AF 447 Search to resume
JD-EE;
Going from memory as it was a long time ago...in Canada and I believe the US, if one crew member left the cockpit while the aircraft was cruising at 410, the remaining crew member was required to don his mask. Above 410 one crew member had to wear his mask at all times. Below 410 there was no requirement to wear the mask under normal operations.
Hope this helps.
Going from memory as it was a long time ago...in Canada and I believe the US, if one crew member left the cockpit while the aircraft was cruising at 410, the remaining crew member was required to don his mask. Above 410 one crew member had to wear his mask at all times. Below 410 there was no requirement to wear the mask under normal operations.
Hope this helps.
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Lonewolf 50, your finding the drop rate of a stalled airliner raised a DUH factor in me.
If I remember the BEA report it heavily implied more vertical component than horizontal to the oceanic impact as deduced from damaged elements to which they had access.
We're talking of 100 to 150 MPH fall rate. Therefore the plane was not in anything close to a flying status when it hit. It may have had some forward velocity, but it would have been well below any known stall speed unless surface winds were hurricane force.
If the plane was NOT stalled it's vertical velocity would have had to be on the order of 200MPH to be noticeable as an effect on the wreckage, I suspect.
Sometimes units translations help. It didn't really dawn on me what speeds were likely involved until I made that translation.
I also got to thinking that the plane was making headway on the order of 4 to 5 miles per minute. In a little over 4 minutes it could not be much further from LKP than 10 miles if it also had to traverse the vertical distance as well. The BEA must have been out of its mind to search way out where it invested so much time and money.
If I remember the BEA report it heavily implied more vertical component than horizontal to the oceanic impact as deduced from damaged elements to which they had access.
We're talking of 100 to 150 MPH fall rate. Therefore the plane was not in anything close to a flying status when it hit. It may have had some forward velocity, but it would have been well below any known stall speed unless surface winds were hurricane force.
If the plane was NOT stalled it's vertical velocity would have had to be on the order of 200MPH to be noticeable as an effect on the wreckage, I suspect.
Sometimes units translations help. It didn't really dawn on me what speeds were likely involved until I made that translation.
I also got to thinking that the plane was making headway on the order of 4 to 5 miles per minute. In a little over 4 minutes it could not be much further from LKP than 10 miles if it also had to traverse the vertical distance as well. The BEA must have been out of its mind to search way out where it invested so much time and money.
I much admired Hazlenut's description of stalls. With nearly all training now being done on simulators few airline pilots ever experience genuine stalls, or even the approach to the stall on the types for which they are qualified. I am now retired but used to be a training captain on VC10s (T-tailed), 707s and 747s, and did C of A test flights on all 3 types.
The stalls both in training and on C of A flights were always, wings level, slow deceleration (1kt/sec) to the 1G stall (or stick push in the case of the VC10). I have no experience of stalls in banked flight, or accelerated stalls when pulling G. The aerodynamic buffet in all cases was distinct from the turbulence felt in clear air near jet streams and from the turbulence in the vicinity of thunderstorms.
The 747 was an interesting case since the stall speed clean was defined by the maximum acceptable buffet, D P Davies describes it as a violent vertical bounce, sometimes with a lateral component. To the best of my knowledge the 747 has not been stalled in the clean configuration. In each of the flaps down configurations the stalls were immaculate with good natural buffet, good controllability and a good margin between the buffet and the 1G break, followed by a classic nose drop.
The VC10, being a T-tail aircraft, required a stick shaker and stick pusher, and on C of A flights was always fitted with an incidence meter above the coaming. If the stick push had not occurred before 14deg incidence you pushed like mad!
I relate all this because of the discussion in previous posts about whether the pilots could have distinguished between pre stall buffet and the turbulence associated with thunderstorms. I think the answer is in most cases 'yes', the two are distinguishable. However, in heavy turbulence it is highly probable that the pre stall buffet would be 'lost' in the general ambient turbulence. And in really heavy turbulence one's brains feel rather 'scrambled' which would make it even more difficult! In which case it is quite possible that the pilots on AF447 would not have been able to discern the pre stall buffet.
