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AF 447 Thread No. 7

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AF 447 Thread No. 7

Old 23rd Mar 2012, 22:54
  #941 (permalink)  
 
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MACH:

You're looking at the glass half-full, which it is not, and pulling those numbers out of your glass.

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Old 23rd Mar 2012, 23:37
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I know it is not relevant to the discussion simply because the airplane is as it is, but if it had been a normal control column everyone would have seen the PF holding the stick right back in his lap, and nobody would have needed any flight instruments to see how very wrong that was.

No pilot would have tried to fly that way in the first place, and I would say that the design of the side stick lends itself to being misused in that manner.

What has/is being done to prevent a reoccurrence?

I have an aversion to robot airplanes and auto flight systems I guess. I will use an autopilot and am happy to do an auto land, but if I ever got to the stage where I could not do everything the autopilot could do, I would give up flying. Many of the pilots I fly with have never learned how to really fly an airplane, which is a pity and is a threat to the overall safety of aviation, and not just airline aviation.

This accident, I fear, will be repeated. And two B757 accidents with a loss of control by the pilot show that it is not an Airbus/Boeing, control column/sidestick problem but a problem with flying skills.
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Old 23rd Mar 2012, 23:46
  #943 (permalink)  
 
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Originally Posted by OK465
....and pulling those numbers out of your glass.
Well of course I am! Are there any more reliable numbers in FCOM?

Just think about how much altitude your Super Sabre would take to recover if you stalled it but did not depart it under similar angle of descent and depth of stall figures.
I'll consider what my F-9, F-4 or A-4 would have done.

If you do not mess it up you would do surprisingly well. If you bobble it a bit, you could use up the whole sky. Now extend the results to a massive aircraft of rather high wing loading, low maximum g capability, and an overprotective flight control system.

The key determinants to altitude lost in recovery are smoothly breaking the stall without secondary stalls, promptly achieving Alpha Max, holding that AOA accurately while accelerating as quickly as you can to just short of the speed that g limiting commences and then not exceeding that speed until level.

Isn't that what they taught you in the AF?
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Old 23rd Mar 2012, 23:55
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Originally Posted by Machinbird
One of our aircraft performance guys can probably come up with some realistic numbers, but I have just described the basic tactical approach to the maneuver.
I may be able to do that, but first I have to explain that I don't necessarily agree with your proposed approach. I agree that you accelerate rapidly when you reduce the AoA to zero lift (or nearly), but that is not optimal if you're trying to recover with minimum height loss, and will also lead to high speed and "g". Intuitively I would expect that the minimum height loss, speed excursion and "g" is achieved by using all the lift that you can get without stalling. A more practical optimum would be the maximum lift available without stall warning, as illustrated by this phugoid:

The AoA of 7 degrees was chosen to stay out of stall warning until at the bottom of the pull-up (the threshold is 10.8 at M.28, and 7.6 at M.53). An even better trajectory would be achieved if the pilot managed to stay on the threshold of stall warning:
Initial normal acceleration 0.73 g, and level off at FL 69, M.47, 276 kCAS, AoA 8.5, and az=2,05 g.

The maneuver assumes constant total energy (thrust = drag), and begins after the airplane has been pitched down to unstall.

The fact that load factor protection is available in ALT2 is a bonus.
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Old 24th Mar 2012, 00:07
  #945 (permalink)  
 
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boofhead

Respectfully, sir, I disagree. Now that we all know where to look, the SS/Yoke kerfuffel is moot. If 447 had not been bobbing like a hula girl and had reasonable stability in the flightdeck, the RHSS might have tipped PF's "hand". The SS cannot be condemned, conclusively, here. Machinbird has shown how uncomfortable the footing/seating was on her Flight Deck. Restraints were not to spec. (from a user standpoint), and the Captain was holding onto the two seats like a sailor holds on to the bar, at 2 o'clock.

Just a thought.
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Old 24th Mar 2012, 03:51
  #946 (permalink)  
 
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And Presto! we have some numbers and they show that,
"If you do not mess it up you would do surprisingly well."
Thank you HazelNuts.

