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AF447

Old 8th Jul 2009, 08:51
  #3281 (permalink)  
 
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You may get some answers from this very recent incident...

NTSB: Airbus A330 Experienced An 'Airspeed Anomaly' Northwest Flight Crew In Japan Noted Airspeed Fluctuations

The NTSB has released a preliminary
finding in an incident involving a Northwest Airlines Airbus A330
on a flight in Japan last month in which the onboard computers
switched off the aircraft's autopilot possibly due in part to
inconsistent airspeed indications.

The report reads:

NORTHWEST AIRLINES INC
Incident occurred Tuesday, June 23, 2009 in Kagoshima, Japan
Aircraft: AIRBUS A330-323, registration: N805NW
Injuries: 217 Uninjured.

This is preliminary information, subject to change, and may
contain errors. Any errors in this report will be corrected when
the final report has been completed.

On June 23, 2009, at 0303 UTC, an Airbus
330-323, U.S. registration N805NW, operated by Northwest Airlines
as flight 8 from Hong Kong, China, to Tokyo, Japan, experienced an
airspeed anomaly while in cruise flight at FL390 approximately 50
miles southwest of Kagoshima, Japan. The crew reported that they
were in normal cruise at FL390 and in visual conditions with some
convective weather displayed on radar about 25 miles north of
track, with thin cirrus clouds ahead.

After entering the cirrus and moderate precipitation and
turbulence, the crew observed, and FDR confirms, the autopilot and
autothrust switch off, and the aircraft switched to Alternate Law.
The master caution and warning messages were activated. The crew
followed flight manual procedures and the autopilot and normal law
returned in about one minute, however the event quickly repeated
itself, lasting for about 2 minutes. The crew turned the airplane
60 degrees off course to exit the weather as soon as the anomalous
indications were observed. The autopilot, autothrust and other
controls returned to functioning, but the airplane remained in
alternate law for the rest of the flight.


The crew observed, and FDR confirms, large airspeed
fluctuations, small altitude fluctuations, and an overspeed alert.
The flight continued to Tokyo, Narita airport and landed with no
damage or injuries to the 9 crew and 208 passengers on board.

The incident occurred in Japanese airspace, and the
investigation was delegated to NTSB by the Japanese Transportation
Safety Board, who assigned an Accredited Representative to the
investigation.
FMI: National Transportation Safety Board
ITman is offline  
Old 8th Jul 2009, 09:04
  #3282 (permalink)  
 
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> therefore would loose the sycronisation path with the Satellite and loss of ACARS transmission.

While quite possible, not necessarily in this case. The target satellite was effectively directly overhead, and the antenna beam angle is around 60 degrees. So in a flat spin that is horizontal there should only be a few degrees of wobble in the bird position, and that probably wouldn't even be detectable as a gain change.

If the link was lost for other reasons, I suspect that it might be recovered moderately easily since the bird wouldn't be moving much in terms of antenna steering angle.
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Old 8th Jul 2009, 09:48
  #3283 (permalink)  
 
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The link to the satellite might be broken if the a/c was rotating (spinning) The antenna on the a/c might not be able to keep up with the changes in signal polarisation caused by the rotation of the aircraft. Such a vulnerability is dependant on the type of polarisation used. Perhaps JD-EE can advise.
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Old 8th Jul 2009, 10:05
  #3284 (permalink)  
 
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The link to the satellite might be broken if the a/c was rotating (spinning) The antenna on the a/c might not be able to keep up with the changes in signal polarisation caused by the rotation of the aircraft. Such a vulnerability is dependant on the type of polarisation used. Perhaps JD-EE can advise.

Can I just pre-empt JD-EE's response by saying, no the aircraft would have to be spinning several orders of magnitudes faster than is possible to upset the signal ploarization.
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Old 8th Jul 2009, 10:39
  #3285 (permalink)  
 
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barstow, that is right, in part. The communications path and antennas, of course, use circular polarization. So changing orientation cannot upset the polarization. With circular polarization you cannot get cross polarization. The Inmarsat people used that trick to good advantage.

