an emergency airworthiness directive requiring airlines prepare their Airbus A330 and A340 pilots to cope with the effects of stuck angle of attack vanes, more detail has emerged about the nature of the event that sparked the new measures.
"As the A330 was climbing through FL113 (11,300ft) at about 250kt indicated airspeed, with the outside air temperature at minus 12C, the angle of attack vanes became stuck at an indication of 5°.
"Airbus says it is keeping its mind open as to whether this was icing-related or some other fault, but icing appears likely because the unit, manufactured by Goodrich, became unstuck during the descent.
The pilots had no direct indication of the stuck vanes and continued to climb toward cruise altitude. But at FL310, as the Mach number increased, the effect of the stuck vanes showed itself through the activation of the "alpha prot" stall-protection system, which pitched the nose down.
"Effectively, the combination of high Mach number and a falsely-indicated 5° angle of attack misled the A330's flight-control system into concluding the aircraft was approaching a high-altitude stall, so it took automatic action to reduce the angle of attack.
"At all times during the flight, says Airbus, the indicated airspeed was reading correctly, but the stall-protection system depends on angle-of-attack readings.
"The crew levelled the aircraft and turned off all three air data reference (ADR) units. This action took the aircraft out of normal flight law into alternate, which de-activated the stall-protection system. Then the pilots reviewed the situation and decided to divert. During descent, Airbus notes, the angle-of-attack vanes became unstuck once more.
"When the event occurred Airbus notified its customers, via an all operators telex, as well as EASA, under the mandatory occurrence reporting system. But there has been no call for a formal incident investigation.
"After consultation with Airbus, EASA issued an emergency airworthiness directive requiring airlines to amend A330 and A340 flight manuals to include a drill for pilots to adopt if this situation occurs. This drill largely reflects the actions of the incident crew: level out, taking account of safety altitude, maintain the same airspeed, then trip out two of the three ADUs to achieve alternate flight control law, which disengages the angle-of-attack protection.
"Airbus has praised the pilots of the A330, commenting that their systems knowledge and airmanship was good. During the remainder of the flight to the diversion airport, which was uneventful, Airbus noted that they kept a close eye on their attitude, power and airspeed relationship, because neither the artificial horizon nor the airspeed indicator was affected by the angle-of-attack sensor problem.
"Airbus says this is the only know occurrence of this type, but it is reviewing the design of its heated sensors and their resistance to icing.
The following event would have been confusing but, as ever, a couple of cool heads, some systems knowledge, and an ability to revert to basics can save the day. Here goes:
"Since the European Aviation Safety Agency issued an emergency airworthiness directive requiring airlines prepare their Airbus A330 and A340 pilots to cope with the effects of stuck angle of attack vanes, more detail has emerged about the nature of the event that sparked the new measures.
"As the A330 was climbing through FL113 (11,300ft) at about 250kt indicated airspeed, with the outside air temperature at minus 12C, the angle of attack vanes became stuck at an indication of 5°.
"Airbus says it is keeping its mind open as to whether this was icing-related or some other fault, but icing appears likely because the unit, manufactured by Goodrich, became unstuck during the descent.
The pilots had no direct indication of the stuck vanes and continued to climb toward cruise altitude. But at FL310, as the Mach number increased, the effect of the stuck vanes showed itself through the activation of the "alpha prot" stall-protection system, which pitched the nose down.
"Effectively, the combination of high Mach number and a falsely-indicated 5° angle of attack misled the A330's flight-control system into concluding the aircraft was approaching a high-altitude stall, so it took automatic action to reduce the angle of attack.
"At all times during the flight, says Airbus, the indicated airspeed was reading correctly, but the stall-protection system depends on angle-of-attack readings.
"The crew levelled the aircraft and turned off all three air data reference (ADR) units. This action took the aircraft out of normal flight law into alternate, which de-activated the stall-protection system. Then the pilots reviewed the situation and decided to divert. During descent, Airbus notes, the angle-of-attack vanes became unstuck once more.
"When the event occurred Airbus notified its customers, via an all operators telex, as well as EASA, under the mandatory occurrence reporting system. But there has been no call for a formal incident investigation.
"After consultation with Airbus, EASA issued an emergency airworthiness directive requiring airlines to amend A330 and A340 flight manuals to include a drill for pilots to adopt if this situation occurs. This drill largely reflects the actions of the incident crew: level out, taking account of safety altitude, maintain the same airspeed, then trip out two of the three ADUs to achieve alternate flight control law, which disengages the angle-of-attack protection.
"Airbus has praised the pilots of the A330, commenting that their systems knowledge and airmanship was good. During the remainder of the flight to the diversion airport, which was uneventful, Airbus noted that they kept a close eye on their attitude, power and airspeed relationship, because neither the artificial horizon nor the airspeed indicator was affected by the angle-of-attack sensor problem.
"Airbus says this is the only know occurrence of this type, but it is reviewing the design of its heated sensors and their resistance to icing.
A33Zab,
Thanks for quoting David Learmount’s piece from a month ago. The rest of us have been a bit slack in missing it, and I didn’t even know he had a website.
Looks like freezing of trapped water again?
