Clandestino

Good for you. Since the topic we are discussing is AF447 accident and not some informative video, did you read BEA's third interim report? The one with DFDR and CVR readouts?
You are claiming that AF447 entered the storm cloud, which is at odds with Nz trace. Would you mind explaining the process that enabled you to heartily disagree with official interim report?

The ice crystals that are main suspect in the AF447 pitot blockage are found near active cells but not within them. Avoiding the radar returns won't keep you clear of the naughty ice.

Organfreak

Thermostat said:
Indeed we should. So, will you share with us the name of this program?
It sounds like the NOVA special (PBS) that came out before Interim Report #3. (Or was it before #2?) Though highly speculative, I thought it was really well done, considering they didn't know what the hell they were talking about!
It didn't posit a horizontal splashdown, even.

mm43

Here is a quote from a declassified U.S. Army Missile Command, Redstone Arsenal, AL, document by Dorathy Stewart dated 27 June 1990 and entitled -

"Occurrence and Detection of Supercooled Water in the Atmosphere"

- with reference to - "Supercooled Water; Aircraft Icing; Clouds; Climatology".
and another;The last sentence of each quote is important, as we are dealing with events that had their beginnings in relatively clean air above an expansive maritime environment.

So it would appear that the military had at their disposal some definitive data on this form of icing over 20 years ago.

HazelNuts39

As BEA puts it on page 30 of Interim Report No.1:
IMHO the heating of the pitots is designed and has been demonstrated to function in any quantity of supercooled liquid water likely to be encountered. The icing detectors would have detected the presence of significant quantities of liquid water.

Clandestino,

For distribution of liquid water and ice particles in convective clouds, read IR#3 page 50.

HazelNuts39

Well, I thought so too, but changed my mind after looking at Owain Glyndwr's data. With Owain's help I did a similar analysis and got similar results shown in the graphs below. The second graph shows how AoA slowly reduces until the airplane is unstalled.

mm43

The BEA's comments are accepted as such, but at the time of making them they hadn't completely ruled out that possibility. I have pointed out that the known science doesn't rule it out either.

In respect of Owain Glyndwr's stall recovery scenario, your follow-up is appreciated. It follows what I had in mind when creating graphics showing the relationship of elevator and THS angles to the relative airflow - some time back. As the pitch is reduced, the applied thrust leads to increasing IAS which rapidly reduces the the AoA and the wing attains the lift to allow the recovery. At the time I had envisaged no more than 10° ND would be required to get the wing flying again, and that appears to have been borne out.

RetiredF4

Would somebody explain, on what facts the following happens in the first 12 seconds of the above graph:

Pitch is reduced from +15° to -10° = 25° change
FPA increases from -22 to -34 = 12° change
AOA decreases from +35 to +22 = 13° change

Speed in this timeframe is not specified, but is esentially important for generating lift. Drag in this AOA regime has an influence as well, where can it be found in the graph?

On what ground would the AOA change (13°) be grater than the FPA change (12°) by changing pitch (25°)?
Wasn´t the initial AOA according BEA higher than 40°?


Out of my own expierience with such a high initial AOA and such low speed the pitchdown initially increases the FPA by the same amount, the pitch is decreased,, giving only a minimal change in AOA and an increase in FPA and descent rate.

The expierience in the A330 sim from PJ2 and another Airbus pilot make me believe, that this magic graphs miss some vital points. Also all accepted procedures for combat jets as well as the new updated stall recovery procedures speak of the need to place the stick forward until the stall warning stops, which would not be the case until 45 seconds into the recovery like shown in the graphs.

HazelNuts39

RetiredF4,

To begin with your last point: If the nose-down pitch rate is maintained until the stall warning stops, that would occur at t=21 seconds and 27 degrees ND pitch. Level flight would be achieved at t=42.5 seconds, FL262, 324 kCAS. I suspect that Owain Glyndwr did not show that scenario in his graph because he found it difficult to imagine that an ATP would deliberately do that in an airliner.

Owain explained the 'Performance Model' in his post #87:
The 'Performance Model' consists of lift, drag and thrust data as functions of relevant parameters, and the trajectory then follows from Flight Mechanics, i.e. Newton's laws. It is driven by the specified variation of pitch attitude versus time. As opinions differ regarding the the achievable rate of pitch change, Owain's graph shows trajectories for pitch rates of 1, 2 and 3 degrees/second. These rates bracket the values observed by PJ2 in the simulator, and the responses of the airplane to elevator movement observed in the DFDR traces of AF447.

