Clandestino

The same way the AF447 thread got into its 12th incarnation - by liberal application of wishful thinking.

DozyWannabe

Because, in a regulatory sense, the Thales AA pitot tube was still technically fit for purpose. Have a look at this article from 2009:

Airbus backs overhaul of pitot icing certification standards - 12/13/2009 - Flight Global

So while EASA's certification criteria were less up-to-date than the FAA's, it would appear that even the later FAA standard does not take this form of icing into account, and consequently the Thales AA pitot probe would have passed certification in the US too.

Closer to 30, and not all of them involved the Thales probes, the Goodrich models could still have issues if the conditions were severe enough. Avoiding bad weather in an aircraft is not just for the sake of not wanting a bumpy ride!

Ultimately, prior to this accident the aviation industry did not consider temporary loss of airspeed indication to be a significant threat - just set pitch and power if necessary and the aircraft will take care of itself until the blockage clears.

In a purely technical sense, this aircraft did not crash because of the blocked pitot probes, it crashed because the instinctive reaction of the pilot flying was inappropriate - and this was not caught and corrected by the rest of the flight crew.

PS: Winnerhofer, you seem to have an intense personal animosity towards the French authorities - how come?

john_tullamarine

Folks, I appreciate that feelings can run strong and that this topic, in particular, is of great interest to us all.

However, it is not our place here to have discussion extending to an aggressive and, potentially, legally risky level.

Please consider posts carefully lest I be forced to wield a sword.

DozyWannabe

It'd be nice to have a bit of a summary in English, I must say.

Correct me if I'm wrong, but as far as I can make out, the author of the slide set seems to be arguing that prior incidents warranted more action from the DGAC earlier, that the BEA should have made a public report on the issue and that AF and Airbus should have forced the pitot tube replacement earlier.

All these things are definitely worthy of consideration with the benefit of 20/20 hindsight, but it doesn't take into account the point I repeated earlier, namely:

The slide set itself quotes the FSF as saying there were 300 accidents and incidents involving flight instrumentation issues from 1989-1999. The Thales AA probes were only offered as an optional fit to the A330/340 from 1999 onwards I believe, so the author is misrepresenting a more general statement as something specific to this case - i.e. none of those 300-odd incidents involved the Thales AA probe.

DozyWannabe

Actually I don't remember the specifics. Could you dig the references up for me?

What I'm pretty sure of is that this is the only commercial accident in the last 25 years involving loss of/faulty instrument indications where airspeed was the only thing lost. Others involved additional factors such as false overspeed warnings (and consequent AP pitch-up), or faulty altimeter readings.

The regulators are *part of* the industry.

[EDIT : Winnerhofer:

First, I'd recommend that you don't post links directly to MS Office documents (such as PowerPoint files), as they have been known to contain malware - see if you can find a web-enabled link in future if you can.

I did upload it to my Google Drive and had a look, and as far as I can tell it's yet more SNPL nonsense. The author of the PowerPoint is basically arguing that the crew were handed what he calls "latent conditions" specifically by Airbus, AF and the French authorities. He links an unrelated 2002 piece in which the aircraft is expected to leave the flight envelope to the AF447 conditions in which it was not. It left the flight envelope because of the actions of the pilot flying.

He also infers that:
- The BEA should have investigated earlier incidents because the AF crew called a Mayday in one of them. As far as I'm aware a Mayday call does not automatically trigger an investigation by any investigation agency I know of.
- The BFU and NTSB recommendations applied to the Thales AA pitot probes alone, when they did not.
- The ETSO C16 standard was expected to be replaced with one which included mixed conditions and ice crystals, which it was not (see my post #232)

DozyWannabe

It's a bit hard to follow you if you just post links without commentary of your own. I'm wondering why you've stopped using your own words.

The "approach to stall" focus as opposed to "stall recovery" prior to AF447 was a global issue, not just one restricted to France.

jcjeant

Actually I don't remember the specifics. Could you dig the references up for me?

DozyWannabe

As far as I can tell, project ADELINE was actually a joint commercial/academic research programme to find possible *successors* to the existing pitot-static/vane technology. The fact that the online references to the project seem to have disappeared over the last few years seems to indicate that they couldn't find one that was practical at this stage.

jcjeant

Yes indeed but the important point in regard of this:
is this (bold)
And
So in fact the aviation industry (and regulators .. part of it) considered the temporary loss of airspeed like a threat IMHO

DozyWannabe

@jcj:

I think the qualifying words are "The loss of *these* data" - meaning more than one of them [EDIT : and as if789 correctly points out below - permanently], an example of which was the Aeroperu 603 accident. Or a situation where loss of one has knock-on effects (like Birgenair 301). As long as you're (relatively) straight and level, temporary loss of airspeed data can be easily overcome by using pitch-and-power, which is the reason smaller aircraft which don't have any redundancy in the pitot-static system can still pass airworthiness requirements.