JD-EE
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Old 8th Jul 2009, 10:47
  #3286 (permalink)  
 
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That's another useful data point. I am guessing the point where a loss due to rain becomes feasible to consider is maybe 15,000 feet give or take some.
.. and maybe a very good one, with the limited points available after 02:10
Could also be due to pitch or roll angle if momentarily exceeded those limits discussed above

Another data point that has been lost way back when, to add to the VS (& possibly tailcone) is the single spoiler that was found.

Admittedly a very small and dubious one, but nevertheless, bearing in mind the suggested impact mode, could this really have been broken off (apparently by a forwards force & upwards bending moment) with the assocaited flaps in the retracted position?
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Old 8th Jul 2009, 11:43
  #3287 (permalink)  
 
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When you depart an Aircraft from High Altitude unintentionally,or in an intentional Training Sortie,the Aircraft does NOT enter a flat spin,unless deliberately induced,although it can seem like that from inside the cockpit.It actually loses lift from different points along the wing and stabiliser,so enters a tumble of pitch yaw roll oscillation.If you used to watch "War in the Air" films of battle damaged B17s and B24s entering spins,these are rather more uncontrolled tumbles than actual spins.A flat spin is rather hard to get into especially in a large aeroplane,but a departure tumble can happen ,especially when flying through extreme Up and Downdrafts in Cbs.We used to do that in Training when deliberately exceeding Crit mach to show departure recovery.,albeit many years ago.Incidentally KLM used to use 2 Harvard Trainers up to the 70s or maybe longer to give Long Haul Captains Spin awareness Training,as Crews had not seen the manoevre for so long since initial Flight Training.I believe the Pilots Union had it stopped as it caused much trepidation to older Captains.To experience the like in a 200 Ton Airliner beggars belief.let alone trying to recover with normal controls,let alone a side stick in "Alternate Law"!!!

Last edited by FAStoat; 8th Jul 2009 at 12:31.
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Old 8th Jul 2009, 12:14
  #3288 (permalink)  
 
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Admittedly a very small and dubious one, but nevertheless, bearing in mind the suggested impact mode, could this really have been broken off (apparently by a forwards force & upwards bending moment) with the assocaited flaps in the retracted position?

I asked this question some time ago and got what seemed like a fair answer in that if the tail impacted first, it could have disintegrated leaving the vs free to float away. The only other possibility is that the vs separated in flight at some stage, but does the recovery position in relation to the remainder of material recovered support this view ?.

I just can’t accept that a perfectly serviceable aircraft would break up in mid air unless airframe stress limits were exceeded by (probably) quite a wide margin. The only things remaining, assuming the pilots were not practicing aerobatics, are extreme weather conditions or massive systems failure. The acars evidence, really doesn’t support the latter, looking more like the result of what was happening, rather than the cause.


I don’t take sides re climate change, (too much politics, not enough science) but assume for a moment that climate change is in process and that more severe weather is one of the byproducts. Could it be that what used to be considered extreme weather conditions are now more commonplace and extremes are now more so ?. One snippet of evidence in context that might support this view is the increased incidence of pitot icing and failure in the last few years. Has this always been a problem, the result of changed flying practices, or what ?. Pitot probe design hasn’t changed much in decades, so why are they failing in the same way now ?…
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Old 8th Jul 2009, 12:21
  #3289 (permalink)  
 
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My point was more about thinking through the implications of what little external structure has been found... whether it supports the BEAs view on the state of the a/c and mode of impact... re the spoiler which has been given little attention, undertsandably so perhaps.

The implication for it it to be broken off in the way it appears might be:


The flaps were down given underside access to water impact forces in a rightside up impact
It was out, and that wing sinking rapidly but backwards
The a/c completely tumbled with it out (least likely)
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Old 8th Jul 2009, 12:40
  #3290 (permalink)  
 
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speed-altitude

re: #3245 (Hyperveloce)

Pretty accurate guess Hyperveloce, my CASIO shows 4431 ft

regards,
HN39
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Old 8th Jul 2009, 13:05
  #3291 (permalink)  
 
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Just to review, 3 1/2 other things can possibly replace the sideslip.
1) When close to the critical AOA, dropping an aileron (say in rapid response to the start of roll-off on one side) effectively increases the AOA in the region of the aileron and could stall that region.
2)When close to the critical AOA, having a some upward gust applied to the outer wing section on one side, causing it to exceed critical AOA.
3)When close to the critical AOA, making a smaller radius turn so that the inside wingtip is flying more slowly that the outer wingtip and effectively causing a greater AOA on the inside wingtip (same vertical vector amount, less horizontal). More an issue with long-winged aircraft.