"Wasn´t the initial AOA according BEA higher than 40°?" The recorded AoA at 02:11:45 was just about 40°. In my graph I chose to stay with the recorded pitch attitude and calculated flight path angle, which result in AoA=36° for symmetrical flight in still air. The difference between that value and BEA's is attributable to the bank angle of 30° existing at that moment.

RetiredF4

and there are drag-data available for those flown AOA´s, despite the fact, that this area was neither tested nor evaluated?

HazelNuts39

RetiredF4;

The pre- and post-stall aero data have been obtained from analysis of the DFDR data. Within the normal flight envelope these match authentic Airbus data. Outside that envelope the verification consisted of running the model through the recorded time histories of pitch and N1, and comparing the resulting 'model' trajectory (the violet line in Owain's graph) to the actual DFDR trajectory (the yellow/red line).

Machinbird

I'm glad we are bringing up this subject again. Pointing the nose below the horizon adds effective thrust along the aircraft axis in the amount of sine(negative pitch angle) x weight of the aircraft. In effect you are powering out of the stall with sufficient power to let the aircraft accelerate despite the high induced drag.

This probably isn't the most efficient way to get an airliner out of a stall, but for one that does not have an AOA indicator, it has a lot to recommend it in that the likelihood of secondary stall is drastically reduced. You just have to get the nose low enough initially so that you can actually accelerate. Surprisingly, angles of as little as 10-15 degrees nose low seem to be sufficient for the A330 to accelerate, despite having a very high initial AOA.

In the military aircraft I've flown, we were always concerned with departures from controlled flight (spins), thus the importance of unloading the wing promptly before you began to generate unintended rates of yaw/roll.

With an aircraft that is (relatively) stable in the stall, you just have to avoid doing something stupid with the controls.

I hope someone (like NASA) does further study on this method of stall recovery.

HazelNuts39

OK465,
Sorry, I forgot to label the secondary axis. Yes, it is Nzw, the acceleration normal to the flight path in 'g'.

OK465

Thanks. (deleted the post with the question, thinking some more about it.)

Why doesn't Nzw go to 1 at zero FPA?

roulishollandais

Due to not enough test flights, knowledge of A330-200 limits and rate limitations of flight envelope is not sufficient.

Loss of speeds gets a critical situation to the aircraft's system design, reconing and protections. So the system reversed to Alternate 2B Law.

At this time we find a total lack for man-machine interface in terms of effective aircraft observability.

In that moment the restitution of human's classic hand and high altitude skills is not possible due to bad selected, bad teached, undertrained concierge-pilots. Don't forget their questions have been throwes off since 1/4 century by airlines, national and former european civil aviation autority.

That situation means that UAS is first an unsolved SYSTEM problem (despite inertial system exists on the aircraft which may not be clogged by ice ?) which will get a human UAS unsolvable problem,

Recording more and more parameters in the black boxes would be useless at preventing next SUCH accident.

Engineers and pilots have first to coordinate on the ground to elaborate transfer from process to SOPs.

We do not know the total conversation (due to BEA decision) and why1, why2, why3, why4, why5, and how the crew pulled to stall.

But, as they are not teached to, AF pilots could not invent "unloading the wing" technic, nor imagine computed but not displayed AoA, to replace the airframe shape in the airflow to recover.

1. None of the three simulations reported in the thread, and very well compilated by TurbineD, can get accreditation from test pilots, as simulators have not enough information. So no available SOPs can be written on these simulator experiences basis.

2. Owain G. takes only the half of the problem as stall is not a speed problem but an AoA problem :i.e. a free faller diving at 300 km/h falls without lift, only drag, but may deplace himself forwards with felt , strong lift, 40° pitch ND, falling 200 km/h changing only a little his arms positions and Cg position.

The deepstall is another case were you have speed and not enough lift.

3. On the other side, the "unloading the wing" technic, that Machinbird pulled like a magician from his large fight piloting science, is used in 0g certified Airbus flights to train astronauts. An that technic combined with official performance calculations reported by Hazelnuts39 show that THAT TECHNIC , and only that technic, could have been used with AoA and training, to overcome the stall with relieble new SOP.

In conclusion, developing these two points, further AF447 may be avoided.

Owain Glyndwr

Franzl,

Good questions that deserve a reasoned reply. Sorry to have got out of sequence, but domestic duties got in the way.

