AF 447 Search to resume (part2)

[Turbine D]

tubby linton

A good simple summary as to what happened at altitude in my mind. The burning question is: Why did they elect to fly through the CB in the first place?

TD

[RR_NDB]

ULB detection

With this 1% duty cycle (specified for battery life), very probably:

1) They used RC oscillator (frequency dependent on batt. voltage) at TX
2) Peak detector at RX
3) Conventional RX front end BPF (not a very sharp one)

Conclusion:

Clearly there is room for improvement for much better ULB systems than the current std.

PS

The DSP examples i presented are not "well suited" to "short pulses" (short ones compared to the pulse repetition period).

The DSP technique probably was the one allowing Orion P3 based in Moffet Field, locate through sonobuoys the USSR subs in Pacific ocean. The sub propeller shaft generates a continuous "signal" allowing a good RX S/N ratio through DSP. The Orion as a signal repeater to remote powerful computers.

Mac

[jcjeant]

Hi,

Why did they elect to fly through the CB in the first place?

So far we can ask why they fly through the CB in the first place ?
Methink .. at today time .. "elect" is a speculation ...

[takata]

Originally Posted by promani

takata
Medical and Pathological Information
Sailors from the Frigate Ventôse recovered about thirty bodies. A visual examination of the bodies showed that they were clothed and relatively well preserved.
This would contradict most of the press releases (still today summaries):
1. Many bodies were recovered by the French Navy (about 3/5th by Ventôse);
2. They were clothed and well preserved

A bit confused by this. Unable to spot the difference, or are my eyes failing me?

The difference is to be find in the previous few pages were we discussed the "fact" that all passenger corpses recovered by the "Brazilian Navy" were "unclothed".

[rh200]

Signals 20 dB or more below the noise floor can detected using this method!

How accurate is the cycle, one could imagine using pulsar detection algorithims. Another words folding the data in time over the the full pulse cycle, the noise should decrease with a root two factor.

[Turbine D]

Hi,

Methink .. at today time .. "elect" is a speculation ...

I don't want to get into an English word debate with you, but elect = choose = decide. The fact is they proceeded to and did fly into the CB, it is not speculation. What is speculation is the answer to the word, why at the moment. We don't know but we can speculate, can't we?

[takata]

Originally Posted by tubby linton

Imagine the folowing scenario- pitots ice up generating an overspeed. The aircraft pitches up and the athr retards the power to idle,add in a powerful upcurrent as a cb is penetrated adding to the pitch up. The aircraft has a lot of energy and due to the big wing a lot of manouvrability at altitude Whilst the crew is reacting to the autopilot dropping out and the aircraft fbw law degrading the aircraft stalls. If the aircraft has been cruising at 15-20kt above VLS and assuming a rapid decelleration the crew may have had only ten seconds or less to counter the stall but having penetrated a cb they are still in an updraft. The aircraft continues to climb. The crew pitch down to counteract the stall but the speedtape is still showing an overspeed. VLS is now overlaying the Barbers pole and the crew struggle to interpret what what has happened.Their computerised FBW protected aircraft had turned against them.
The cockpit is full of warning chimes and the ecam is full of failure messages due to the icing up of the ADR. The aircraft exits the CB core and is still in a
stalled condition but now is in the downdraft of the CB and it rapidly descends towards the sea and to their demise

I'm feeling that we are now back to the early discussions we had two years back, right after the crash.
If one really want to have his "FBW upset" fitting into those five minutes flight while covering less than five Nautic Miles, one would have to make a big distortion of everything in order to fit well into his thesis.

Here are the main ingredients for your catastrophe dish:
* First, you'll need an incompetent crew (the one flying blindly straight into a giant storm);
* Second, you'll need a bunch of incompetent designers (for all those unreliable flight envelope protection systems);
* Third, you'll need a good deal of very bad luck convenientely applied with the right timming (updraft here, downdraft there, and bits of ice scattered over the whole dish).