and 1/2) The typical spin entry we're all aware of, when close to the AOA kicking in rudder for some reason. With the A330 you can substitute differential engine thrust for the rudder. While it may or not slip sideways overall, that's not the problem. It's the yawing so that the inside wingtip flies more slowly or even backwards relative to the other tip. Due to vertical vs horizontal flight vectors of the tips, the inside tip goes critical and the other away from critical.
Your first three points are confusing roll with sideslip. Coordinated roll will not invoke a spin by itself, the conversion of aoa to yaw angle with roll off creates the effect. Your first three points explain roll-off.

Your 1/2 point is what is taught in ppl straight wing trainers. While this applies to the A330, it's effect is minor compared to the effect of unsweeping the upwind wing and increasing sweep on the downward wing. This sweep effect due to sideslip is easy to visualize. Draw an A330 planform on paper with a vector coming from 20 degrees off the nose. Tilt the paper till the vector is vertical. Observe that upwind wing gets longer and is unswept. The downwind wing gets shorter with increased sweep.

Also understand that CLmax changes with the cosine of the sweep.

Hope this helps. And thanks for demonstrating that stall and sideslip are the two components needed for spin entry.

Edit: The 1/2 point also explains roll-off. So all 3.5 points don't replace sideslip, but do explain how a roll-off can occur which does induce sideslip once roll-off occurs.

Last edited by ClippedCub; 8th Jul 2009 at 13:22.
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Old 8th Jul 2009, 13:08
  #3292 (permalink)  
 
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Satcom & High Altitude Flight

-for the satcom/ACARS, we would need the real radiation pattern of the antenna (polar nulls ?) and some data about the link budget and the signal modulation/processing to assess whether the weather conditions and/or an unusual attitude of the airframe may have weakened and/or masked the satbeam to a point of disruption. there wasn't any electrical activity detected from satellite imagery, but the flight LH507 which preceded AF 447 by 20 mn was subjected to St Elmo's fires on the left-hand side of the cockpit: possible sources of interferences here, with a band around 1.5 GHz or comms ? (don't think so but I may be wrong). also wonder about the functional temperature range of the antenna.
-for the loss of control at high altitude, I was frightened by the rapidity of the loss of control of the Adams Air plane: the crew attention was focussed on a failed IRU, did the AP disengage and let a slight bank to progress ? (in the Qantas case, when the AP 1st disengage, it allowed a slight altitude drift to unfold). between the banking alarms, the clicket sounds (30s) and the first prayers, it is a matter of 40-50s. (I now hear their prayers from times to times and the horrible aerodynamical noise, how can this be available on the web ? I do not understand).
Jeff
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Old 8th Jul 2009, 13:12
  #3293 (permalink)  
 
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NSTB release

Originally Posted by ITman View Post
You may get some answers from this very recent incident...
NTSB: Airbus A330 Experienced An 'Airspeed Anomaly' Northwest Flight Crew In Japan Noted Airspeed Fluctuations
The NTSB has released a preliminary
finding in an incident involving a Northwest Airlines Airbus A330
on a flight in Japan last month in which the onboard computers
switched off the aircraft's autopilot possibly due in part to
inconsistent airspeed indications.
Interesting, and this one generated an overspeed alarm, not a stall alarm.
But it also seems that the airspeeds were fluctuating, whereas they just dropped in the Air Caraïbe case. Maybe a slightly different failure mode/sequence ?
Jeff
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Old 8th Jul 2009, 13:50
  #3294 (permalink)  
 
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Re impact "with" vertical acceleration

RE: #3248 (FanAviation)

I heartily support your observations except on one (very minor) point.