Conf_iture,
For what it’s worth, my comments on splitting the spoilers (part of the jammed-stab drill on the B707, but I don’t think it’s possible on Airbus FBW aircraft) and use of THS in opposition to FBW-originating down-elevator were mainly to illustrate the severity of the problem facing this crew, and the lack of options other than that of finding a way out of Normal Law (without making the situation worse). They seem to have done a good job.
Thanks for quoting David Learmount’s piece from a month ago. The rest of us have been a bit slack in missing it, and I didn’t even know he had a website.
Looks like freezing of trapped water again?
Conf_iture,
For what it’s worth, my comments on splitting the spoilers (part of the jammed-stab drill on the B707, but I don’t think it’s possible on Airbus FBW aircraft) and use of THS in opposition to FBW-originating down-elevator were mainly to illustrate the severity of the problem facing this crew, and the lack of options other than that of finding a way out of Normal Law (without making the situation worse). They seem to have done a good job.
Last edited by Chris Scott; 8th Jan 2013 at 17:47. Reason: Restoring lost text
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As remote as it may sound, with simultaneity comes the occasional surprise.
Conical Plates? I would first look to reject something peculiar to altitude, such as minute deformation of the pressure vessel. At 11.5, the pressure altitude has been reached, and passed, the skin is starting to flex independently of the outside pressure.
Odds? 10,000/1. Worse?
If loss of two ADR creates Alternate, and BUSS takes it to DIRECT, should (can) BUSS be deselected? Or preferred?
Conical Plates? I would first look to reject something peculiar to altitude, such as minute deformation of the pressure vessel. At 11.5, the pressure altitude has been reached, and passed, the skin is starting to flex independently of the outside pressure.
Odds? 10,000/1. Worse?
If loss of two ADR creates Alternate, and BUSS takes it to DIRECT, should (can) BUSS be deselected? Or preferred?
Last edited by Lyman; 8th Jan 2013 at 18:51.
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@Lyman:
If loss of two ADR creates Alternate, and BUSS takes it to DIRECT, should (can) BUSS be deselected? Or preferred?
BUSS can be deselected by restoring 1 ADR, don't know if the Hi speed protection is also restored.
Odds? 10,000/1. Worse?
Last edited by A33Zab; 8th Jan 2013 at 19:28.
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Protection must protect
CONF iture:
A dangerous mechanism of protection must be "fired" when required.
The process of change is a complex one.
A dangerous mechanism of protection must be "fired" when required.
Am I asking for the unreasonable ... ?
It would be for sure a Tsunami in regards of the ideological concept as advertised by BZ, but on the technical side it would be nothing.
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Totally agree, the AFM TR should be followed!
But alleged 'total loss of pitch control' is besides the truth.
But alleged 'total loss of pitch control' is besides the truth.
The A320 memory items from the OEB (my bold):
At any time, if the aircraft goes to an unmanageble pitch down attitude despite continuous deflection of the sidestick in the full backward position (in case the flightcrew missed the below symptoms or delayed the application of one of the below procedures):
One ADR........Keep on
Two ADR's......Turn off
One ADR........Keep on
Two ADR's......Turn off
If you are too late, alpha prot will engage and you will loose all control over pitch which can only be resolved by the memory items.
The A330 crew lost all control, but they regained it by turning ALL adr's off which forced alternate law.
Last edited by 737Jock; 8th Jan 2013 at 22:05.
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Pursuing the academic point, does alpha-prot have authority to drive the elevator to its AND limit?
From the ATSB (interim) report on QF72:
From the ATSB (interim) report on QF72:
The aircraft manufacturer advised that the 10-degree elevator command associated with the first in-flight upset, was the result of 4 degrees of alpha prot and the 6 degree authority of the anti pitch-up compensation. The 10-degree command was close to the worst possible scenario that could arise from the design limitation in the AOA processing algorithm.
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I'm intrigued by the mention of an "ideological concept", and I'd love to know what it is...
Last edited by DozyWannabe; 9th Jan 2013 at 22:33.
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Originally Posted by DOZY
I'm intrigued by the mention of an "ideological concept", and I'd love to know what it is...
But Never was mentioned that pilots could be necessary to protect the airplane from FCS that would make mistakes as well.
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And to allow pilots to command manoeuvres up to the physical limits of the flight envelope without worrying about falling out of the sky, but that doesn't get brought up as often.
It might not have been heavily publicised, but the procedures enabling a pilot to do so have been in the flight manual for as long as the aircraft has been around.
But Never was mentioned that pilots could be necessary to protect the airplane from FCS that would make mistakes as well.
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It might not have been heavily publicised, but the procedures enabling a pilot to do so have been in the flight manual for as long as the aircraft has been around.
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Originally Posted by DOZY
It might not have been heavily publicised, but the procedures enabling a pilot to do so have been in the flight manual for as long as the aircraft has been around.
Why didn't they simply remind to all the reference of that procedure as it is already part of their flight manual ?
To kill the protections should be done through a single switch, easily accessible to both crew members.
To have to switch 2 ADRs OFF on the overhead panel in order to "prevent the flight control laws from using two coherent but unreliable ADR data" is a **** procedure when your airplane started to behave on its own against any logic.
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But when manual trim is used to counter alpha prot, you get the full AND value
Please explain to me why manual trim to full AND is required to counter alpha prot - in this case - when they wanted the nose to go up.
