B777 Procedure Blocked AOA Probes

[Kimon]

In the light of the BR A333 incident, what are the procedures regarding blocked AOA probes on the B77W?

[maui]

Same as any aeroplane. Power + Attitude!!!

[5LY]

Pitch and thrust as Maui says. You should have a basic target pitch and thrust target setting in your head for all realms of flight. They don't have to be precise. If you're in the ball park, you can quite easily keep the blue side up while you find the unreliable airspeed checklist which will take you to a landing. There are many eicas checks that pop up which are mostly a waste of time. Do them, but focus on pitch and thrust.

I ran many of these in the sim in IMC. With a bit of briefing with respect to pitch and thrust targets, I never had anyone fail to land safely.

[777fly]

To be completely accurate, the AoA sensors of the AF 330 never iced up, it was the pitot probes. In my experience of the B777 in identical conditions, it is the engine P1 sensors that ice first. The autothrottle disengages and thrust ref indications disappear, but the A/P stays in. You have time to look up attitude and thrust settings in case the worse happens, but the pitot probes stay clear for 10 minutes or more. As everyone advises, maintain thrust level and attitude and wait to fly clear, its rarely more than a few minutes to do that.

[CONF iture]

But the question by Kimon is different :
What's happening on a 777 if the AOA probes block at the same angle ?
Is there a possibility for one protection to take over and for the airplane to ignore the pilot's inputs like it did happen on a 330 ?
BTW how many AOA probes on the 777 ?

[AlphaZuluRomeo]

To be completely accurate, the AoA sensors of the AF 330 never iced up, it was the pitot probes.
Ahem... I think you're remembering another dramatic event, there.
What is the topic looks more like related to this (http://www.pprune.org/rumours-news/502079-a330-a340-ead-aoa-probes.html). ;)

[777fly]

AZR: Thank you for the correction. Should have read the OP more carefully....

[Kimon]

Yes, more on that BR (EVA) A333 underreported incident:

« ILS » n (http://www.asso-af447.fr/Technique-aeronautique/l-ils-r-nont-pas-retenu-la-lecon-de-laf447.html)

Les dossiers noirs du transport aérien (http://henrimarnetcornus.20minutes-blogs.fr/)

[spannersatcx]

BTW how many AOA probes on the 777 ?0..........

[CONF iture]

Photos: Boeing 777-3B5/ER Aircraft Pictures | Airliners.net (http://www.airliners.net/photo/Korean-Air/Boeing-777-3B5-ER/1943995/&sid=f9b77879d44c3eccb5cf72c41b8a2a65)

To me, it looks like one in that red circle ... ?
And apparently another one on the left hand side, for a total of two ?

[A33Zab]

What's happening on a 777 if the AOA probes block at the same angle ?
Is there a possibility for one protection to take over and for the airplane to ignore the pilot's inputs like it did happen on a 330

Continued activation of the stickshakers & increased column force in the nose up direction.
Don't know the effect on the Flight control computers.

...A330 pilots SS input is not 'ignored', a further nose up input will not be possible if AoA [when blocked] ~ AoAmax.
Roll control will not be affected and SS ND input (if situation permits) will cancel the hi alpha protection
.....but if AoA vanes are still blocked it will reactivate the hi alpha protection on each SS NU input.

BTW how many AOA probes on the 777 ?

2 is correct! and like the Airbus of the vane type.

[CONF iture]

SS ND input (if situation permits) will cancel the hi alpha protection
To the contrary, SS ND inputs will get the airplane deeper into the high AoA protection ... and closer to the VMO/MMO too ...

When a pilot cannot counteract the pitch down ordered by a protection, by pulling the sidestick in the full backward position, I think it is fair to state that his SS inputs are 'ignored'.

[A33Zab]

To the contrary, SS ND inputs will get the airplane deeper into the high AoA protection

FCOM 1.27.20 P 4

To leave the angle-of-attack protection :

The sidestick must be pushed more than 8° forward, or
The sidestick must be pushed more than 0° forward, for at least 1 second, when α < α max, or
α < α prot, if the sidestick has not been deflected since the latest autopilot disconnection.

[spannersatcx]

They are sensors not probes, probes work in a very different way to AoA sensors.

It may be pedantic, but there is a very big difference between the 2 and how they work.

So there are 2 AoA sensors, but 0 AoA probes.

[Kimon]

Good point!
So to recap for clarity's sake:
Pitots are probes.
AOA vanes are sensors.
Static ports are probes?Sensors?
Have static ports ever known to fail?

[spannersatcx]

Have static ports ever known to fail?

in a way, after hangar maintenance or washing tape has been left covering them before, not really a failure of the static port in itself.

In some modern a/c the tubing that was once many many feet long is now very short and goes to an electronic sensor, these can fail, but not that often. Most common failures are the heater parts of probes.