The stalls both in training and on C of A flights were always, wings level, slow deceleration (1kt/sec) to the 1G stall (or stick push in the case of the VC10). I have no experience of stalls in banked flight, or accelerated stalls when pulling G. The aerodynamic buffet in all cases was distinct from the turbulence felt in clear air near jet streams and from the turbulence in the vicinity of thunderstorms.
The 747 was an interesting case since the stall speed clean was defined by the maximum acceptable buffet, D P Davies describes it as a violent vertical bounce, sometimes with a lateral component. To the best of my knowledge the 747 has not been stalled in the clean configuration. In each of the flaps down configurations the stalls were immaculate with good natural buffet, good controllability and a good margin between the buffet and the 1G break, followed by a classic nose drop.
The VC10, being a T-tail aircraft, required a stick shaker and stick pusher, and on C of A flights was always fitted with an incidence meter above the coaming. If the stick push had not occurred before 14deg incidence you pushed like mad!
I relate all this because of the discussion in previous posts about whether the pilots could have distinguished between pre stall buffet and the turbulence associated with thunderstorms. I think the answer is in most cases 'yes', the two are distinguishable. However, in heavy turbulence it is highly probable that the pre stall buffet would be 'lost' in the general ambient turbulence. And in really heavy turbulence one's brains feel rather 'scrambled' which would make it even more difficult! In which case it is quite possible that the pilots on AF447 would not have been able to discern the pre stall buffet.
Bergerie1, thank you for an enlightening contribution. I haven't stalled a transport category aircraft but have done so in a D - level simulator which is required to replicate the behaviour of the aircraft (in a stall) as part of its certification.
During discussions, stall and high speed buffet came up. I would be interested in hearing if you believe it is possible to differentiate between high speed buffet and low speed buffet at cruise altitude. The question came up as the enquiry into "coffin corner" arose, (in the analysis it was determined that the aircraft was a long way from either boundary).
During discussions, stall and high speed buffet came up. I would be interested in hearing if you believe it is possible to differentiate between high speed buffet and low speed buffet at cruise altitude. The question came up as the enquiry into "coffin corner" arose, (in the analysis it was determined that the aircraft was a long way from either boundary).
PJ2
I have only once been to the aerodynamic ceiling and that was on a VC10. I was young co-pilot at the time and the training captain took it up to 46,000ft. Where he demonstrated the low speed buffet and the high speed buffet and I was permitted to do so too. There was about 5kts between the two. As I remember, the high speed buffet was of a sharper quality and at a slightly higher frequency - but memory does play tricks. I also suspect that each aircraft would exhibit slightly different qualities. For example, the heavy low frequency vertical motion of the 747 clean is quite different to the VC10 and 707.
Perhaps some of our test pilot colleagues could enlighten us on the stall characteristcs of different types under different conditions.
I have only once been to the aerodynamic ceiling and that was on a VC10. I was young co-pilot at the time and the training captain took it up to 46,000ft. Where he demonstrated the low speed buffet and the high speed buffet and I was permitted to do so too. There was about 5kts between the two. As I remember, the high speed buffet was of a sharper quality and at a slightly higher frequency - but memory does play tricks. I also suspect that each aircraft would exhibit slightly different qualities. For example, the heavy low frequency vertical motion of the 747 clean is quite different to the VC10 and 707.
Perhaps some of our test pilot colleagues could enlighten us on the stall characteristcs of different types under different conditions.
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I quote from the 2nd BEA report:
"The reappearance of the flight directors on the PFD when two air speeds will
be calculated that can lead the crew to rapidly engage the autopilot. However,
these speeds, though of the same order, can be erroneous and weak and thus
lead the autopilot to command movements of the flight control surfaces that
are inappropriate for the real speed of the airplane.
In case of automatic disconnection of the autothrust with activation of the
thrust lock function, the absence of appropriate manual adjustment of thrust
can present a risk of an attitude/thrust mismatch, especially when this
disconnection occurs with a low N1 value."
