Re; “ Why must we assume that it was ice that did provoque an unreliable Airpseed situation ”

Supporting Blacksheep’s answer (#73, #79), see the presentation Instrument External Probes.
For ref, the certification Appx C for icing is on page 126 of CS 25 Large Aircraft, also see Fig 5 (page 182) and compare the events (outside the cert envelope) with the information on The Ice Particle Threat to Engines in Flight and other similar references to engine problems which involved TAT anomalies.

The relevance of TAT freezing is as an indicator of the ambient conditions (temp/ice/water near large Cbs), also that the displayed temperature will always change (increasing temp).
Whereas with pitot icing the indications may not change unless altitude is changed (trapped pressure) or there could be fluctuating indications as shown in the first link. Thus there could have been many more pitot icing events which went unnoticed – and involve a range of aircraft types depending on the type of pitot probe and how the data is ‘managed’ before being displayed.

Also see The Ice Crystal Weather Threat to Engines slides 7 & 19 - TAT anomalies & Appx C.

safetypee - ice crystals..
 

well aware of the ice crystal - engine compressor icing debate..

would like to throw the following into the debate..

the weather has not changed that much in the last 50 years..

let's assume the atmospheric conditions described in these phenomena have been around for a long while..

Question: Could it be that we all are too cozy with all the new technology nowadays and fly closer to storms more often than in earlier times..???!!!

falconer1 – “…we all are too cozy with all the new technology nowadays and fly closer to storms more often than in earlier times…”

Absolutely, Yes !
Investigations of several of the engine incidents (pre 2000) indicated that the fight crews, who had moved up from commuter / older aircraft, were using the ‘new’ digital radars without appropriate conversion training. Thus they flew in the ‘green areas’ closer to storm centres than they would have done previously.
Other crews, brought up on the new equipment showed some complacency. Avoiding a clearly defined storm edge on the WXR could be finessed; crews did not question if they had generated the picture correctly, nor that some storms are much more severe than others – ‘they forgot to be afraid’ (James Reason).
More recently the trend is reversing with the focus on turbulence, but even this is challenged with the economics of operation and airspace constraints.
IMHO crews lack deep knowledge of systems operation and limitations, particularly in relationship to the threat of weather – we all lack time for additional learning, and suffer to some extent from commercial pressure.

The atmosphere hasn’t change, except that perhaps we are flying higher and thus experiencing a different set of conditions (a little bit colder, a little thinner air, ‘just small changes’, etc).
Also, other aspects of technology have changed. Many of the ‘supercritical’ technologies have been applied to engine components and possibly probes; modern systems use smaller, fine tolerance parts, which proportionately might suffer ice (or other particle) contamination more readily. They may require higher standards of maintenance.

Like many aspects of safety, hazards originate from change, particularly when we don’t notice the changes.
What is disappointing in this accident is that it appears that many of the probe problems were known and the hazard severity identified even by the regulator, but the safety activities were not applied proportionately or in time.
No blame, just seeking an understanding from which we might learn.

agree - safetypee, BUT
 

lest somebody thinks I get carried away with a very subjective view of the subject ( aren't we all??) let's not forget for our statistics guys...

we also fly A LOT MORE.. more planes more flights..

and all in all we are tons safer now..

maybe just a lot more critical if something happens..

so let's stay real..

a lot of superb guys & gals out there flying superb airplanes..

with a safety record, nobody would have believed possible a couple of decades ago...

It's A Man Machine Interface Issue
 

More and more our accident causal chains are containing man and machine interface issues.

We have less and less all machine or all crew issues as the primary cause (in spite of some folks that use probable cause in reports)

Yes the overall accident rate is decreasing since the paper I presented in 1992 but we still have a lot to learn about to how to live with the systems that we create.

As always we need to not only identify the causal factors but decide as an industry where and how to address those that are most common today

Do we improve the machine or the man since neither will achieve perfection?

Man machine Interface
 

Lomapaseo
Now you're talking. We will continue to improve the machines...but the interface to a human is THE critical component in the total performance picture.
I had this discussion with Al Smith at MDC years ago (around the time of the DC-9-50). The man/machine interface has to be intuitive!! And, here is the crux, it has to be intuitive to the pilot...not the engineer who designed it!!
When I was at Bendix, the RDR 1E and 1F Pilot's Guides were written by engineers. Most pilots didn't read them.
I rode a lot of jumpseat with CO, WA, FR, MX. AW, HA, AN, AV, and Air Mic, talking with crew about the use of WXR. A colleague did the same with other airlines. We agreed that most pilots are non technical!! WXR is also subjective. That drove the development of color and Doppler, both attempts to make the radar less subjective. It's better but not perfect.
I have always been concerned with the automation in the aircraft failing and handing the aircraft off to the pilot at the worst possible moment. Not sure how we prevent that scenario, but if I were flying the airplane I'd want to have some hands on, in a sim or benign conditions, practice, to prepare for that contingency. I think that training is most important.

