Habsheim
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Originally Posted by gums
max AoA was always there if we pulled full back on the sidestick. No auto-throttle, but that was up to us. The jet gave you everything it could.
What strikes me is how in Habsheim, New-York or Bilbao, the pitch authority has been compromised by features built into the system, whenever the aerodynamic had still more to deliver.
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Originally Posted by Machinbird
Why would he pull the throttles all the way back? I'm not an Airbus guy so I'm curious as to the reasoning.
When I pushed initially the thrust levers to an intermediate position when arriving above the Habsheim field, the N1 command was elaborated with the previously demonstrated delay, which I interpreted as a non response from the engines. Instinctively, I recycled the levers to the IDLE then TOGA position.
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And pushing the thrust levers to said intermediate position would have taken place about six seconds before TOGA thrust was commanded. Unfortunately there is no evidence of it on the flight recorders. As the Airbus presentation on Habsheim phrases it:
Possible explanations for this discrepancy (ignoring the extreme assumptions that Asseline ist just a liar or that the whole investigation was rigged to protect Airbus):
Only one thrust lever movement is shown after flight idle is selected at the commencement of the descent, and concurrently with the clicks being heard, at 4.5 seconds before the aircraft enters the trees.
- Asseline honestly believes that he commanded intermediate thrust at the transition from descent to level flight, but he never really did.
- He did, but the thrust levers failed in such a way that not even thrust lever angle as recorded by the DFDR reflected the change.
@conf
WRT to my comment about getting max performance when commanding max performance in the Viper....
Which features compromise the pilot's command for max performance?
I also wonder if there were connections with the throttle implementation ( think Asiana) that the pilot did not expect, hence trying to "re-cycle" the system?
Secondly, our primitive system did not require full stick forward or back to command max AoA. As with the 'bus, it was a gee command, and of approx one gee per 4 pounds of stick pressure ( no movement, just pressure sensors), limited by AoA, so at max AoA all we could command was one gee even with 34 pounds of back stick pressure! In short, we could have duplicated the crash into the trees if power-limited and too slow. Hence my question about the throttle implementation.
Thanks ahead of time.
WRT to my comment about getting max performance when commanding max performance in the Viper....
In theory, the Airbus is not different, as the procedure is to rely on the protections to get the most out of it, but as I wrote earlier :
What strikes me is how in Habsheim, New-York or Bilbao, the pitch authority has been compromised by features built into the system, whenever the aerodynamic had still more to deliver
What strikes me is how in Habsheim, New-York or Bilbao, the pitch authority has been compromised by features built into the system, whenever the aerodynamic had still more to deliver
I also wonder if there were connections with the throttle implementation ( think Asiana) that the pilot did not expect, hence trying to "re-cycle" the system?
Secondly, our primitive system did not require full stick forward or back to command max AoA. As with the 'bus, it was a gee command, and of approx one gee per 4 pounds of stick pressure ( no movement, just pressure sensors), limited by AoA, so at max AoA all we could command was one gee even with 34 pounds of back stick pressure! In short, we could have duplicated the crash into the trees if power-limited and too slow. Hence my question about the throttle implementation.
Thanks ahead of time.
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Originally Posted by gums
Which features compromise the pilot's command for max performance?
- Hudson - Phugoid damping
- Bilbao - Logic in the AOA protection in case of turbulent conditions
- Habsheim - Radio silence ...
I also wonder if there were connections with the throttle implementation ( think Asiana) that the pilot did not expect, hence trying to "re-cycle" the system?
- During the take off run, the system bizarrely requested to set the thrust levers to the CLB position.
- At 1000 AGL when it was time to set the thrust levers to the CLB position, the N1 command did not follow the request and remained to the previous setting. Asseline had to retard the levers behind the CLB position, only then the N1 command was elaborated but not without delay.
- Nothing of this is mentioned in the BEA report.
- The final report does not even include the FDR data for that flight portion.