The same report, speaking of 13 cases of A330 airspeed anomalies:
"In seven cases, the autopilot was reconnected during the event. In two of
them, the re-connection occurred when the two speeds were consistent
with each other but were erroneous".
The A330 stall recovery procedure is to apply takeoff thrust and full aft stick, relying on the computer to maintain maximum allowable AOA. Without FBW, no pilot uses full aft stick to recover from a stall (this is usually reserved for entering a spin!). This practice is unique to an aircraft with FBW and essentially puts the pilot in a position of relying on the computer to prevent the stall (because the pilot's control input is actually trying to cause the stall). In this case, the computer may have been relying on airspeed and altitude data from 2 consistent but erroneous air data inputs and computed a maximum allowable AOA that corresponds to a lower altitude. This would be a higher AOA than should be allowed at FL350 and if full aft stick were applied would lead to a full stall. Depending on the aircraft's actual indications of a stall (something the pilots would not have experienced in training since the aircraft is "unstallable") and the fact that it was night in IMC and turbulence the crew may not have recognized the nature of the full stall and believed that the computer was preventing a full stall. I think this could have set up the situation of a deep straight-ahead stall all the way down. By the way - in the stall the drag is much higher than normal and lift much lower. This combination creates a very high sink rate, much higher than an idle power nose down descent from cruise. I think a rate of >10,000 fpm is very possible. Someone calculated a rate of 18,000 fpm from the reported information.
"The reappearance of the flight directors on the PFD when two air speeds will
be calculated that can lead the crew to rapidly engage the autopilot. However,
these speeds, though of the same order, can be erroneous and weak and thus
lead the autopilot to command movements of the flight control surfaces that
are inappropriate for the real speed of the airplane.
In case of automatic disconnection of the autothrust with activation of the
thrust lock function, the absence of appropriate manual adjustment of thrust
can present a risk of an attitude/thrust mismatch, especially when this
disconnection occurs with a low N1 value."
The same report, speaking of 13 cases of A330 airspeed anomalies:
"In seven cases, the autopilot was reconnected during the event. In two of
them, the re-connection occurred when the two speeds were consistent
with each other but were erroneous".
The A330 stall recovery procedure is to apply takeoff thrust and full aft stick, relying on the computer to maintain maximum allowable AOA. Without FBW, no pilot uses full aft stick to recover from a stall (this is usually reserved for entering a spin!). This practice is unique to an aircraft with FBW and essentially puts the pilot in a position of relying on the computer to prevent the stall (because the pilot's control input is actually trying to cause the stall). In this case, the computer may have been relying on airspeed and altitude data from 2 consistent but erroneous air data inputs and computed a maximum allowable AOA that corresponds to a lower altitude. This would be a higher AOA than should be allowed at FL350 and if full aft stick were applied would lead to a full stall. Depending on the aircraft's actual indications of a stall (something the pilots would not have experienced in training since the aircraft is "unstallable") and the fact that it was night in IMC and turbulence the crew may not have recognized the nature of the full stall and believed that the computer was preventing a full stall. I think this could have set up the situation of a deep straight-ahead stall all the way down. By the way - in the stall the drag is much higher than normal and lift much lower. This combination creates a very high sink rate, much higher than an idle power nose down descent from cruise. I think a rate of >10,000 fpm is very possible. Someone calculated a rate of 18,000 fpm from the reported information.
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On the Pitots: Icing is assumed (with good reason) to be an issue - but thinking about it - if an aircraft enters extreme weather with massive changes in pressure, wind direction etc etc - is that a possibilty of giving 'erroneous' data to the aircraft from the pitots - IE the will correctly detect a large variation in one pitot, while another MIGHT get a differing reading - or simply that massive changes were read as an error, not the actual 'aispeed' changing vastly?
Is there any thought that the airpseed data was lost for the duration of the inceident?
I know it's a 'silly' question, just wondering if system failure or ice aside, a pitot system could be 'fooled' or more precisely the computer monitoring them could think that number changes beyond a given range is incorrect?