Actually I recall reading a study that was trying to quantify why the size of super-cooled water droplets was increasing. Speculation was that it was due to several things, one of them being the decrease in particulate matter in the atmosphere due to lower levels of certain types of pollution. The end result from our perspective was that the icing models that had been used to certify a/c deicing systems were no longer valid and would have to be reevaluated. A link to the study when I can locate it again.

Or didn't understand what they meant.

Yes indeed, the line rides were good for both sides. The trouble is we don't always think with the same side of our brains, but we have to get over this hurdle!!

It's good to knock heads even if it's only in forum words with guys like PJ2 and Safety Pee etc. etc. We're going to get there if only because we care.:ok:

OT
 

I must know you, Putt, and you can't be Stan Lipnicki. I knew Al Smith at DAC also.

The avionics manufacturers wrote Pilots' Guides, and few of them reached the pilots. They were too expensive to just hand out, after all. Besides, how many pilots would have read them?

Today, it's so easy to put a PG on a site, with unlimited access.

I did get to provide limited pilot training during re-currents. One Capt. said, "Don't use it in Wx; it attracts lightning." I was caught flatfooted by that, but recovered, saying, "Your old radar transmitter was 60,000 watts peak. This new radar transmitter is only 100 watts; it won't attract lightning.

GB

Structural Failure Hardly
 

For Gerunf at Post 59, and all in this thread

Okay so structural failure of the vertical stabilizer is hardly likely.

Has anyone any thoughts on engine structural failures ?

Would not engine vibes tell the tale ?

Does the ACARS on this specific accident broadcast vibes data ?

Does the ACARS transmit in intervals ? One pilot forum commented it may be 10 minutes ?

I'd like to bring this thread BTTT with a question generated by comments on the R&N thread. I am surprised to discover that there is not just 'Alternate Law', but AL2 as well. Can someone explain SIMPLY what this does? I THOUGHT I understood the AB philosophy (a bit!) and that unless in 'Direct Law' you could not stall the a/c - in other words, despite bungling the hand flying, the FCC 'took care' of you and limited/adjusted your pitch. I read now on R&N (takata #2440) that this is not so and that AL2 has no such protection.

Q2: Is it correct that while (handflying) in AL(1) the FCC would adjust pitch (nose-down) if it sensed a large drop in airspeed towards the stall, or is AoA the over-riding trigger?

I suspect I'm going to get different answers to these questions from different folk - which would put me straight back on my 'bandwagon' about training not keeping up with systems.

Alternate Law
 

BOAC

Acc. to AMM:

-
The control law level which is:

No. 1: normal laws,

No. 2: alternate laws,

No. 3: direct laws, from the highest to the lowest level.


The law is such that:
-
each computer establishes the highest level of law (normal, alternate or direct) it can engage, taking into account the results of the internal monitorings and the availability:

. of the ADIRUs,

. of the control components,

. of the control surfaces, THS and slats and flaps.


-
among the computers which can engage the highest level of law , the computer having top priority is chosen (if only one computer is capable of the highest level of law , this computer is selected, whatever its priority level).



In FCOM is mentioned that ALTN LAW has 2 categories. ALT 2 would happen when U have an ADR DISAGREE>

With 2 ADR lost U have no HIGH AOA prot. anymore
with 3 ADR lost U have no HIGH SPEED prot. anymore

hope this helps :ok:

AOA Protection
 

BOAC
In ALT 1:

PITCH ATT is lost, HIGH AOA on ALT, but lost at loss of weight or slat/flap pos. failure.


Hope this helps as well :ok:

I don't think it has answered the questions? Let me try another way.

Does the FCC still have 'over-ride' on the control DEMANDS in Alt 1 and 2, and would either 1 or 2 command a pitch down if an impending stall was sensed, or, conversely, a pitch up with high speed?

Tyro - where are you?:)

Airbus Philosophy
 

BOAC

The answer is YES/NO. like written before:

in ALTN1 the AOA protection is there (till you lost weight or slat flap pos informations) and the EFCS protects and takes over.
in ALTN2 AOA PROT is gone when U have 2 ADR's faulty, HIGH SPEED at 3 ADR's faulty and the direct stick to surface so called direct LAW is working.