[CONF iture]

FCOM 1.27.20 P 4
But we're not in the FCOM register here, when everything works by the book, malfunctions included.
We are in the Wild Territory of the Airbus World, where the unexpected was not planned.

Don't forget : Some AoA probes are telling the same lie to the boss ...

[Kimon]

The B777's ADIRU has 6 accelerometers with superior skewed axis combinations and redundancy.
When Pitots fail, any set of 3 sensors will define a solution vector in 3-space.
It follows that 6 non-parallel sensors result in 20-solution vectors.
If there are no errors, the solutions will all be the same within accuracy limits of the system.
If there is 1 faulty sensor,10 of the solution vectors become "wrong".
If a 2nd sensor fails, it also affects ten vectors but 4 are included in the first 10.
That means 2 failures results in 16 "wrong" out of twenty solutions.
The task of identifying the 4 "right" is done!

[A33Zab]

A failed sensor is something different then sensing identical but - wrong - information.

In case of a failed sensor the FW bit is set and this enables a system to respond to it, as you described.

But the T7 will sense the same -wrong- information, like the EVA A330 did, because the 3rd comparable value is the average of both sensors.
3 identical AoA is accepted as GOOD information.

[Kimon]

Many thanks, A33Zab!
Given that the brains and voting system are the same whether B777 or A330, the rub is how the architecture of the aforementioned aircraft subsequently handle failures of Pitots, AOA sensors and StatPorts.
Yes, granted horses for courses within a game of two halves but is the B777 overrall back-up and breakdown systems of SAARUs and simplified degraded Modes simply better?
Obviously you can not have a B system in an A and vice-versa.
http://www.coe.pku.edu.cn/tpic/20119263710178.pdf

[CONF iture]

But the T7 will sense the same -wrong- information, like the EVA A330 did, because the 3rd comparable value is the average of both sensors.
3 identical AoA is accepted as GOOD information.
But the T7 will not kidnap the control as the 330 does.

[A33Zab]

AoA protect is there for a reason, don't have to explain you that, unfortunally it was activated when not appropriate, fortunately there was and is a solution to overcome.

Question: what will be the instinctive reaction of the PF when stickshakers are suddenly activated?

Both JTSB as ASC did not initiated an investigation, although you say the control was 'kidnapped',
nobody - on this forum -seems to be concerned about that one.........shouldn't we?

@Kimon:

I admit the dual ADIRUs/SAARUs concept in B will be more robust against multiple failures compared to the 3 ADIRUs concept of A.
In single failure and in case of similar but - wrong data - it will not make any difference.

FWIW:

In A350 airbus will supply the ISIS (optionally a repeater for RH seat) with its dedicated pitot and static ports.
The triple ADIRUs concept will remain however with dedicated multifunctional probes (MFP) and slideslip sensors.
Only ADIRU#1 will be equipped with an additional normal AoA sensor.

[CONF iture]

Question: what will be the instinctive reaction of the PF when stickshakers are suddenly activated?
Hopefully an initial push ... until, still hopefully, things point to the undue stickshaker activation and therefore the possibility to stabilize the situation, possibility refused to an Airbus crew before he shut a few computers down.

Some serious questions need to be asked why investigation bodies do not investigate a loss of control leading the EASA to publish an EMERGENCY AIRWORTHINESS DIRECTIVE and Airbus to modify its Flight Manual ...

That the event was "unfortunate" seems good enough for you to keep it quiet ... I just don't follow you on that path.

[A33Zab]

Hopefully an initial push ... until, still hopefully, things point to the undue stickshaker activation and therefore the possibility to stabilize the situation, possibility refused to an Airbus crew before he shut a few computers down.


Just like the A330 did, but they have to overcome the increased force to stabilize and keep the continuing stickshackers.
most probably they will (ICW OCC!) continue in Direct and silence the shackers with CB. also dual - non procedural - action required.


Some serious questions need to be asked why investigation bodies do not investigate a loss of control leading the EASA to publish an EMERGENCY AIRWORTHINESS DIRECTIVE and Airbus to modify its Flight Manual ...

That the event was "unfortunate" seems good enough for you to keep it quiet ... I just don't follow you on that path.

On the contrary...I do agree! it is serious matter and should be investigated.
The only 'excuse' I can imagine is that the source of this INCIDENT was that obvious (mechanical blockage) they left it to EVA QA - as first in line - to investigate.
In the EAD it is not mandated to remove the conical plates or replace the AoA sensors in factory delivered airbii.

[gums]

Yes, Kimon, the static ports have been known to freeze up.

No big deal until you climb or descend, and then altimeter doesn't change but the CAS/IAS does. With all the stuff we now have and a knowledge of power and pitch for various flight conditions you're usually in good shape.

