AF 447 Search to resume

[itsmepaul57]

AF447

Maybe a much more useful device - inview of the fact that the earth is 72% water - would be a CVR that was stored in the top of the fuselage above the passenger cabin that ejects on contact with water and maybe with a pressure sensor after a certain depth - bright orange flashing strobes and powered by sunlight, floats to the surface for retrieval by rescue units. (too simple?) PE

[good spark]

paul
you have a vivid imagination
keep taking the pills

[asc12]

Originally Posted by HazelNuts39

All things combined, the conclusion could be that it is not likely that the airplane stalled at 2:10, and remained stalled all the way down to the surface.


Regards,
HN39

Just for clarification, would you say that it is unlikely that the airplane stalled at all, or that it is unlikely that the airplane BOTH stalled AND remained that way to the surface?

It seems to me, unencumbered as I am by much knowledge of Airbus FCL, that it isn't surprising at all for an airplane with unreliable airspeed information in rather rough weather to reach a critical AOA.

From that point, however, no plausible explanation as to how the aircraft reached it's present position has presented itself (to me), even after several hundred pages of more-or-less educated speculation.

[CONF iture]

Originally Posted by cuddieheadrigg

If the aircraft lost thrust it will descend rapidly even if full control is available elsewhere.

It won't descent more rapidly than usual as most of the time engines are kept to idle for normal operation descents.

Originally Posted by Svarin

I leave to your imagination why such an action would be taken. I have my own idea. And remember, the humans in the cockpit are not the only ones with access to flight controls. The aircraft itself usually has the final say over these controls.

Would you futher elaborate ... ?

[Mr Optimistic]

The point I was trying to make (or be corrected on) is does it seem plausible that the a/c went from A to B without the need to deviate off course to make the sums work. Since the opinion seems to be that the engines were producing thrust, that the a/c remained structurally intact and that a turning manoeuvre would be avoided in the circumstances, was hoping to establish that such was possible without 'hand of God' stuff.

On another point, is it confirmed on the 'WRG: WRN' definition ? 'Wiring' seems and odd way to express a connectivity fault which could be a connector or board coming away from a backplane.

[Lonewolf_50]

Finally, it should be said that a stall is a temporarily uncontrolled, but usually recoverable condition, provided the pilot recognizes it and takes the right actions. The stall is identified by buffet of increasing intensity, usually becoming so intense that, in regulatory language, it is an effective deterrent to further reduction of speed or increase of load factor.

For Hazelnuts:

You raise a couple of questions:

1) Could stall buffet be mistaken for turbulence associated with a CB? If so, how long would it take an aircrew to realize "Hey, this is a stall, not heavy turbulence" and begin to initiate corrective action?

2) What if, worst case, crew is riding/fighting buffet for quite a while ("Blast it, we are in the storm, it's really rough!") not realizing they are stalled ... due to A/S input being unreliable ... you then arrive at an altitude where the A/S input (pitot tubes no longer iced?????) gets sorted out and crew need X seconds to recognize "Hey, that ain't turbulence, we are stalled!" and get on with corrective action ... (this recalls to mind a post over a year ago about stall training, not sure who posted it)

All things combined, the conclusion could be that it is not likely that the airplane stalled at 2:10, and remained stalled all the way down to the surface.

OK, with that in mind, and the above as a possible way events play out, a stalled A330 typically falls at what rate? What you suggest is that with a high rate of descent, instrument conditions, and a crew playing catch up to a stalled heavy, by the time of stall recovery, Rate of Descent and altitude at time of recovery were insufficient to avoid water impact ... or,

crew had to do a recovery from unusual attitude as well as stall recovery, so by the time they were able to recover, get level, and try to arrest rate of descent ... water impact occurred.

Is that what you had in mind when you suggested that the aircraft did not remain stalled all the way down to the surface?

EDIT: I went back and finally found your post in the other thread, where you commented on "Flying the Big Jets" and the vertical velocity figures of 9,000 to 14,000 fpm for a stalled heavy.

[HazelNuts39]

Originally Posted by ASC12

... it isn't surprising at all for an airplane with unreliable airspeed information in rather rough weather to reach a critical AOA.

Not surprising perhaps, but 'maintain pitch and power' is designed to avoid that, and usually does.