As a matter of fact, pitots icing at FL350 would not instantaneously switch the airspeed from Mach 0.82 to Mach 0.87, triggering a pull up to 60,000 feet (due to rogue C-3PO in command), then declare all the pitots frozen, then quit, handling over the whole situation with zero speed left (but displaying mach 1 and 90 degrees AoA) to the poor doomed crew which will try to figure out what to do next into the storm until contact with the ocean surface, flying backward, tail first, as per Bearfoil's analysis.

S~
Olivier

[jcjeant]

Hi,

choose

You have a choice (ability to choose) when you have to decide about different options
You can't be sure (actually) that the pilots have to "choose" if they had seen nothing dangerous waiting them on the path.......
Hence my emphasize on "elect" ... no more no less.

[takata]

An example taken from the Boeing article I already linked here: AERO - Engine Power Loss in Ice Crystal Conditions

One can see from the temperature legend that the white part at the top of this tropical cloud (a fully developped typhoon) is below -70°C while the aircraft path (stars) is right in the middle of it.
Nonetheless, see below the flight conditions reported during the descent into Taipei.

INFRARED IMAGE WITH AIRPLANE TRACK
In this infrared satellite image from about the time of an engine event, bright white indicates colder cloud, and therefore at high altitude. The airplane penetrated the upper altitudes of a fully developed typhoon, yet the pilot did not see any flight level radar returns. The asterisks represent the aircraft path from left to right on descent into Taipei, with the event noted in purple.

• A commercial airplane on descent, flying in convection conditions, experienced a TAT anomaly. (The anomaly is due to ice crystals building up in the area in which the sensing element resides, where they are partly melted by the heater, causing a 0 degrees C reading. In some cases, TAT has stabilized at 0 degrees C during a descent, and may be noticeable to pilots. In other cases, the error is more subtle, and not a reliable-enough indicator to provide early warning to pilots of high concentrations of ice crystals.)
• At 38,000 feet (-42 degrees C), the pilot encountered moderate turbulence and noted some lightning in the vicinity.
• A brief power-loss event occurred at 30,000 feet — the engines restarted quickly.
• There were no radar echoes at the altitude and location of the airplane.
• An absence of a response from the ice detector indicated that no supercooled liquid was present.
• The pilot reported heavy rain at -25 degrees C.
• Initial report of rain on the windscreen was later determined to be ice crystals, and confirmed by the pilot to have a unique sound.

[Machinbird]

* First, you'll need an incompetent crew (the one flying blindly straight into a giant storm);
* Second, you'll need a bunch of incompetent designers (for all those unreliable flight envelope protection systems);
* Third, you'll need a good deal of very bad luck convenientely applied with the right timming (updraft here, downdraft there, and bits of ice scattered over the whole dish).

As a matter of fact, pitots icing at FL350 would not instantaneously switch the airspeed from Mach 0.82 to Mach 0.87, triggering a pull up to 60,000 feet (due to rogue C-3PO in command), then declare all the pitots frozen, then quit, handling over the whole situation with zero speed left (but displaying mach 1 and 90 degrees AoA) to the poor doomed crew which will try to figure out what to do next into the storm until contact with the ocean surface, flying backward, tail first, as per Bearfoil's analysis.

Takata, take a deep breath and turn your internal critical judgement filters back on.

Bearfoil's concept is a wild hare and should be disregarded. We do have actual wreckage this time and it is located very close to LKP pretty much down track, and indicating a descent to the water that almost guarantees it was in a deep stall. The aircraft is not supposed to fall out of the sky while in full cruise, and the flight control system is designed to guard against departures from controlled flight, so something undeniably happened that the flight control design folks did not forsee.

Tubby's concept may be slightly over-elaborated but has significant potential to explain what happened. Your expectations of engine stall at high AOA may be unreasonable.

About the best we can do with the data we have is try to match endpoints and any event data that ACARS provided until we see actual aircraft data.