Thanks, Conf
I'll have to dig out my FCOM stuff from the AF447 files and see how that throttle works.
Of course, a few practice flyby runs may have shown any problems with the throttle mechanization.
I'll have to dig out my FCOM stuff from the AF447 files and see how that throttle works.
Of course, a few practice flyby runs may have shown any problems with the throttle mechanization.
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Originally posted by CONF iture..At 1000 AGL when it was time to set the thrust levers to the CLB position, the N1 command did not follow the request and remained to the previous setting. Asseline had to retard the levers behind the CLB position, only then the N1 command was elaborated but not without delay.
Last edited by Goldenrivett; 11th Jan 2014 at 12:36.
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Originally Posted by Goldenrivett
To do a flight idle fly pass and hope the engines spooled up when requested (with the knowledge of the known thrust problem on take off), does not seem to be prudent to me.
Second observation is :
Why the BEA is hiding the malfunction ?
What else are they hiding ?
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Why the BEA is hiding the malfunction ?
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It did not, it's all in the CVR transcript. At 12:41:19 the captain comments that he knows about that 'bug' and at 12:42:12 that it is because he has reduced below a certain N1.
I'd think they would want to address how that specific feature works and what influence it may have had with respect to the delayed power response.
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Originally Posted by HN39
It did not, it's all in the CVR transcript. At 12:41:19 the captain comments that he knows about that 'bug' and at 12:42:12 that it is because he has reduced below a certain N1.
Originally Posted by Machinbird
Was this discussed in the Body of the BEA report?
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Originally Posted by CONF iture
Originally Posted by HN39
It did not, it's all in the CVR transcript. At 12:41:19 the captain comments that he knows about that 'bug' and at 12:42:12 that it is because he has reduced below a certain N1.
Originally Posted by Machinbird
Was this discussed in the Body of the BEA report?
Originally Posted by i.e. BEA Report Habsheim
:
[ ]
4.3 Aéronef
4.3.1. La commission a constaté que certaines anomalies de fonctionnement n'ayant joué aucun rôle dans l'accident (défauts mentionnées dans les compte rendus mécaniques) avaient été corrigées depuis sur les appareils en service. Elle n'estime donc pas avoir à formuler de recommandation a leur sujet. (sic)
[ ]
[ ]
4.3 Aéronef
4.3.1. La commission a constaté que certaines anomalies de fonctionnement n'ayant joué aucun rôle dans l'accident (défauts mentionnées dans les compte rendus mécaniques) avaient été corrigées depuis sur les appareils en service. Elle n'estime donc pas avoir à formuler de recommandation a leur sujet. (sic)
[ ]
Last edited by roulishollandais; 11th Jan 2014 at 22:34. Reason: quote brackets
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Report approved with unanimity by the members of the enquiry commission :
Claude Bechet, François Gonin, Bernard Farthouat, Robert Auffret, Philippe Gourguechon, Paul Arslanian, jean-Paul de Villeneuve
Claude Bechet, François Gonin, Bernard Farthouat, Robert Auffret, Philippe Gourguechon, Paul Arslanian, jean-Paul de Villeneuve
Thread Starter
Alleged thrust discrepancies (1)
Quote from CONF_iture (my clarification in square brackets):
"Two different things related to the thrust system happened earlier :
(1) During the take off run, the system bizarrely requested to set the thrust levers to the CLB position.
(2) At 1000 AGL [roughly top of climb] when it was time to set the thrust levers to the CLB position, the N1 command did not follow the request and remained to the previous setting. Asseline had to retard the levers behind the CLB position, only then the N1 command was elaborated but not without delay."
Before I read the captain's memoir, I may be able to explain (1), and I've some observations on (2).