Having the AoA sensors freeze at identical angles could be tricky, as you might lose some "protections" at higher true AoA.

Several here have experienced static system problems and are still here to contribute.

[CONF iture]

Just like the A330 did, but they have to overcome the increased force to stabilize and keep the continuing stickshackers.

777 - It is possible to override the unjustified protection.
330 - It is NOT.


The only 'excuse' I can imagine is that the source of this INCIDENT was that obvious (mechanical blockage) they left it to EVA QA - as first in line - to investigate.
In the EAD it is not mandated to remove the conical plates or replace the AoA sensors in factory delivered airbii.
By focusing on the conical plates, you're missing the bigger picture : How a Flight Control System is giving FULL priority to an unjustified protection and how a crew is needed to save the aircraft that was supposed to save the crew ...

[DozyWannabe]

If people think the T7 won't behave strangely or contrary to pilot command if given duff data, have a look at this article (h/t Clandestino - my bold):

What happened on flight MH124 - Nation | The Star Online (http://thestar.com.my/news/story.asp?file=/2005/9/20/nation/12084071&sec=nation)

According to the report by the Australian Transport Safety Bureau released on its website last Friday, the pilots were alerted to a low airspeed warning at an altitude of 11,582m.

At the same time, the primary flight display indicated that the plane was turning left, while the speed display showed that the plane was “going too fast and too slow simultaneously”.

The plane then pitched up to 12,497m and the indicated airspeed decreased from 500km/h to 292km/h.

At this point, the stall warning and stick shaker devices were activated.

...

The report revealed that Capt Norhisham then disconnected the autopilot and lowered the plane’s nose to prevent the stall.

However, the aircraft’s automatic throttle, which should have been off, came on again and compensated by increasing speed.

Capt Norhisham countered this by pushing the thrust levers to the idle position but the aircraft pitched up again and climbed another 610m.

EDIT - Clarification: Clandestino mentioned the incident, not the article itself.

[CONF iture]

If people think the T7 won't behave strangely or contrary to pilot command if given duff data

Strangely YES
Contrary to pilot command NO


Show me the data of the elevator down when the pilot commands it up ... ?

[DozyWannabe]

Show me the data of the elevator down when the pilot commands it up ... ?

Not sure what you're referencing here - but you know the T7 system doesn't work that way, instead it will gradually increase PFC resistance to the pilot's input via the backdrive system.

In the case of Airbus Alpha prot (as you well know), elevator down in response to a nose-up command is to maintain the aircraft at the alpha prot AoA, because to follow the pilot's command directly would result in an imminent stall.

[A33Zab]

Quote:
Originally Posted by A33Zab
Just like the A330 did, but they have to overcome the increased force to stabilize and keep the continuing stickshackers.


777 - It is possible to override the unjustified protection.
330 - It is NOT.


IMO in A330 it is also 'overridable'.......manual pitch trim (to level off), I know....it's not in the procedures.

[Kimon]

Are the following statements true on the B777 if it were an AF447?

1) Turning off the ADRs so as to force it in Secondary Mode à la A330 Alternate 1?


No. You can't turn the ADRs off in flight on a 777. The only way I know to force Secondary Mode is to open the pitot probe heat circuit breakers (which a normal flight crew should NEVER do).


2) B777 is w/o aural SW only yokeshakers so it is not subject to the 60KNS / 30 KNS cut-out set-up?


I *think* (but am not positive) that the shaker would cutout when the airspeed when too low, for the same reasons that the Airbus aural cuts out.


3) B777's equivalent of THS AutoTrim is that trims for speed only not pitch.


Not exactly. The 777 uses elevator for fast commands then trims the stabilizer to offload the elevator. 'Trim" on a 777 is really an aerodynamic state that's a combination of current elevator and stab positions, not an explicit state of either one individually.


4) Pitch authority is always driven via the elevators that command the stabs as opposed to the A330's separate - "divorced" - authority i.e. THS AutoTrim is separate entity that does not rely on elevator authority at all?



Both systems rely on both. AutoTrim and 777 stab trim are both composite systems that work together with the elevators to give the pilots what they ask for with minimum drag. The 777 has speed stability as part of the control law but, depending on the flight regime, the actual pitch command trying to return the airplane to trim speed might be elevator, stab, or both.

[CONF iture]

IMO in A330 it is also 'overridable'.......manual pitch trim (to level off), I know....it's not in the procedures.
then time for a new PFD message :
MANUAL PITCH TRIM ONLY TO FIGHT ELEV

but I love your optimism ...

[A33Zab]

Thx..:hmm:

Normal USE MANUAL PITCH TRIM will do!

[CONF iture]

MAN PITCH TRIM ONLY + USE IT NOW !
In the wait for the single guarded switch ... I will also stick with the ADRs.