It all fits in a context. AF447 did not do the impossible. We just have to be clever enough to figure out how it did what it did.

[auv-ee]

Originally Posted by RR_NDB

1) They used RC oscillator (frequency dependent on batt. voltage) at TX
2) Peak detector at RX
3) Conventional RX front end BPF (not a very sharp one)

We speculated a long time back about whether the pingers have advanced to crystal oscillators or are still using RC or LC oscillators, and whether the ping rate is digitally divided or runs from a separate oscillator. I don't recall any resolution of that. The required spec is 37.5 kHz ± 1 kHz; I only hope the pingers are really better than that.

Conclusion:

Clearly there is room for improvement for much better ULB systems than the current std.

We can all agree on that.

Originally Posted by rh200

How accurate is the cycle, one could imagine using pulsar detection algorithims. Another words folding the data in time over the the full pulse cycle, the noise should decrease with a root two factor.

We don't know (see above), but if it is stable, this might be done (root(n) noise reduction). I had speculated in my original post on this subject (#951 in the second thread) that something like this might have been done with the data from Emeraude. It was just a guess, I don't know what they actually did.

[auv-ee]

ULBs and recorders

An excerpt from the following article in Aviation International News:

Investigators Hope Recovered Flight Data and Cockpit Voice Recorders Shed More Light on AF447 Crash: AINonline

"Meanwhile, the secretary general of the international civil aviation organization (ICAO), Raymond Benjamin, last week restated the goal of increasing the endurance of underwater locator beacons (ULBs) from 30 to 90 days and increase the range of the ULB signal from one to four nautical miles with existing and mature technology. The technology needed to develop systems to eject floatable recorders upon impact also already exists. In the longer term, ICAO hopes to see aircraft transmitting flight data on a continuous or event-triggered basis."

[oldengmkr]

Agreed, AF447 did not do the impossible.

Machinbird,

The A340 scenario, with a zoom climb resulting in decreased forward velocity followed by a deep stall, with perhaps even a tail down fall to the water, fits the roughly known envelope of AF 447. There does not seem to have been any aspects of this irrefutably rejected by the responses and counter comments provided to date in this thread - or did I miss something?

[FlamantRose]

mm43

With reference to :

"ballonné et endommagé par la morsure de requin étrange"

My suggestion is that there is a comma missing after requin (otherwise it doesn't mean anything in french). Obviously this "requin" cannot be strange or odd ! It's the facts that are strange. It would then read "ballonné et endommagé par la morsure de requin, étrange !" and could be translated by :

"swollen and injured by a shark's bite, strange (peculiar)".

Does this look any better ?

[Machinbird]

oldengmkr

The A340 scenario, with a zoom climb resulting in decreased forward velocity followed by a deep stall, with perhaps even a tail down fall to the water, fits the roughly known envelope of AF 447. There does not seem to have been any aspects of this irrefutably rejected by the responses and counter comments provided to date in this thread - or did I miss something?

I posted a reference to a simulator demonstration last year with this same type scenario, and in the intervening period, no one has absolutely refuted it as a possibility other than asking how the airspeed could increase with a blocked pitot. I believe once that was explained, there were no further significant reservations. The one reservation some of us have with this scenario is that you would expect the Rudder Travel Limiter to be set at a different travel than found unless some remarkable coincidences occurred.

I hope by tail down you mean a slight positive pitch attitude relative to the horizon, not a tail slide.

[mm43]

FlamantRose;

I think the "odd" represents something that is "random". So, the English would equate to, "bloated and injured by random shark bites". That's the problem with translating and comes down to, e.g. "the sky is blue", compared with, "blue is the sky". Which one is right?

Anyway, the word "relatively" used in the BEA report can be construed differently, and your understanding will be guided by your "knowledge and experience".

[takata]

Originally Posted by Machinbird

Bearfoil's concept is a wild hare and should be disregarded.

Many odd concepts are strangely resurfacing and some progress are unduely discarded while, at the same time, we are closer from knowing the truth from the inquiry. Hence, I'm a bit cynical and sceptical of the reaction if it won't fit those "deep stall from FL350" theories.