[BJ-ENG]

Forward motion

Originally Posted by AZR
Low forward speed is my interpretation

Agreed, and not unreasonable too, but not a fact,
regards,
HN39

In the second BEA report under the section on pathology, there is a statement that forty-three of the victims, spread between business class and the rear of the aircraft, had fractures to the spinal column, the thorax and the pelvis. Pelvic fracture is one of the classifications used by accident investigation pathologists (Naval Flight Injury Manual) to correlate the most serious injury sustained against deceleration and corresponds to a deceleration force in the range 100G to 200G. Interestingly, although thoracic injuries are mentioned, there is no mention of any facial or head injuries, normally associated with forward motion impacts, nor any reports of limb fractures - thoracic injuries are often attributed to forward collision, but could also be explained as a result of contact with seat arm rests during a vertical descent. Of course, the absence of any mention of head or facial injuries may be because the BEA just wanted to present the most significant injuries, or simply that they are refraining from a more detailed description until the final report. The alternative is that there were none, and the forward velocity was minimal.

[asc12]

Originally Posted by HazelNuts39

Not surprising perhaps, but 'maintain pitch and power' is designed to avoid that, and usually does.

Regards,
HN39

In clear air, with visual references (including your PFD), I think so too.

At night, in or surrounded by turbulent CBs, it seems less straightforward and I imagine you could exceed your critical alpha. I still don't see how they get from stall onset to the bottom of the ocean, within spitting lateral distance of where they were in the flight levels, while impacting pancake-like (as opposed to some sort of dive). But that a stall occurred at some point does seem likely--at least plausible-- to me.

[Lonewolf_50]

asc12: a thought on stall and directional control, if we go forwrad on the assumption that at some point aircraft was stalled.

When stalled in turbulent air, is there not the risk of asymmetric lift on the wings inducing a rolling moment? Once such a roll is begun, how does one stop it until the control surfaces are once again effective? (On some aircraft, maybe rudder opposite direction of roll, but that's type dependent, and may be limited to small/light aircraft).

This leads me to the attitude gyros (which feed the PFD) used in the A330: if your aircraft is not designed as an aerobatic machine, would you install a 3D gyro?

I ask because I flew a trainer that we used for VFR spin training and VFR aerobatics training. The attitude gyro typically tumbled, during spins and aerobatic flight, unlike the gyros in high performance jets that allowed "on instrument scan" aerobatic maneuvers (like a barrel roll) with no degradation to the gyro's ability to provide reliable attitude reference.

I have no idea how much 3-axis disturbance it would take to cause such havoc in the A330's attitude reference system, but if such disturbance occurred, that's one more difficult flying task to undertake, recovering from a 3 axis upset using a partial panel scan, that even when one is prepared can be difficult.

I don't envy the BEA and the various search parties their search problem before much was found, since establishing datum rested on assumption, rather than facts, regarding track over ground.

[Chris Scott]

Quote from HN39:
All things combined, the conclusion could be that it is not likely that the airplane stalled at 2:10, and remained stalled all the way down to the surface.

Agreed. Perhaps I can chip-in to offer a few related observations I've been chewing over for a while, at risk of re-stating the obvious (or needing correction).

Prior to 0210z
(a) A/THR was supposed to be controlling speed, and may even have been used by the PF to slow the A/C to turbulence speed. Partial (subtle) loss of thrust seems unlikely, though not impossible.
(b) Alpha-Floor was available, looking at alpha (not speed), and its intervention would have generated warnings.
(c) AP was controlling the selected pressure-altitude: probably still FL350.

Between 02:10:00 and 02:10:59 (selected events – sequence unclear)
(1) Inconsistencies may be apparent on individual ASIs or between the 3 ASIs (although the relevant failure message later transmitted by ACARS would not have been displayed to the crew).
(2) Duty AP disconnects: either due to a system failure or a sidestick forced off-centre.
(3) A/THR disconnects: either due to a system falure or PF closing the throttle levers. If the former, Thrust-Lock would have maintained the N1 at time of disconnect.
(4) Flight controls degrade to Alternate Law (thought to be be ALTN 2). On both pilots' PFDs, therefore, speed protection bands and indices re-configure on ASIs, and "Speed Lim" flags appear; bank-angle protection marks on attitude indicators change to amber Xs.
(5) Alpha-Floor protection is lost (meaning the crew would have to order TOGA thrust for any stall recovery).

I think most of us believe that an upset sequence started between 0210z and 0211z, or very soon after: perhaps while the crew started to realise that they had no reliable speed indication, and were attempting to establish a thrust/pitch regime; perhaps due to severe vertical windshear during this change of modus-operandi. As I think HN39 has stated, the aeroplane would have taken a long time to slow down to the stall.

Prior to 0210z, it seems unlikely the speed would have fallen seriously except in the event that the crew were not monitoring AND all 3 pitot-heads iced-up in concert to produce false, but similar, over-readings. The latter seems implausible.