(1) In the early months of A320 airline operation, we had quite a lot of minor glitches on the FMGS. The PERF page includes separate figures for thrust-reduction and acceleration altitudes, the defaults of which are either 1000 ft or 1500 ft above the departure aerodrome, but each can be amended manually before T/O. Basle (LFSB/BSL) is 883 ft amsl, so the default settings may have been 1900/1900. AFAIK, the only function of the THR RED function is to provide an aide-memoire for the crew to reduce to climb thrust (if both donks are still running), which it does by a flashing "CLB" in amber on both pilots' thrust FMA.
The glitch was that the THR RED figure would be lost just after take-off thrust was commanded on T/O, leading to an immediate flashing CLB prompt. This was distracting, but had no effect on engine performance.
(2) After T/O the L/G was retracted in the normal way. After climbing only 1100 ft, the short cruise was conducted at 2000 ft QNH, i.e., roughly 2000ft amsl, maintaining the T/O Flap setting of 1+F (Slats 18 deg, Flaps 10), so ALT* (altitude-capture mode) would have been triggered well below it, pre-empting the acceleration phase for the FDs, which seem to have been in use. "Alt Star" was called by the copilot at 12:41:47, about 17 seconds after airborne, and his call may have been some seconds after the mode change.
At ALT*, the thrust would have needed to be reduced immediately and substantially below CLB thrust, to avoid exceeding the flap limiting speed. (With Habsheim so close, an IAS of about 185 kt would have been reasonable.) In fact, the CVR recorded sounds of thrust reduction starting 5 sec after reaching 2000 ft. At that point, the A/THR was still engaged, and would have changed to SPD (speed) mode because of ALT*. So the thrust reduction would have been achieved by resetting the speed to a figure at or below the current IAS, and/or by retarding the thrust levers well behind the CLB gate, thereby introducing an upper thrust limit less than CLB. (Partially retarding the thrust levers to the desired N1 would in either case have been desirable before changing to manual thrust.)
A/THR was in fact disengaged about 8 sec after start of thrust reduction, and happened to coincide with a L/G CRC warning. The latter would have been caused by a combination of N1 < 75% and radio height < 1000ft, (as the captain intimated, although my 1988 FCOM states < 750 ft). There were some low hills to their left at this point.
So, prior to reading Capt Asseline's account, I see no evidence of anomalies of engine performance in the T/O, climb or cruise phases. I agree with CONF_iture, however, that it would be good to see the DFDR for the whole flight.
"Two different things related to the thrust system happened earlier :
(1) During the take off run, the system bizarrely requested to set the thrust levers to the CLB position.
(2) At 1000 AGL [roughly top of climb] when it was time to set the thrust levers to the CLB position, the N1 command did not follow the request and remained to the previous setting. Asseline had to retard the levers behind the CLB position, only then the N1 command was elaborated but not without delay."
Before I read the captain's memoir, I may be able to explain (1), and I've some observations on (2).
(1) In the early months of A320 airline operation, we had quite a lot of minor glitches on the FMGS. The PERF page includes separate figures for thrust-reduction and acceleration altitudes, the defaults of which are either 1000 ft or 1500 ft above the departure aerodrome, but each can be amended manually before T/O. Basle (LFSB/BSL) is 883 ft amsl, so the default settings may have been 1900/1900. AFAIK, the only function of the THR RED function is to provide an aide-memoire for the crew to reduce to climb thrust (if both donks are still running), which it does by a flashing "CLB" in amber on both pilots' thrust FMA.
The glitch was that the THR RED figure would be lost just after take-off thrust was commanded on T/O, leading to an immediate flashing CLB prompt. This was distracting, but had no effect on engine performance.
(2) After T/O the L/G was retracted in the normal way. After climbing only 1100 ft, the short cruise was conducted at 2000 ft QNH, i.e., roughly 2000ft amsl, maintaining the T/O Flap setting of 1+F (Slats 18 deg, Flaps 10), so ALT* (altitude-capture mode) would have been triggered well below it, pre-empting the acceleration phase for the FDs, which seem to have been in use. "Alt Star" was called by the copilot at 12:41:47, about 17 seconds after airborne, and his call may have been some seconds after the mode change.