Originally Posted by Machinbird

We do have actual wreckage this time and it is located very close to LKP pretty much down track, and indicating a descent to the water that almost guarantees it was in a deep stall.

Maybe, maybe not, and I believe more the later.
But then, my point is that if she was in a "deep stall" situation, she certainly has not departed at once from cruise level (or even higher) at 0210 (or even earlier). A four minutes and half ride of "deep stalling" would have to start above 80,000 feet in order to fit with a crash time post 0214:26. Then how the hell would she have reached such a level flight?

At best, a single unrecoverable upset would have started 90 or 120 seconds later than 0210. But now, the distance finally covered would be puzzling (but who knows which exact track she has actually followed down to the sea!).

But those 90 to 120 seconds would have been all in ALT2 Law. Here, it is not so hard to understand that an aircraft deprived of most of its protections against "abnormal attitudes" might more likely "upset" in certain conditions than when it was flying in "fully protected mode" (before 0210).

Originally Posted by Machinbird

The aircraft is not supposed to fall out of the sky while in full cruise, and the flight control system is designed to guard against departures from controlled flight, so something undeniably happened that the flight control design folks did not forsee.

This "something not foreseen" is very likely the consequence of more than one event, a chain of events, rather than this simple "computer glitch" explanation which looks much more like a greviance against all those computerized automatisms, by principle, rather than a fully reasonned analysis. Hence, me being cynical/critical about this stance.

Originally Posted by Machinbird

Tubby's concept may be slightly over-elaborated but has significant potential to explain what happened. Your expectations of engine stall at high AOA may be unreasonable.

Tubby's concept is not only slightly over-elaborated, it just doesn't fit with many facts. My point about the possibility that engines would have experienced some notable troubles during such "4.5 minutes deep stall" is only one amongst many others in opposition to such conclusion.

The process of the pitots icing at cruise level is now well documented for the A330 family: no event ever caused an excess airspeed reading. In fact, the contrary: a drop of airspeed (down to 60 kts) followed by a possible (and false) low speed "stall" alarm. Hence, if a rogue C-3PO would become confused, it would trigger a nose down order instead of a zoom climb!

Anyway, he could only be confused by a very slow build up of ice, then he would never recognize the truth, then, never trigger an UNRELIABLE A/S at all.
Nonetheless, you would have the risk of a very different "upset" in perspective (an high speed stall) and not a "deep stall".

The recovered RTLU (Rudder Travel Limiter) settings are showing Mach 0.82 at 0210 (when it faulted due to this unreliable airspeed). It is neither Mach 1 nor 60 knots, but the current cruise speed planned at FL350. Consequently, we may be 99.9% sure that those faulty airspeed imputs were correctly detected by the system when the aircraft was not stalled in either way, being still at cruise level and not in an abnormal attitude up to this point. The following system action was then, as per design, to revert to ALT2 Law by turning off all those affected protections, Hence, avoiding to trigger a false "protection" due to those unreliable airspeed data.

Originally Posted by Machinbird

About the best we can do with the data we have is try to match endpoints and any event data that ACARS provided until we see actual aircraft data.

It all fits in a context. AF447 did not do the impossible. We just have to be clever enough to figure out how it did what it did.

Correct. Let's try it then.

S~
Olivier

[Turbine D]

takata

Here is part of an old post (5/26/2010) by machinbird that you might want to consider:

Quote:
Pitot Ice

Pitot probes have a liquid drain (bleed) hole, whose air bypass has to be accounted for in the airspeed calcuation. Clog the drain, and pitot pressure rises, giving erroneous high airspeed. Indeed, per reading in this thread, some of the earlier Airbus pitot malfunctions were with poorly manufactured drain (bleed) holes.

Add more ice, and you clog the pitot head itself, and then pitot pressure will lock, or will decrease if there is any drain opening at all.