Old Boeing champ with yr FCC's:}

That's clearer, thanks. So in the AF crash, as we understand it, they would have been at Alt2 with no high speed prot? What, then, is the difference between THAT Alt2 and DL? EG Are there still pitch and bank or some other limits?

I knew this question would come :}

Before U lost the AOA/HIGH SPEED etc. due to this ADR failure U have still the LOAD FACTOR LIMITATION to +2.5g and -1.0g which is also lost in direct law.

FCOM
 

SmartCockpit - Airline training guides, Aviation, Operations, Safety


Check 1.27.30 pg1

rgds

Great link - thanks.

Well, in fact, there are two different AL's. But alternate in the correct sense doesn't exist at all! Funny to here that after so much squak?

AL is just a transitionary phase from normal to direct law. Actually, when you are in AL, you are direct law in roll and some (un)protected condition in pitch. To make it easier, AI called this mode AL. But generally speaking, there are only 2 laws, normal and direct. Which is completly logical: Eighter the computer does it, or you!

To make it even more complicated, there are two different AL! If you are still with me, continue to read: There is AL with protections and AL without. Pretty simple, when your computers still can deliver protections, they do, if they cannot, they don't. So it goes back again to the "AL doesn't exist" from above.

So, your question is: Do you have over- and underspeed protection in alternate law? Well, it depends. If you are in AL with reduced protection (that's what you mean by AL1 I guess), you still have low and high speed stability, and you have load factor stability. So in other words, you have it all (pitch-wise). In AL without proctection, you only have only load factor stability.

Or, in other words: In AL1 you still have all. Well, nearly all. In fact, you don't have anything. The trap is in the word "reduced" protection. As soon as you are in AL, the nice little green double bars at the speed tapes disappear, and amber X's are painted. This is a clear sign that you are not protected against high or low speed conditions. So you have to live with it.

If someone is still able to follow me, you are an Airbus pilot :ok:

Dani

- the thing that bothers some of us 'old-timers' is that probably even a lot of those won't be able to either!

that was one of my goals :E

No, really, jokes aside. It's pretty easy and everyone understands it, if you do a serie of sim sessions. I don't really know a lot of Airbus pilots who do not get it or do not like it. Even some B afficionados.

Dani

Email direct from the NWA pilot concerned.
The A-330 clearly has some problems that need to be corrected, poste haste.

PS:
Crew members names removed to protect confidentiality.

This being a technical forum you need to substantiate that with some technical points like why the A330 is a unique problem. Otherwise with just an opinion there is no room for discussion :)

How many other aircraft types, lomapaseo, have repeated problems with pitot probes icing up (or indeed, any other indicated airspeed difficulties) at altitude that you have heard about recently?

The latest incident with the referenced NWA A-330 has gotten the rapt attention of the FAA, you can be sure.
I would expect an emergency airworthiness directive to follow shortly.

No doubt that EASA and the FAA are looking at the design assumptions. But with all the sucesses of the various aircraft designs Boeings, Airbus etc. to accomodate this single system failure there's not a clear conclusion of a violation of the original certificate.

Now on the other hand if there is yet another combination that is at work here we do need to understand that and perhaps work that into our continued airworthiness fix.

Pitot Problems
 

@411A

Last week a Polnish B767 experienced some related problems. But I think that many incidents passed unrecognized, right now the industry sure is sensitized about 'pitots'. Seems to me also that the very achitecture of the A330 in respect of its FCC might have to do with it, as it is the most advanced.

Anybody to comment on the switching logic of the Antiicing System. I learned that the Ice Sensor is switching Pitot Heat to ~200°C inflight with the Antiicing Switch in 'Auto'? Switch to 'ON' would keep it at that value?

What would explain that the air became warm and humid all of a sudden?
There's no outside fresh air being blown directly in the flight deck obviously, so would the icing have also affected the packs operation? Could the heat exchangers have taken ice?

On the airbus, the probe heat computers manage the level of heating. Inflight, the pitots are heated to the high value. The position of the push button has no effect.

G'day bobrun,

I've experienced a marked OAT rise crossing the ITCZ many times, and in clear air occasionally, and sometimes the first indication is a sudden warming and stuffiness in the cabin. I don't believe it is the packs icing up just that they are not capable of the rapid response needed to counter such a quick OAT increase.

Regards,
BH.

Likewise....not at all unusual.

Rain with -21° ist not possible.

Time for some Met revision, Dani?

Surface crystallization of supercooled water in clouds ? PNAS

Supercooling Water - Video

Freeze Water in Seconds Supercooling - Video NB That was 5hrs at-18C

Mind you, not too many plastic bottles around (outside) at 35k.:)

It is worth remembering that water is one of the strangest substances known to man.