The point about unloading relates to rapidly accelerating away from the zone where it is very easy to achieve secondary stalls. Once the stall is broken, the aircraft will accelerate rapidly, but if a human applies the g too rapidly in his haste to pull up, a secondary stall can result and snatch defeat from the jaws of victory.

Laying on g (in Alt2 law) without an AOA indicator while the airspeed is changing rapidly is tricky.

Just remember that HN39's chart has the following initial condition:
The maneuver assumes constant total energy (thrust = drag), and begins after the airplane has been pitched down to unstall.
We still have to consider how much altitude might be lost in pitching the aircraft down.
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Old 24th Mar 2012, 09:26
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We still have to consider how much altitude might be lost in pitching the aircraft down.
It hasn't been tested and therefore, in the absence of reliable data, it's really anybody's guess. In the TAROM A-310 incident at Orly the airplane pitched down at (more than) 5/s, so perhaps 1100 ft (30 in 6 seconds at 11000 fpm) might be a reasonable guess?

Last edited by HazelNuts39; 24th Mar 2012 at 09:48. Reason: wording
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Old 24th Mar 2012, 16:09
  #948 (permalink)  
 
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We still have to consider how much altitude might be lost in pitching the aircraft down.
As stated by someone way back in these discussions, I would venture that as you vary the CG across the allowable range you will see a significant variation in the response time to generate a pitch rate from 40+ AOA, and thence in the subsequent resulting altitude loss.

(Mach: the only aircraft I flew in my short, undistinguished AF career was a jet that I intentionally spun on a regular basis. I flew others with the militia and was very cognizant of the handling quirks of the 100, 105, F-4 & F-16. However, the A-7 I also departed on a regular basis, thanks to training initially provided by the USN.

The one thing I remember learning from the AF was to keep my hair neatly trimmed. )
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Old 24th Mar 2012, 19:17
  #949 (permalink)  
 
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We still have to consider how much altitude might be lost in pitching the aircraft down.
Originally Posted by 3rd BEA Interim report
The recordings stopped at 2 h 14 min 28 . The last recorded values were a vertical speed of -10,912 ft/min, a ground speed of 107 kt, pitch attitude of 16.2 degrees nose-up, roll angle of 5.3 degrees left and a magnetic heading of 270 degrees.
My experience in the A-4 Skyhawk which had a similar THS configuration to the A330, and the results of the Perpignan A320 accident lead me to believe that the THS trim is going to pace the recovery.

If that assumption is correct, then I'm guessing 20 seconds minimum of nose down stick would be required to recover to flying AOA, (based somewhat on how long it took to trim nose up). As the aircraft begins to nose down, the descent rate will increase to perhaps 15,000 fpm and the IAS will begin to increase. If those assumptions are correct, then you will use about 5000 feet in pitching the aircraft down.

With ~4400 feet to then pull out, that would seem to indicate that 10,000 feet is about the last point one could hope to begin recovery. But there are some BIG assumptions in there.

I did the ~250', zero airspeed, straight down data point once in a Luscombe, and I don't intend to repeat that experiment. I had 5' reserve altitude on completion.
The big question on the pullout was, "am I achieving all possible performance? " The consequences of exceeding the performance limits were rather stark. Fortunately, I felt the burble over the ailerons that told me there was no more performance available.

My big question that day would apply equally to AF447's potential stall recovery since they did not have AOA indicators.
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Old 24th Mar 2012, 20:59
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Learning alot I am. STALL recovery, SIM replication, Douglas Aircraft, etc.

STALL recovery from UPSET at high altitude was not in the Syllabus, and will not be. A back up Speed scale was U/A, it was merely an OPTION. Angle of attack indicators, or even a back up Horizon? The a/c was not equipped to prevent STALL entry, or recovery, but the Pilots must be? How's that?

How many faeries can dance on a pin? I fear that this discussion will lead some to think that flight test will soon include STALL. It won't.

That this a/c behaved surprisingly "well" whilst on its unplanned descent into the sea is beneficial to, whom?

The evidence points to an early LOC, one related directly to the lack of equipment that may have prevented the STALL. If the reliance to prove the PF solely responsible, how is it the PNF hadn't any solutions other than to call the Captain back from rest? The loss of reliable displays were reported to the Captain when he entered, how was he to help?