Is there any thought that the airpseed data was lost for the duration of the inceident?
I know it's a 'silly' question, just wondering if system failure or ice aside, a pitot system could be 'fooled' or more precisely the computer monitoring them could think that number changes beyond a given range is incorrect?
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It's a nominally French airplane flown by a nominally French airline certified and investigated by a French authority, with nominally French pitot probes that are suspect..
Who would they blame - Brazil?
No, I don't expect a coverup.
GB
Who would they blame - Brazil?
No, I don't expect a coverup.
GB
Last edited by golfyankeesierra; 14th Apr 2011 at 08:03.
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Wreck orientation
Looking at the sonar image in the BEA report there is, to my mind,
a large piece of wreckage in the north east of the debris field that is high enough to produce a sonar shadow. I would hazard a guess that it is the very front part of the fuselage.
a large piece of wreckage in the north east of the debris field that is high enough to produce a sonar shadow. I would hazard a guess that it is the very front part of the fuselage.
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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.
At least in straight and level flight this process takes time.
And leaves time to react.
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Quote techgeek
What rubbish.
It is "stallable" in Alternate Law.
The stall warning (computer voiced STALL, STALL) is AOA generated, and a certain indication of the aircrafts AOA exceeding the stall AOA.
Techgeek, your previous post exposes your total lack of knowledge of the A330 flight control systems.
The A330 stall recovery procedure is to apply takeoff thrust and full aft stick, relying on the computer to maintain maximum allowable AOA.
....since the aircraft is "unstallable"....
...the fact that it was night in IMC and turbulence the crew may not have recognized the nature of the full stall and believed that the computer was preventing a full stall....
Techgeek, your previous post exposes your total lack of knowledge of the A330 flight control systems.
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Originally Posted by PJ2
I would be interested in hearing if you believe it is possible to differentiate between high speed buffet and low speed buffet at cruise altitude.
I believe that the aerodynamic 'mechanism' that I described in post #3447 is the same for high speed buffet and low speed buffet. The curves in the buffet boundary graph produced by mm43 a little while ago are continuous across the maximum at about M=0.82. That is even more apparent if you reduce these curves to a lift-coëfficient. Therefore I wouldn't expect a discontinuity in 'feel' across that maximum. EDIT: That said, it may well be that when looking at a range of Mach, say from .75 to .86, that the frequency content of buffet felt at the pilot's station changes with Mach.
Regards,
HN39
PS: The graph linked above combines in a continuous curve FCOM 3.01.20 Page 4: Buffet Boundary for 0.5<M<0.86 and Page 7: Stalling Speeds for 0.2<M<0.425 .
Last edited by HazelNuts39; 15th Apr 2011 at 08:26. Reason: PS added
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Certainly on a 737 high and low speed buffet are distinguishable as Bergerie1 says, but I would hesitate to guarantee that identification in a CB!
All this talk of descent rate and 'impact at 0215' - we do not know, do we? Until the FDR and CVR are (hopefully) read, we can 'surmise', but we don't know when impact occurred. If for any reason ACARS had stopped transmitting they could have been flying for a while!
All this talk of descent rate and 'impact at 0215' - we do not know, do we? Until the FDR and CVR are (hopefully) read, we can 'surmise', but we don't know when impact occurred. If for any reason ACARS had stopped transmitting they could have been flying for a while!
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Originally Posted by wes_wall
“Lets wait until the recorders are recovered. Then we will know.” That statement has been made ad nauseum
Regards,
HN39
Originally Posted by HarryMann
Wouldn't you need to know exactly how deep was the penetration of the sea surface? Have we any information on 'compliance' at water surfaces in these cases.
Originally Posted by Machinbird
From my recollection, he described stall behavior of these aircraft as a low frequency vibration with increasing motion on the flight deck until it reached the point that was mandatory that the crew be strapped in or else they would be thrown from their seats. This type behavior would likely be also relevant to the A332.