At ALT*, the thrust would have needed to be reduced immediately and substantially below CLB thrust, to avoid exceeding the flap limiting speed. (With Habsheim so close, an IAS of about 185 kt would have been reasonable.) In fact, the CVR recorded sounds of thrust reduction starting 5 sec after reaching 2000 ft. At that point, the A/THR was still engaged, and would have changed to SPD (speed) mode because of ALT*. So the thrust reduction would have been achieved by resetting the speed to a figure at or below the current IAS, and/or by retarding the thrust levers well behind the CLB gate, thereby introducing an upper thrust limit less than CLB. (Partially retarding the thrust levers to the desired N1 would in either case have been desirable before changing to manual thrust.)
A/THR was in fact disengaged about 8 sec after start of thrust reduction, and happened to coincide with a L/G CRC warning. The latter would have been caused by a combination of N1 < 75% and radio height < 1000ft, (as the captain intimated, although my 1988 FCOM states < 750 ft). There were some low hills to their left at this point.
So, prior to reading Capt Asseline's account, I see no evidence of anomalies of engine performance in the T/O, climb or cruise phases. I agree with CONF_iture, however, that it would be good to see the DFDR for the whole flight.
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Achieving actual ultimate performance
Originally Posted by Gums
Secondly, our primitive system did not require full stick forward or back to command max AoA. As with the 'bus, it was a gee command, and of approx one gee per 4 pounds of stick pressure ( no movement, just pressure sensors), limited by AoA, so at max AoA all we could command was one gee even with 34 pounds of back stick pressure! In short, we could have duplicated the crash into the trees if power-limited and too slow. Hence my question about the throttle implementation.
That would only apply to level flight. I would hope you could still pull a fractional g load if headed straight up and needing to ease the nose over-
A related question however:
Did your system allow you to pull right into buffet, or did it keep you out of the buffet boundary? How much of your ultimate potential performance did it let you have? Did some Vipers turn a little bit better than others?
I ask this from the vantage point of a Phantom Pflyer where if the outer wing panels weren't shaking, you were not asking for maximum performance!
I'd think that the A320 would not be allowed to enter the buffet boundary to keep from scaring the cargo, but I could be wrong. (Normal Law)
Buffet would more likely be encountered in clean configuration if it is possible to achieve the buffet boundary.
With flaps/slats down, there may not be a buffet boundary or a very minimal one.
Last edited by Machinbird; 12th Jan 2014 at 01:23. Reason: Add qualifier
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Extracted from VFW614 ATTAS Hi AoA protection tests: LINK
High AOA Protection (dynamic)
Fig. 18 shows that the high AOA protection operates precisely even in dynamic maneuvers, such as the side stick full back step input at VCAS = 180kts.
The aircraft reacts with a ∆nZ =0.8g pitch up movement up to 22° pitch attitude.
The high AOA protection counters this dynamic nose-up maneuver with a 4° nose down elevator command.
The aircraft stabilizes at α= αlim and VCAS = Vαlim.
In neither of the high AOA protection tests the maximum angle-of-attack αlim has been exceeded.
Fig. 18 shows that the high AOA protection operates precisely even in dynamic maneuvers, such as the side stick full back step input at VCAS = 180kts.
The aircraft reacts with a ∆nZ =0.8g pitch up movement up to 22° pitch attitude.
The high AOA protection counters this dynamic nose-up maneuver with a 4° nose down elevator command.
The aircraft stabilizes at α= αlim and VCAS = Vαlim.
In neither of the high AOA protection tests the maximum angle-of-attack αlim has been exceeded.
Last edited by A33Zab; 12th Jan 2014 at 10:48. Reason: Corrected link
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erratum post 304
I just edited my post 304.
I replaced (Chris Scott link) to "rudderrudderrat link post 269".
Apologize to both.