"Here, Here, and Here, we climb, so go down" Eh? Pitch? V/S? A/S? There was no agreement from the outset, and this is entirely due poor CVR? How so? The PITCH numbers are from the DFDR, No? Where do DFDR data display to the pilots? One cannot fly the Bus by feel, the stick does not communicate "feel". Every response PF made to ROLL shows a chronic bias right by the a/c. What was wrong? If he was synching inputs via screen, were the displays correct?

Who would know, his PITCH prompts went unseen, else the PNF would have not felt the need to cue him to descend.

Three clear graphics show the a/c, its responses, and Pilot talk. Very helpful. The third and last one stops just as Captain enters. No more graphics, sorry. Just getting interesting, eh BEA?
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Old 25th Mar 2012, 06:01
  #951 (permalink)  
 
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A Korean MD11 out of Shanghai was pitched down some 20 degrees after takeoff when passing 2000 feet or so, and could not recover from the resulting dive.


And, Lyman, surely the reason the airplane was flying in such an unstable manner was precisely because it was being held deeply in a stall. Seeing the other pilot holding the control column back in his guts despite the shaking and pitching would have directly prompted any pilot that the airplane was stalled and that the control column should have been pushed forward, no matter what was indicated on the gauges. Without such an obvious clue, it was left to the pilots to interpret what they were seeing, and that was very confusing, to say the least.

However, as I said previously, two sets of crews on the B757 had similar indications of stall and did not respond to it, so nothing is guaranteed. I almost stalled a B737 at 35,000 feet and was amazed at the altitude loss I had to endure before I could get out of the stick shaker regime, even with full power applied. If it had happened at night and with most of my instruments under suspicion I might not have managed to recover either.

Aviation can be very humbling.
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Old 25th Mar 2012, 14:27
  #952 (permalink)  
 
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boofhead

Thanks for your kind and honest response. Aircraft are designed for varying roles, but all must adhere to best practice. I agree that after 109 years, the yoke is "best practice". Other than to merely be "different" I cannot state honestly what possessed the designers of Bus products to hide the SS one from the other.

Keep the joystick, no harm, ( wouldn't it be better between the knees?) but as you say, even with a yoke on the belly button, a/c still STALL. It happens generally because the second pilot is in a tight spot, politically, or he lacks self confidence. Early on, if one of my instructors had started a climb at low altitude, and held back wheel during the WARN HORN, I would not have intervened. "He knows something I don't". We may have crashed, and this happens yet.

It isn't the only problem that did in 447, but there remain more than a few puzzled by the "logic" of hiding life itself from the second pilot. That is quite literally placing your life in another's "Hand", blindly.

Thanks
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Old 25th Mar 2012, 16:41
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Aviation can be very humbling.
Ain't that the truth!
Just for purposes of convenient reference, I am going to bring Hazelnut's Phugoid chart over to discuss how to possibly improve the results. To improve the results, we have to play with the assumptions.
Now lets look at piece of a Wikki article on BFM. The whole article can be found here: Basic fighter maneuvers - Wikipedia, the free encyclopedia
Both turn rate, (degrees per second), and turn radius, (diameter of the turn), increase with speed, until the "corner speed" is reached. At this point, the growing turn radius begins to decrease the turn rate, so the aircraft will reach its best turn performance at its particular corner speed. The corner speed of an aircraft is the minimum speed at which it can sustain the maximum g-force load, and varies with its structural design, weight, and thrust capabilities.[10] It often falls in the area of 250 to 400 knots.[9]

One of the key assumptions in the chart is constant TE=total energy. Suppose we begin accelerating the engines from idle at T=0. (You probably will want to have the engines near idle to break the stall and negate the pitch up moment they would otherwise create.) By T=6 and later, you can begin to strongly increase CAS (Brownish line) and this will increase G available (Lift/Weight-The blue line). In the chart example. AOA is limited (somehow) to 7 degrees by the pilot. Using these conditions, we hit maximum structural g of 2.5 at the bottom of the pullout (321 knots). 321 knots is therefore our cornering speed.

But if we use the engines to strongly accelerate earlier, we have now created a problem. We are now hitting 321 knots much sooner. G limiting then keeps us from continuing to increase the turn rate and if we further accelerate, our turn radius increase will actually slow the turn rate.