GB
Prior incidents of A330 pitot icing have resulted in overspeed warnings as well as low airspeed warnings.

But look at this post by Jeff (Hyperveloce) on the 9th of July!! #3397.
Quote:
Out of the loop ?

A contribution by Pilotaydin, on the Airliners.net forum (Pitot freezing=>overestimated airspeeds=>nose up=>stall):
__________________________________________________ __________________
I would like to share a small story about something i experienced in the sim a while back, as a demo from my instructor towards the pros and cons of fbw and envelope protection...

we "flew" through an area of icing in the sim, the probe heat function and the airbus a/c itself is designed to fly through known icing, however, that doesn't mean it can withstand anything put in its path... our pitots iced over and our airspeeds started indicating 300+ at high altitude, which is bad news, because we're passing Mmo and Vmo, so the a/c as per design pitched up.... after about 20 seconds of this, as the speed wasn't decreasing, we were actually stalling and losing altitude, and the sidestick = useless, it wouldnt let any one of us pitch down, we started a large rate of altitude loss. Even if we disconnected the a/thr system and idled or added full power, the damn nose was pitched up....we went down 30,000 feet into the water outside jfk in the sim....during that descent, nothing came up on the ecam, just the warning chimes of overspeed.......we of course didnt just sit there, it was a demo we were observing he different things going on...at one point my hand did go up towards the PRIM 1 and PRIM 2 computers...i thought maybe if i let them out of the loop, we could go to altn law but i decided not to intervene to see the outcome....
knowing your systems helps, and the a/c doesnt always provide an answer to us....

Things need interpretation and over automation sometimes leaves us out of the loop...the other day over the atlantic, at 35,000 feet, we got master caution chime that said :
Start valve open and it asked us to switch off the bleed to one engine....leaving us with only one bleed left over the atlantic....are you gonna follow the ecam? or are you going to emergency cancel it?
__________________________________________________ ___________
btw, I don't get how a Pitot obstruction only (of the ram port/the drain) can lead to overestimated airspeeds (and possible overspeed alarms): if the dynamic pressure cannot be overestimated (?), then it has to be the static pressure which is underestimated (?) and this would imply that the static ports are also blocked and that altitude has been lost since their blockage ? Is that so ? Would there be other ways to overestimate airspeeds ? On the contrary, a blocked Pitot ram port is sufficient to roll back the airspeed to 70-80 kts.
Jeff

[takata]

Originally Posted by Turbine D

Here is part of an old post (5/26/2010) by machinbird that you might want to consider

I know this story from day 1 when this e-mail circulated (a friend of mine, who's got a friend who's got a friend who recieved it and shared it).
Instead of sim hoax, read the real an live reports about unreliable airspeed events at cruise.
Undetected build-up => NO UNRELIABLE AIRSPEED TRIGGERED, no switch from direct law to ALT, no RTL control fault, no PITOT PROBE fault, No PFD Fault, etc.
If airspeed reached Mach 0.87 and triggered a nose up order, why the RTL settings would still show Mach 0.82?

Think about it.
S~
Olivier

[Machinbird]

You are right Takata. I think I'll have to ease up on Bear a bit. I fully agree with this view of his, at least in the latter stages of the fall to the surface. Earlier, I am not so sure.
Bearfoil

not even bear thinks this airframe had greater than 90 degreees of AoA ('backward' flight)...

Have you a scenario that fits the endpoints? AF447 has been an enigma from the start. The only thing I know for certain is that Newton's laws were not repealed.
Takata

Tubby's concept is not only slightly over-elaborated, it just doesn't fit with many facts. My point about the possibility that engines would have experienced some notable troubles during such "4.5 minutes deep stall" is only one amongst many others in opposition to such conclusion.

Well lets get started. Let's examine these facts.
My favorable experience with jet engines at high AOA does not include experience with Fan type wing mounted engines. Why are Fan type engines so much more finicky (if they indeed are)? And as always, others are welcome to join in.