To sum up: it seems unlikely that the initial upset involved a stall.

Chris

[sensor_validation]

Not mentioned for a while - but if initial problem was caused by icing - what about the effect of ice crystals on the engines, did they somehow "roll back" meaning level flight with "pitch and power" not an option? This phenomena still subject to research

Flights To Gather Data On Jet-Engine Core Icing | AVIATION WEEK

[HazelNuts39]

Lonewolf_50;

The purpose of my post was to dispel a few popular misperceptions about stalling. As to what did happen, I adopt PJ2's wise words that we simply have to wait for CVR and DFDR to tell us.

As to your first question: "Could stall buffet be mistaken for turbulence associated with a CB?", the stall buffet is preceded (in alternate law) by stall warning, a synthesized voice calling "STALL, STALL, STALL" that continues until the AoA is reduced below that at which it starts. I have no personal experience with stall buffet, but believe that it is unmistakably different from "turbulence associated with a CB". I am aware that the training syllabus of airline pilots does not expose them to anything beyond stall warning (simulators are not representative in that regime), but would expect that an experienced pilot is familiar with the turbulence encountered in CB's.

I do not have the quantitative data that you ask for in the remainder of your post. Some very rough estimates have been made many pages back in this thread.

[asc12]

Originally Posted by Chris Scott

Quote from HN39:

Prior to 0210z
1) The A/THR was supposed to be controlling speed, and may even have been used by the PF to slow the A/C to turbulence speed. Partial (subtle) loss of thrust (as-per BA038) seems unlikely so early in the flight.
2) Alpha-Floor was available, looking at alpha (not speed), and it's intervention would have generated warnings.
3) AP was controlling the selected pressure-altitude: probably still FL350.

Between 02:10:00 and 02:10:59 (selected events – sequence unclear)
1) Inconsistencies may be apparent on or between the 3 ASIs.
2) Duty AP disconnects: either due to a system failure or a sidestick forced off-centre.
3) A/THR disconnects: either due to a system falure or PF closing the throttle levers.
4) Flight controls degrade to Alternate Law (thought to be be ALTN 2). On both pilots' PFDs, therefore, speed protection bands and indeces re-configure on ASIs, and "Speed Lim" flags appear; bank-angle protection marks disappear from attitude indicators.
5) Alpha-Floor protection is lost.

Chris

I'm with you in the camp that agrees that the poop really left its pile (as you say, "the upset sequence started") at or after 0210. None of the available alternatives make sense-- really, including a stall. It's obviously shocking enough to all of us to have inspired this much discussion.

I guess I have always thought of severe turbulence as being the physical force instigating the upset, with recovery complicated by unreliable or unavailable airspeed information. With autothrottle set at turbulence penetration speed (or Mach?) the commanded thrust varying all over the place to cope with gusts, lateral shear, and vertical shear-- this seems like a phenomenally bad time to have to very suddenly "pitch and power" fly the plane... especially with temperature shears in my assumed CB affecting recorded Mach. But then it's hard to figure out how the plane got from penetration speed to stall speed (or even within, say, 50kts of stall speed) so fast.

I suppose I settle meekly back in to the "wait for the recorders" group. It's like we got every 10th page of a 100 page mystery.

[Lonewolf_50]

Lonewolf_50;

The purpose of my post was to dispel a few popular misperceptions about stalling. As to what did happen, I adopt PJ2's wise words that we simply have to wait for CVR and DFDR to tell us.

*tips cap*

As to your first question: "Could stall buffet be mistaken for turbulence associated with a CB?", the stall buffet is preceded (in alternate law) by stall warning, a synthesized voice calling "STALL, STALL, STALL" that continues until the AoA is reduced below that at which it starts.

Understood. If AoA detection/measurement is compromised (as it appears airspeed was was compromised) ... I'd need to understand the AoA system in the A330 before asking further questions on that. I'll see if I can find something on that.

I have no personal experience with stall buffet, but believe that it is unmistakably different from "turbulence associated with a CB".

My experience with stalls is from small aircraft, not heavies. Even when dealing with accelerated stall (happened twice, me not at controls) it does feel different from moderate clear air turbulence ... and as I avoided CB/thunderstorms like the plague, I've no "feel" for how that feels. Thunderstorm penetration wasn't an option.

I am aware that the training syllabus of airline pilots does not expose them to anything beyond stall warning (simulators are not representative in that regime), but would expect that an experienced pilot is familiar with the turbulence encountered in CB's.

Roger.

I do not have the quantitative data that you ask for in the remainder of your post. Some very rough estimates have been made many pages back in this thread.