Somehow, we have to avoid running through 321 knots. What tools do we have? Pulling the engines back would be one thing of course. What else might slow us? How about induced drag? We can continue to increase wing performance up to alpha max (and with it-Induced Drag). Finally, we have speed brakes available if we need them, but with wing mounted speed brakes, we may lose some of our wing lift performance (CL).

Originally Posted by HN39
An even better trajectory would be achieved if the pilot managed to stay on the threshold of stall warning:
Initial normal acceleration 0.73 g, and level off at FL 69, M.47, 276 kCAS, AoA 8.5, and az=2,05 g.
Using these parameters, we do not get into g limiting at all, so we are probably still leaving the thrust card on the table. (But you will still need some thrust to counteract induced drag and meet the TE=Constant condition).

The practical piloting problem during pullout is this: We do not have real AOA protection in Alt2 Law. We do not have a ready AOA indication. We do have a stall warning system, but it is either on or off-very hard to control AOA like that. Our flight control system is continually trimming off stick force, so a constant stick position causes an increasing AOA demand. There is significant risk of overpulling the stick and getting into a secondary stall-delaying the recovery still further.

You have to be very conservative in your approach to the pullout, particularly where g available is less than 1 g. But that early turn also gives you the most benefit because the turn radius is so small. This is a daunting problem for both pilots and aircraft performance engineers. All you can do is understand what your options are and know your corner speeds.
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Old 25th Mar 2012, 17:44
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It will "BFM" better with the slats out.
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Old 25th Mar 2012, 18:01
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There are hints that Bonin did deploy slats, and Flaps, as well. Doesn't thrust increase cornering speed without increasing speed? (Pull a tighter turn?) Doesn't drag replace Thrust in critical manouvering? So with maximum thrust and maximum drag (nibbling at the STALL), don't we have a relatively stable albeit somewhat ballistic a/c?

One thing that interests me is how Bonin's chronic pull can be explained. One way is to assume that the a/c was not controllable with her nose down. As he lowered her nose, she would want to drop it on her own, (completely, and quickly) and this is what he feared (overspeed), at least theoretically. So he was avoiding the Nose droping through, and maintaining "control". Was he cornered behind the curve?
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Old 25th Mar 2012, 18:58
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Snoop TEN THOUSAND FEET ...

Originally Posted by Machinbird
In the AF447 case, they could have recovered if they had initiated somewhere around 10,000 feet, maybe even less,

Originally Posted by OK465
the only aircraft I flew in my short, undistinguished AF career was a jet that I intentionally spun on a regular basis. I flew others with the militia and was very cognizant of the handling quirks of the 100, 105, F-4 & F-16. However, the A-7 I also departed on a regular basis, thanks to training initially provided by the USN.

The one thing I remember learning from the AF was to keep my hair neatly trimmed. )

IT IS SAID AND WRITTEN : 10 000 FT ! Thank you USN ! Thank you Maching Bird, Thank you OK456 ! Shame to european "aviation".
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Old 25th Mar 2012, 19:15
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RH:

I personally have great admiration for European aviation or any professionally oriented aviation system.

I, myself, have never said anything about '10,000 feet' as being necessarily germane and feel one should easily recognize that this type of conjecturing is purely hypothetical.

People associated with aviation, like yourself, enjoy discussing aviation and making their informal personal inputs, which may or may not be ultimately of any value.

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Old 25th Mar 2012, 19:32
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Originally Posted by OK465
informal personal inputs, which may or may not be ultimately of any value.

OK465, I bet !!

dutchroll
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Old 25th Mar 2012, 20:53
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Originally Posted by Machinbird
One of the key assumptions in the chart is constant TE=total energy.
Hmmm, key assumption?? The "on the threshold of stall warning" trajectory with specific excess thrust (T-D)/W = 0.15 results in level off after 15 s (was 18s) at FL76, Mach 0.51, 295 kCAS, az=2,24 g. An A330 is not a fighter.
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Old 25th Mar 2012, 21:49
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@Lyman:

There are hints that Bonin did deploy slats, and Flaps.
Where are those 'HINTS'?
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