That link with the 3 definitions of stall was :
http://lessonslearned.faa.gov/Indian...0Condition.pdf
... new edit : after rereading all that, I find NO definitive definition of stall, only rumours
I replaced (Chris Scott link) to "rudderrudderrat link post 269".
Apologize to both.
That link with the 3 definitions of stall was :
http://lessonslearned.faa.gov/Indian...0Condition.pdf
... new edit : after rereading all that, I find NO definitive definition of stall, only rumours
Last edited by roulishollandais; 13th Jan 2014 at 16:01.
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Hi A33Zab,
Long time no see! Thanks for the graph amd the link to the DASA/NLR report on the ATTAS-SAFIR research project. A valuable contribution to the never ending Habsheim debate and the intriguing questions still posed 25 years later.
Long time no see! Thanks for the graph amd the link to the DASA/NLR report on the ATTAS-SAFIR research project. A valuable contribution to the never ending Habsheim debate and the intriguing questions still posed 25 years later.
@ 'bird: Sorry, I needed to make it clear that I could have duplicated the crash, as even with max back stick, my jet would only hang at 27 deg AoA and 1 gee. No way to command a higher AoA or gee. Biggest difference was no autothrottle modes and such. Push forward, motor spools up. Pull back, motor spools down. Unlike the GE J-79, both the fans I flew ( A-7D and F-16A) spooled up very slowly, in comparison. At max AoA and low altitude, I had plenty of thrusties left over, so a go around was easy. Aftr reading the India 605 discussion, I got a better understanding of the autothottle, and I see why the Captain under scrutiny here pulled back and then advanced to ensure he was out of the autothrottle system. Too late. He had plenty of excess thrust available, but "pressed" too hard and too long.
Secondly --- No real buffet in the Viper at max AoA. Kinda a low freq buzz. This was due to the leading edge flaps moving all the time, eventually reaching full down above a certain AoA. Provided excellent directional and lateral stability - like full aileron command and 250 - 300 deg/sec roll rate all without departing.
Last answer for the 'bird -- - could always push to a lower gee unless in a deep stall. The lack of pronounced buffet and the loss of the nose down pitch authority we had in a deep stall was the main reason I joined the AF447 crowd. Although the 'bus still has nose down authority when deeply stalled, our contributors here have shown it takes a long time to finally get flying again. Unlike the 'bus, we trimmed for a gee with either a small wheel or the coolie hat. We did not have the 'bus implementation. If I let go of the stick, the sucker tried to get to whatever gee I had it trimmed for. Did this at any attitude.
Didn't mean to repeat what I had posted on AF447, but simply answered the 'bird's question and added an opinion of the Captain's actions/judgement.
Secondly --- No real buffet in the Viper at max AoA. Kinda a low freq buzz. This was due to the leading edge flaps moving all the time, eventually reaching full down above a certain AoA. Provided excellent directional and lateral stability - like full aileron command and 250 - 300 deg/sec roll rate all without departing.
Last answer for the 'bird -- - could always push to a lower gee unless in a deep stall. The lack of pronounced buffet and the loss of the nose down pitch authority we had in a deep stall was the main reason I joined the AF447 crowd. Although the 'bus still has nose down authority when deeply stalled, our contributors here have shown it takes a long time to finally get flying again. Unlike the 'bus, we trimmed for a gee with either a small wheel or the coolie hat. We did not have the 'bus implementation. If I let go of the stick, the sucker tried to get to whatever gee I had it trimmed for. Did this at any attitude.
Didn't mean to repeat what I had posted on AF447, but simply answered the 'bird's question and added an opinion of the Captain's actions/judgement.
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A33zab
Yes, thanks for that link and graph. I see that for quite a time the elevator was moving downwards and the AOA dropping even though the sidestick was being held fully back. Hmmmm!
Yes, thanks for that link and graph. I see that for quite a time the elevator was moving downwards and the AOA dropping even though the sidestick was being held fully back. Hmmmm!