Originally Posted by Bergerie1 (#3473)
I relate all this because of the discussion in previous posts about whether the pilots could have distinguished between pre stall buffet and the turbulence associated with thunderstorms. I think the answer is in most cases 'yes', the two are distinguishable. However, in heavy turbulence it is highly probable that the pre stall buffet would be 'lost' in the general ambient turbulence.
And in really heavy turbulence one's brains feel rather 'scrambled' which would make it even more difficult! In which case it is quite possible that the pilots on AF447 would not have been able to discern the pre stall buffet.
And in really heavy turbulence one's brains feel rather 'scrambled' which would make it even more difficult! In which case it is quite possible that the pilots on AF447 would not have been able to discern the pre stall buffet.
techgeek, if I may critique your presentation:
Originally Posted by techgeek
The A330 stall recovery procedure is to apply takeoff thrust and full aft stick, relying on the computer to maintain maximum allowable AOA.
If I am correct in understanding how pilots are trained, what you are calling stall recovery is actually recovery from approach to stall, then full power and Max Allowable AoA ... which will keep you from stalling, and get you out of near occasions of stall.
Once you actually stall, you have to REDUCE AoA (or you will remain stalled) which probably can't be done with aft stick, unless you are flying inverted ... which I don't think you'll find people doing in the A330.
You appear to have mixed and matched stall recovery and stall prevention.
Without FBW, no pilot uses full aft stick to recover from a stall (this is usually reserved for entering a spin!).
This practice is unique to an aircraft with FBW and essentially puts the pilot in a position of relying on the computer to prevent the stall (because the pilot's control input is actually trying to cause the stall).
Do you see from the bolded bits why I think you are mixing apples and oranges?
More to the point, I disagree with your assertion that using max power and high (but not stalled) AoA is confined to FBW aircraft.
I used to teach a recovery from an approach turn stall (practiced at altitude, gear and flaps down) in which you deliberately enter a stall in a balanced turn, and you then ...
lower the nose (AoA) and level the wings
max power
raise nose to high AoA
eventually establish a rate of climb
I also used to do the following in the landing pattern to test stall prevention on safe for solo checks:
I'd hit the AoA test button briefly, to get the rudders to shake. In that training plane rudder shakers (like stick shakers in some commercial transport aircraft) was a warning of impending stall (AoA at about 26 units, stall typically at 29 units) . I would look for the following response (stall prevention): wings level, full power, climbing attitude ... with the idea being that if your approach to landing was close to stall, it was time to wave off (go around) and try again.
HazelNuts pointed out a few posts back that if AF 447 were stalled, the A330's robot voice would have been advising the pilots (with annoying repetition) that they had stalled. So my concern about "would they recognize the stall," and Bergerie1's point about what heavy turbulence might do to body senses, have already been answered by the aircraft's designers by using AoA to trigger "You are stalled!!!!" warnings in unambiguous terms. You'd think that stall recovery would begin with a move to reduce AoA, yes? The FDR's will hopefully tell us if that is true or not, in due course.
[/QUOTE]
Originally Posted by bia botal (#3480)
Theres another scenario to consider then isn't there,
that the aircraft was turning,
perhaps they considered the best way out of a storm cell that they didn't know was there is the way they came in,
a turning aircraft with the handling pilot trying to reduce speed (my note: why trying to reduce speed? Turbulence/CB penetration considerations?)
that appears not to be whilst the aircraft is descending due to downdrafts may have been attempting to trade off speed to maintain some height, only speed is not reducing,
with thrust at idle, (my note: why thrust at idle?)
nose attitude high, (my note: why nose high?)
severe turbulence, and bank angle,(perhaps exaggerated by turbulence)
how long to stall now?
that the aircraft was turning,
perhaps they considered the best way out of a storm cell that they didn't know was there is the way they came in,
a turning aircraft with the handling pilot trying to reduce speed (my note: why trying to reduce speed? Turbulence/CB penetration considerations?)
that appears not to be whilst the aircraft is descending due to downdrafts may have been attempting to trade off speed to maintain some height, only speed is not reducing,
with thrust at idle, (my note: why thrust at idle?)
nose attitude high, (my note: why nose high?)
severe turbulence, and bank angle,(perhaps exaggerated by turbulence)
how long to stall now?