Thanks for the revision, Boac :ok:

Still I think it quite unlikely to see rain "streaming" around the windshield. Characteristical for supercooled water is that it freezes immediatly when it touches an object (the seed). Hence you cannot see if you have supercooled precipitation around you.

Anyway, all these incidents and one accident makes me think that with the change of earth's climate, we encounter stronger and different weather effects. I also count the BA 038 accident to these series, because they had unusual cold temperatures over Russia and the Scandies. Maybe we as pilots have to modify the way we look at weather.

Dani

The type of icing most likely in this/these incident(s) involved ice particle icing or glaciated/mixed phase icing. These relatively rare conditions are described in the report The Ice Particle Threat to Engines in Flight (page 13).

Reports of rain streaming around the windshield are discussed and clearly answered as being due to the ice particles melting on the anti-iced surfaces. The conditions are outside of the conventional airframe icing boundaries, thus no airframe icing is seen. Also, note that the conditions are near, or above large Cb build-ups; the aircraft are not necessarily in Cbs.
I have encountered these conditions during test flights in 1997 (tests preceding those referenced in the report - USA 1998). On occasion small ice build-ups could be seen at the windshield edge or on the windscreen wipers - the windscreen was very wet.
Also, the IMC described in the report is often very thin cirrus cloud, which many pilots would declare as VMC due to the apparent good visibility.

The mechanism of pitot icing (AF447) is probably similar to TAT probe icing, or where the pitot is considered to be a very small scale engine. Ice particles, slowed by bends in airflow ducts, melt when in contact with heated surfaces, and the water acts as the glue for more ice particles to accumulate and freeze, which in time exceeds the heat-flow capability of the anti-icing structure; the report gives details – I urge all pilots to read the details.

Re “What would explain that the air became warm and humid all of a sudden?”.
As a hypothesis, perhaps encountering an ice particle cloud (high ice water content) where the melting ice and changes in heat flow are beyond the instantaneous dynamics of the Air Cond packs. The report cites the possibility of very high Ice Water Content, as a guide, a mid value of 4gm/M^3 would require a stout umbrella at ground level if transformed to rain.

Re “Maybe we as pilots have to modify the way we look at weather”. I agree.
Other sections of the report (page 17) discuss the shortcomings of radar in detecting ice particles and hence the inability to see the high altitude structures of Cbs, or new, emerging build-ups in the general cloud mass or anvil.
Defensive strategies include avoiding the core of large storms by a very wide margin, remaining upwind to avoid the anvil region, and being aware of new build-ups.
We must reconsider the way we look at very large storms; the judgment of size might be subjective, similarly ‘a very wide margin’ involves judgement and decision making processes.
My experiences indicate that the risk of encountering conditions favourable to malfunctions are present up to at least 30nm from a detectable Cb core, thus with a margin of safety, 50 nm should be considered – this consideration should also include turbulence. We need to focus more on planning ahead - rerouting, use of satellite pictures, and reasoned judgement of met forecasts – know before you go.
On two occasions during test flights, super, ‘super’ cells were seen – so large (area, height), so black, and so menacing, that ‘evil’ was a worthy term. These storms were not investigated during the tests and were avoided by 100 nm.

safetypee, thanks for that very enlightening post.

Re-Ordere ACARS Messages
 

Having kept a close eye on a.net forums, I have noticed that two pilots who regularly post sane comment about this issue have done a lot of work to try and figure out what may have happened.


One poster (Mandala499) who is probably the most sane guy there, has done a good job of trying to figure out the timeline of the ACARS messages and re-order them according to their respective time stamps.

I have shamelessly (sorry Mandala) copied his good work here in order that someone on PPRuNe may make more sense (or gain a better insight) as to what went on at the time these messages were sent?

This is the list reordered...

0209 START
0210 34-11-15-0 FLR EFCS2
EFCS1, AFS - PROBE PITOT 1+2/2+3/1+3 (9DA)
9DA=HEATING ELEMENT PITOT 1 (6DA1/PHC1)
Heating Element Pitot 1 suspected failed.

0210 27-93-34-0 FLR EFCS1
EFCS2-FCPC2(2CE2) WRG:ADIRU1 BUS ADR1-2 TO FCPC2
No Data from ADIRU 1, ADR 1 & 2 no sending signal to FCPC2
No ADR Data from ADIRU 1 to PRIM2.