As above, I went back to an older thread where you cited "Flying the big jets" and am happy with the "9000-14000 fpm RoD" for a heavy. It at least puts a boundary on my question, which is good enough.

Thanks.

[mm43]

Originally posted by Chris Scott ...
To sum up: it seems unlikely that the initial upset involved a stall.

You gave a list of events that may have been contributory to what actually happened from 0210 and onwards. A caution regarding the A/P and A/THR; an ACARS warning is not generated each time they suffer a manual disconnection. The warning is due to an automatic disconnection due to their operating parameters having been exceeded. There is one non F/Ctl warning timestamped at 0210, i.e. FCPC2 (2CE) WRG: ADIRU 1 BUS ADR1-2 TO FCPC2,HARD which is a systems warning, but we also have PROBE-PITOT 1X2 / 2X3 / 1X3 (9DA),HARD. What came first, the chicken or the egg??

Depending on how you interpret what could have caused what, the outcome could be completely different in each case.

[henra]

Originally Posted by HazelNuts39

One way to stall an airplane is to gradually reduce airspeed at approximately 1g. The speed at which the airplane then stalls is called the 1g-stall speed, or Vs1g. In the conditions of AF447, such deceleration would take of the order of 1.5 - 2 minutes.

During which time the Aircraft would travel a distance of roughly 10 - 15nm i.e. way beyond where it is supposed to have been found now.

On the other hand this would leave roughly 2,5 - 3 minutes for the descent to the sea which sounds quite plausible for a fully stalled A330 at cruise weight.

Finally, it should be said that a stall is a temporarily uncontrolled, but usually recoverable condition, provided the pilot recognizes it and takes the right actions. The stall is identified by buffet of increasing intensity, usually becoming so intense that, in regulatory language, it is an effective deterrent to further reduction of speed or increase of load factor. To 'unstall' the airplane, the AoA must be reduced below that at which it stalls.

That is the mysterious part about it: why would they let it get into a fully developped stall. In an Aircraft of the momentum and mass of the A330 going from normal flight via incipeint stall to fully developped stall is unlikely to happen in a fracture of a second.
At least in straight and level flight this process takes time.
And leaves time to react.
(we are not talking about a Cessna here)

All things combined, the conclusion could be that it is not likely that the airplane stalled at 2:10, and remained stalled all the way down to the surface.

I strongly tend to agree.
Given the fact that it took overall 5 minutes and brought the plane effectively ~6nm down and ~5nm forward from LKP, I strongly tend to agree.
In a straight line this amounts to ~8nm in 5 mins which equates to net ~100kts if it were to go down in a straight line starting at 2:10 at LKP.
Impossible in an airliner where both min horizontal (~350kts at 35k going down to ~200kts at S/L) and min vertical speed (~200kts at 35k going down to ~140kts at S/L) alone are much higher. This simplification even ignores the fact that it started probably at ~450kts at LKP, so the net average speed towards the end would have to be even lower.

My conclusion: The way down must have been significantly more complex.
A multi stall scenario seems more likely.

I still see the possibility of certain decelleration following the loss of Airspeed Information followed by an accelerated stall e.g. due to vertical gusts leading to a massive wing drop as a potential entry scenario into the disaster.

[HazelNuts39]

Lonewolf_50;

I believe pre-stall buffet at high altitude is (at least in part) a cyclic phenomenon. The airflow becomes locally supersonic in the 'peaky' part of the pressure distribution on the upper surface of the wing, shock waves form, causing (local) separation of the boundary layer, that changes the pressure distribution, causing the shock wave to move , and so on.

[henra]

Originally Posted by Lonewolf_50

As above, I went back to an older thread where you cited "Flying the big jets" and am happy with the "9000-14000 fpm RoD" for a heavy. It at least puts a boundary on my question, which is good enough.

For my taste these figures seem a tad too low for an A330 @210t.

Light GA Aircraft usually spin at a vertical rate constantly surprisingly close to 6000ft/min. You can see that in most accident reports of NTSB where a light GA Aircraft spun to the ground.

Wing loading of these tends to be around 100kg/sqm.
Drag rises roughly to the square of the speed.
so 4 times the wing loading should give very roughly twice the RoD. Looking at the TU154 we find that it had a wing loading of ~400 kg/sqm. RoD prior to impact given by the accident report was ~12000 ft/min. So exactly as could be expected.
In our given case the A330 had a wing loading of ~580 kg/sqm. That would result in ~14500 ft/min at S/L and ~20000 ft/min at altitude.

[robertbartsch]

CNN: Missing tail section found

Tail of Air France jet found in Atlantic - CNN.com