Your event chain leaves me scratching my head.
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Originally Posted by teckgeek
I quote from the 2nd BEA report:
"The reappearance of the flight directors on the PFD when two air speeds will
be calculated that can lead the crew to rapidly engage the autopilot. However,
these speeds, though of the same order, can be erroneous and weak and thus
lead the autopilot to command movements of the flight control surfaces that
are inappropriate for the real speed of the airplane.
In case of automatic disconnection of the autothrust with activation of the
thrust lock function, the absence of appropriate manual adjustment of thrust
can present a risk of an attitude/thrust mismatch, especially when this
disconnection occurs with a low N1 value."
The same report, speaking of 13 cases of A330 airspeed anomalies:
"In seven cases, the autopilot was reconnected during the event. In two of
them, the re-connection occurred when the two speeds were consistent
with each other but were erroneous".
"The reappearance of the flight directors on the PFD when two air speeds will
be calculated that can lead the crew to rapidly engage the autopilot. However,
these speeds, though of the same order, can be erroneous and weak and thus
lead the autopilot to command movements of the flight control surfaces that
are inappropriate for the real speed of the airplane.
In case of automatic disconnection of the autothrust with activation of the
thrust lock function, the absence of appropriate manual adjustment of thrust
can present a risk of an attitude/thrust mismatch, especially when this
disconnection occurs with a low N1 value."
The same report, speaking of 13 cases of A330 airspeed anomalies:
"In seven cases, the autopilot was reconnected during the event. In two of
them, the re-connection occurred when the two speeds were consistent
with each other but were erroneous".
CONFiture
Is there reason to believe that AF 447 was operating at a low N1 value? 
From the excerpt techgeek cited, my instinct was to presume (perhaps incorrectly) that the risks of this problem would tend to be greater during landing.
That said,
... thus lead the autopilot to command movements of the flight control surfaces that are inappropriate for the real speed of the airplane.
appears to be what Svarin was alluding to a few dozen posts back.
The prospect is scary, be ye pilot or be ye pax.
... the absence of appropriate manual adjustment of thrust can present a risk of an attitude/thrust mismatch, especially when this disconnection occurs with a low N1 value."
From the excerpt techgeek cited, my instinct was to presume (perhaps incorrectly) that the risks of this problem would tend to be greater during landing.
That said,
... thus lead the autopilot to command movements of the flight control surfaces that are inappropriate for the real speed of the airplane.
appears to be what Svarin was alluding to a few dozen posts back.
The prospect is scary, be ye pilot or be ye pax.
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Originally Posted by Lonewolf_50
Is there reason to believe that AF 447 was operating at a low N1 value?
*Click*
The lightbulb just went on.
Thanks.
The lightbulb just went on.
Thanks.
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force of 100 g-load`s
Quote:
15~20,000 ft/min: I suppose I ought to do the stubby pencil math and see how that fits in with BEA's estimated g-loads at impact.
Wouldn't you need to know exactly how deep was the penetration of the sea surface? Have we any information on 'compliance' at water surfaces in these cases.
15~20,000 ft/min: I suppose I ought to do the stubby pencil math and see how that fits in with BEA's estimated g-loads at impact.
Wouldn't you need to know exactly how deep was the penetration of the sea surface? Have we any information on 'compliance' at water surfaces in these cases.
if you stopp a falling pelvis with a vertical speed of 15000 ft/min (15000*0,3/60 =75 m/sec) with a constant force of 100 g-load`s (100g=981m/sec˛) it stopps to zerro after 75/981= 0,076 sec and a way of less than 3m !
water is nearly incompressible at this speed, (within 0,07 sec it can not move much to the side), it makes not realy a grate difference if you crash into concrete or water with 75m/sec !
and this very short stoppway is plausible:
ca. 3m will be the sum of the compressible space between the pelvis and the water, (the space under the seat, the airspace into the baggage compartment, and the construction space in the lower fuselage.....)
grity