0210 27-90-45-5 WRN MXSTAT
EFCS1
ERROR NOTICED - Air Data Fluctuation/Inconsistency

0210 27-90-45-0 WRN MXSTAT
EFCS2
ERROR NOTICED - Air Data Fluctuation/Inconsistency

0210 22-10-00-0 WRN AUTO FLT
AP OFF
Autopilot Shut off for safety, result loss of 2 Valid Air Data Channels.
This prevents faulty Air Data from affecting autopilot into making the wrong actions.
Commence AP/FD FAULT ISOLATION PROCEDURE
System Filter & Check:
- DISAGREE AOA Sensor Data in FCPCs
- DISAGREE PITOT PROBE Data in FCPCs
- FAIL ADIRU 1 and 2
- FAIL ADIRU 1 and 3
- FAIL ADIRU 2 and 3
- FAIL ADIRUs

0210 22-62-01-0 WRN AUTO FLT
REAC W/S DET FAULT
Loss of 2 ADRs, autopilot cannot provide Windshear Protection.

0210 27-91-00-5 WRN F/CTL
ALTN LAW
2 ADR REJECTED, NAV DISAGREE NOT YET CONCLUDED - FAULT ISOLATION IN PROGRESS

0210 22-83-00-2 WRN FLAG
LEFT PFD LIMIT
Rejected ADR still feeding data to PFD
If there is valid ADR, it's not being selected for LEFT seat.

0210 22-83-01-2 WRN FLAG
RIGHT PFD SPD LIMIT
Rejected ADR still feeding data to PFD
If there is valid ADR, it's not being selected for RIGHT seat.

0210 22-30-02-5 WRN AUTO FLT
A/THR OFF
Autothrust Shut off for safety, result loss of 2 Valid Air Data Channels.
This prevents faulty Air Data from affecting Autothrust into making the wrong actions.

0210 34-43-00-5 WRN NAV
TCAS FAULT
Loss of ADR1 to Transponder 1 (if selected) or Loss of ADR2 to Transponder2 (if selected)
Loss of Mode C.
This is downstream of loss of ADR.

0210 22-83-00-1 WRN FLAG
LEFT PFD NO F/D
Automatic Flight System (AFS/FMGC) loss of 2 ADR sources.
Safety mechanism, prevents erroneous F/D for pilot to follow

0210 22-83-01-1 WRN FLAG
RIGHT PFD NO F/D
Automatic Flight System (AFS/FMGC) loss of 2 ADR sources.
Safety mechanism, prevents erroneous F/D for pilot to follow

0210 27-23-02-0 WRN F/CTL
RUD TRV LIM FAULT
Loss valid of ADR Data (require 2 ADRs) for FMGC/AFS
FMGC Flight Envelope Module locks in Rudder Travel for safety.

0211 34-12-34-0 FLR IR2
EFCS1X,IR1,IR3, ADIRU2 (1FP2)
ADIRU2(1FP2) - ADR2 self monitoring & PHC rejects own data
Loss of discrete data from ADR2 = PITOT 2, STATIC 2L, STATIC 2R, TAT 2, AOA 2.
NAV DISAGREE CONCLUSION DELAYED - ADDITIONAL FAILURES - RECOMMENCE FAULT ISOL

0211 34-12-00-0 FLR ISIS
ISIS (22FN-10FC) SPEED OR MACH FUNCTION
SUSPECT LOSS OF ADIRU1 AND/OR ADIRU3 FOR ISIS MACH
Suspect Loss of ADIRU3
NAV DISAGREE CONCLUSION DELAYED - ADDITIONAL FAILURES - RECOMMENCE FAULT ISOL

0211 34-12-00-1 WRN FLAG
LEFT PFD NO FPV

0211 34-12-01-1 WRN FLAG
RIGHT PFD NO FPV

0212 34-10-40-0 WRN NAV
ADR DISAGREE
NAV DISAGREE DISCOVERED - FAULT ISOLATION COMPLETED
Due to no further ADR faults occuring.

0213 27-90-02-5 WRN F/CTL
PRIM1 FAULT

0213 27-90-04-0 WRN F/CTL
SEC1 FAULT

0213 22-83-34-9 FLR AFS
FMGEC1(1CA1)

0214 34-10-36-0 WRN MXSTAT
ADR2
RESULT OF 32-12-34-0

0214 21-31-00-2 WRN ADVSRY
CABIN VERTICAL SPEED
LOSS OF ADR DATA

Open to comments?

there's this:

Desert Dawg citing Mandala499

Impressive work !

Following this reading, there is a question I have been wondering about for weeks, and now is the time to ask :

what is the precise difference between a NAV ADR DISAGREE (which we have in the AF447) and a F/CTL ADR DISAGREE (which we have in all the other instances) ?

Thanks for your help.

@Svarin,

I hope Mandala reads PPRuNe as he may be the person to answer this?