In short - the temporary loss of airspeed indication *alone* was not considered a threat because there were long tried-and-tested workarounds.

Regarding the FAA's point on replacing the Rosemount units, I'd like to see the original document if anyone has a link handy. They may have been thinking along the lines of Birgenair, where a blocked pitot tube on one side caused the automation to pitch the aircraft up to the AP pitch/AoA limit due to a false overspeed condition. Even in that case the aircraft only departed controlled flight when the PF (Captain) pulled the throttles back to further reduce speed and immediately put the AoA into the stall regime.

The Airbus systems automatically disengage autoflight if the data from the three pitot sensors disagree, so a similar situation would not happen there.

infrequentflyer789

{ been away for while, come back and found there is still a 447 thread -
but, unexpectedly, with interesting and new information }

There is a key difference in the statements: "temporary loss" and "loss" (not temporary).

Taped-over static ports, wasp nests in pitot tubes, and in fact probe icing due to inadequate or failed heating (for example) are not temporary - and had caused crashes prior to AF447.

Incidents where working pitot heaters were overwhelmed for a few seconds, 447 and similar previous, were clearly temporary and could legitimately have been regarded very differently in terms of risk/threat.


Except in 2008/2009 EASA responded to DGAC that there was not an unsafe condition that warranted mandatory probe replacement. See the slides linked to further up the thread, Présentation "Accident AF 447 228 victimes Comment fut traité le. RETOUR DEXPERIENCE. par : 1AF447-REX." - slide 42, for one reference. Note: strictly, they did not say there was not an unsafe condition, only that there was not one that was significant enough to warrant mandatory action.

Since EASA is part of the industry, clearly the industry was at least not-unanimous on whether or not temporary loss of airspeed was a threat.

Turbine D

Dozy,
Here is a link:

AIRBUS INDUSTRIE Model A300 Series Airplanes

The AD didn't mandate replacement of the Rosemount pitot tubes, just modification of the pitot probe heater within 1800 flight hours. This applied to the A-300 aircraft.

DozyWannabe

Thanks TD, but this seems to be a different case - jcj was taking about A330/340 aircraft in 2002 rather than A300s in 1983.

Cheers for looking that up though - it's interesting nonetheless!

Turbine D

Dozy,
I went through all 2002 FAA Airworthiness Directives (AD's) on the FAA site and there were none regarding Rosemount pitot tubes and/or replacements on A-330s, A-340s or any other Airbus aircraft.

Sorry about the first search, I did it by appliance, not year, and that was the only one that came up…

DozyWannabe

Right - I think there are definitely some crossed wires going on somewhere...

Cheers again for having a look!

roulishollandais

Misunderstanding of the report, of PF vs PM, of position of pilots vs seats, of Crew hierarchy vs seats, of seats pictures in the report. Perhaps Hospital has more to learn from normal aviation uses than from controversary crash CVR.
But exchanging and taking time for reflexion is always difficult but positive.

DozyWannabe

Yeah, that write-up gets quite a few things wrong - and says other things which are at best debatable. Safety processes used in aviation making their way into healthcare is nothing new, mind.

PerAsperaAdAstra

This may be a dumb query, I fly small stuff for my daily crust, but, 447 and I think it was Condor Air accident Blocked (static ports) interest me. I can understand at alt airspeed in terms of Mach No is important, due to overspeed with Mach crit causing buffet etc. However why does the computer air data program attach quite so much importance to pitot static airspeed? If you have an AOA reading, it just seems to me if the system was programmed to follow the age old Golden Rule of Power+ Attitude=Performance, surely both of those accidents may not have occurred? Again power setting coupled to an AOA readout, would that not be a pretty reliable system as a backup?

I know in 447's case it was complicated by the flight mode it defaulted to, trimming the stab fully nose up, best chance for recovery was at incipient stage, just release back pressure, if only they had known, once in a fully developed deep stall, it would have taken some radical pitch attitudes to recover, at night IMC, not understanding what was happening, that would be a big ask of any crew.

DozyWannabe

Well, to be fair the trim was only increased to full nose-up because that's what the pilot was demanding of it through the sidestick.

I was wondering if you could clarify a bit what you meant by "...why does the computer air data program attach quite so much importance to pitot static airspeed?".

If you're talking about in terms of the autopilot, it makes sense to automatically disengage it in the event of UAS condition because bad data can cause the AP to pitch the aircraft inappropriately (as in the case of Birgenair 301).

If you're talking about the FBW systems, the only thing they really lose in terms of protection is the hard protections - this is because the pilots should have full authority - introducing bad data to the systems could have unintended negative consequences.

DozyWannabe

"Another AF447"? Not even slightly.

In that case the aircraft pitched up as a result of the turbulence itself - the crew correctly tried to counter the pitch with nose down and control the airspeed (the indications remaining OK in this case). The temporary "loss of control" was due to external factors, unlike AF447 where the pilot flying stalled the aircraft and subsequently lost control.