Quote:
Then it says "the plane has probably (vraisemblablement)) hit the surface of water in flight line ("with" but the word is missing here) a strong vertical acceleration"
/Unquote

In my opinion the word "with" is not missing but was incorrectly inserted in the english translation, and later in the Findings (french and english texts). The 'frenchman with a scientific background' was quite correct. Inserting the word "with" makes the "acceleration" part of the impact entry conditions, which it is not. Without the word "with", the statement correctly observes only that visual examination showed that the parts had been subjected to strong acceleration (caused by impact forces).

regards,
HW39 - newbie dutchman with engineering background
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Old 8th Jul 2009, 14:05
  #3295 (permalink)  
 
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Actually, at equatorial water temperatures, say, 25deg. C and above, in saltwater, a body , if it sinks at all, can surface in less than 24 hours. Depends on exact temp, body fat, clothing, completeness of the remains, salinity. Water temp is the most important factor for 2 reasons. As water warms, at least above 0C, it expands, reducing its density. Also, warmth accelerates decomp and the attendant release of gasses.
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Old 8th Jul 2009, 14:14
  #3296 (permalink)  
 
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NTSB on NW A330:
The crew observed, and FDR confirms, large airspeedfluctuations, small altitude fluctuations, and an overspeed alert.
Here's what the FO wrote in an email the day after:
... Entering the cloud tops we experienced just light to moderate turbulence. (The winds were around 30kts at altitude.) After about 15 sec. we encountered moderate rain. We thought it odd to have rain streaming up the windshield at this altitude and the sound of the plane getting pelted like an aluminum garage door. It got very warm and humid in the cockpit all of a sudden. Five seconds later the Captains, First Officers, and standby airspeed indicators rolled back to 60kts. The auto pilot and auto throttles disengaged. The Master Warning and Master Caution flashed, and the sounds of chirps and clicks letting us know these things were happening.

Jerry, the Capt. hand flew the plane on the shortest vector out of the rain. The airspeed indicators briefly came back but failed again. The failure lasted for THREE minutes. We flew the recommended 83%N1 power setting. When the airspeed indicators came back. we were within 5 knots of our desired speed. Everything returned to normal except for the computer logic controlling the plane. (We were in alternate law for the rest of the flight.)...
GB
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Old 8th Jul 2009, 14:26
  #3297 (permalink)  
 
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My point was more about thinking through the implications of what little external structure has been found... whether it supports the BEAs view on the state of the a/c and mode of impact... re the spoiler which has been given little attention, understandably so perhaps.
Not qualified to comment on the aerodynamics, but you could get a good idea of force vector by looking at the remaining attachment points and or pivots, if you could find a high enough res photo. For example, hole elongation on a hinge point prior to pin shear.

Some of the attachment points looked fairly intact, iirc...
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Old 8th Jul 2009, 14:31
  #3298 (permalink)  
 
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Latest from Eurocockpit

Eurocockpit, which has the inside track from Air France pilots, has just posted their first reaction to the BEA initial report
Eurocockpit - Accueil

For the moment it's only in French. They promise an English version. But their point is that they suspect the BEA and Air France of being economical with the truth.

L'affaire du vol AF447 ne fait que commencer, et nous pouvons dès aujourd'hui annoncer qu'il sera très difficile de cacher la vérité.

Which means.... The case of AF447 has only just begun and we can from today announce that it will be very difficult to hide the truth...

Eurocockpit says that on June 5 -- four days after AF447 -- Air France modified the standing Airbus procedure for handling unreliable airspeed indications. The June 5 note told crews to ignore stall warnings and run the checklist before undertaking corrective action, says Eurocockpit. Perhaps the experts could explain the implications of that.
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Old 8th Jul 2009, 14:43
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Water temperature

The water temperature in the search area was 30°C
If that seems high to you English etc, it was 2° N of the equator, and I am here in southern Brazil, 26°S and 27°C is quite common in summer
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Old 8th Jul 2009, 14:55
  #3300 (permalink)  
 
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Clipped
Hope this helps. And thanks for demonstrating that stall and sideslip are the two components needed for spin entry.
You are confusing side-effects with the essential requirements of spin entry and spins. And since like Dani, you wish to protect and retain your pre-existing mis-understandings I won't require you to change. Since this thread is about AF447 it would be inappropriate to sidetrack and give you flight instruction. I'll let my statement on spin entry stand, it is entirely accurate. Ignore if you wish. Hope that helped.

Last edited by ttcse; 8th Jul 2009 at 15:59.
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