I assume we are not doubting that stuffing the nose down will eventually give increased EAS and reduced AoA, the debate being the mechanism by which one achieves that end state.

I rationalised it this way:

Suppose we start with pitch +15, Gamma -25, AoA +40 and instantaneously pitch down through 25 deg to -10. (this is a thought experiment so we can do that)

AoA remains at +40 for the moment as you suggest, but that means gamma goes to -50. EAS hasn't changed, neither have CL and Cd at constant AoA so drag and lift are unchanged. However we now have a large additional gravity component so the aircraft will accelerate in absolute terms, i.e.TAS will increase, again as suggested in a later post. But in addition the aircraft is now descending more rapidly into denser air so there is a double effect on EAS, and the thrust is also increasing due to altitude effects which also helps a bit although this is not anything like as important as the gravity effect since the maximum thrust one might get at say FL350 is only about 7%W whereas a 25 deg FPA shift is worth 42%W.

If EAS increases at constant AoA the aircraft will develop an upwards acceleration normal to the flight path and thence an upward velocity component which, with the increased airspeed will result in a reduction in FPA. You can see this in HN39's traces. [It will also of course experience an increase in drag which partially offsets the benefits, but I think this only partially offsets them]

A reduction in FPA, WITH PITCH HELD CONSTANT, will give a reduction in AoA.

Cd is very sensitive to AoA above the stall, so the drag reduces more than the effect of increased EAS and the whole response is "speed unstable" as it were, with an increasing acceleration and reduction in AoA as time goes on until the AoA is reduced to below S/W limits.

That is, I think, the basic recovery mechanism, but in the early seconds the exact response depends on a changing balance between the various effects, and these in turn depend on the exact time history of applied pitch, so it is really quite difficult to answer your questions about the first twelve seconds.

Drag (and lift) in this case were calculated by analysis of the traces extracted from the BEA cartoons, the only assumption needed being how thrust varies with altitude and RPM and there are well established scaling rules for that. The justification for staying with these values is that the actual trajectory can be calculated by inputting just pitch and power, the output being speed and altitude. Hence the purple line on my original graph.


I don't think there is any conflict with your point about holding forward stick until the S/W stops, the only qualification is that I assumed the pilot flew constant pitch.


I don't think PJ2 will be upset if I say that in my conversations with him he confirmed that on at least one occasion he executed a recovery from 30 deg AoA using 10 deg ND pitch - it took about 15000 ft.

Lyman

@Owain Glyndwr
"That is, I think, the basic recovery mechanism, but in the early seconds the exact response depends on a changing balance between the various effects, and these in turn depend on the exact time history of applied pitch, so it is really quite difficult to answer your questions about the first twelve seconds."

In the early seconds of each partial recovery, wasn't the crew presented with a "re-invigorated" STALLWARN?

Having sussed all the napkin calcs presented here, would the PF go immediately to ND? Or would he secure TOGA thrust, and "maintain altitude" with aft stick?

The DFDR tells us little of theoretical benefit to our crew from possibilities that were never entertained at any level of practicality.

Call me a wise ass, but I venture to say the crew was so absorbed in trying to "PREVENT" a STALL, that they spent no time trying to recover from one. Again, the focus is shifted from the problems that caused the crash to hypotheticals re: after the fact suppositions? IMHO.

Owain Glyndwr

If you have read my previous posts you will be aware that I avoid any comment on what pilots might or might not have done - I leave that to more qualified observers.

The DFDR is not intended for the use you imply, but you cannot say that 10 deg ND is a theoretical possibility outside the levl of practicality since they actually went there just after 02:12:45

Lyman

With great respect I am saying that 10 degrees NOSEDOWN was not done for reasons discussed at length, specifically, a proposed fear of Overspeed, and the fact they didn't suss STALL.

I think you misunderstand my DFDR remarks.

At 2:12:45, at 10 degrees NOSE DOWN, were they there due command, or airframe trying on its own to recover from STALL?

Owain Glyndwr

IIRC, as looking at the traces will tell you, at 02:12:45 they were at 10 deg nose down with full up elevator and flight idle power. The aircraft, as I have said before, has no natural nosedown pitch at the stall. It responds to applied elevator and thrust. In this case it seems that reducing thrust to idle or thereabouts produced enough pitch to get to -10 deg.

Lyman

No natural tendency to lower its nose in Stall? Are you sure? I thought that was one of the cues for a Stall suss. Is there something I am missing re: CG?