I was wondering if you could clarify a bit what you meant by "...why does the computer air data program attach quite so much importance to pitot static airspeed?".
What I meant here was as I recall when the airspeed data corrupted, the aircraft went into alternate law mode, which seems to have added to the crew confusion, yes you are right about the stab trimming nose up due to the sidestick input, but I understood this trimming happened automatically under the "alternate law", recovering from a stall with full up stab trim would vastly confuse things. This is what I meant by "so much importance to IAS", to me it seems there should be more parameters measured, before he system reverts to alternate law? For example shock stall and crit alpha stall cause the same symptoms as such (buffet), and with a falty IAS reading in IMC, the only sure way to tell the difference is AoA? If the crew had had this, would they have realised they were at low speed, not overspeed? This may have been discussed earlier, but this was a very interesting accident (very tragic too), as it touches on the clash between classic stick and rudder skills, and modern aircraft AP systems. (By the way, how do you do a quote on a forum post? I looked in FAQ but no luck? I am anashamedly a very pre computer ager, when I joined the air force, the most odern piece of kit on the Sqn was a hand cranked copier!) |
This has all been covered in the mega-threads, so I'll go over this once only for the sake of my sanity... :ok:
Originally Posted by PerAsperaAdAstra
(Post 8580170)
What I meant here was as I recall when the airspeed data corrupted, the aircraft went into alternate law mode, which seems to have added to the crew confusion...
Alternate Law should be neither confusing nor a big deal - in a pinch all you need to remember is that the "hard" protections are no longer there - i.e. it's possible to stall or spiral dive the aircraft if you overcontrol (just like a conventional aircraft), and that depending on the mode you're in, the aircraft will be slightly more sensitive in roll. In short, all it means is fly normally but be careful with the controls. you are right about the stab trimming nose up due to the sidestick input, but I understood this trimming happened automatically under the "alternate law", recovering from a stall with full up stab trim would vastly confuse things. http://www.pprune.org/tech-log/46062...ml#post6793521 This is what I meant by "so much importance to IAS", to me it seems there should be more parameters measured, before he system reverts to alternate law? it touches on the clash between classic stick and rudder skills, and modern aircraft AP systems. (By the way, how do you do a quote on a forum post?) |
Thanks Dozy, you seem anything but! Interesting stuff the 447 case. One last question, the sidestick, is it programmed to give a stick force feel, (I think it is?), and will it show sloppiness at low speed, tightening up at high speed as such? Why the need to autotrim the stab with sidestick input? It seems to me a better option to let the FP choose the option surely?
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Originally Posted by PerAsperaAdAstra
(Post 8580209)
Thanks Dozy, you seem anything but!
One last question, the sidestick, is it programmed to give a stick force feel, (I think it is?), and will it show sloppiness at low speed, tightening up at high speed as such? Why the need to autotrim the stab with sidestick input? |
"Another AF447"? Not even slightly West Caribbean Airways Flight 708 - Wikipedia, the free encyclopedia Captain flying this time. |
@Oakape: Yup - we covered that on the megathread. What's interesting there is that WCA708 provides an instance of rebuttal to the "connected controls" argument, as that aircraft (an MD-80) had connected yokes, and the PNF still didn't see (or respond to the evidence) that his Captain was in fact pulling harder into the stall. Also that the MD-80's automation was not sophisticated enough to detect that it could not maintain the requested altitude with the engine thrust reduced by the anti-ice system.
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The issue is that we're not given any context as to what that sim session was about. That series was broadcast in 1996.
In general, Black Box was an excellent series, and I still have it kicking around on VHS somewhere - however in this episode it does make the mistake of assuming the technology of the time was a first step in removing the pilot, which was never true. |
Originally Posted by DozyWannabe
(Post 8583861)
@Oakape: Yup - we covered that on the megathread. What's interesting there is that WCA708 provides an instance of rebuttal to the "connected controls" argument, as that aircraft (an MD-80) had connected yokes, and the PNF still didn't see (or respond to the evidence) that his Captain was in fact pulling harder into the stall. Also that the MD-80's automation was not sophisticated enough to detect that it could not maintain the requested altitude with the engine thrust reduced by the anti-ice system.
Not a technical point, this being Tech Log, other than the matter of technical training associated with operating complex machines. |
Winnerhofer:
Stall warning is set to occur before natural (aerodynamic) buffet starts. The stall warning threshold is approximately 1 deg less than the buffet onset AoA. At 7 - 8 degrees the airplane would be well into buffet: http://i.imgur.com/Qe96igD.jpg?1 P.S. Although the EICAS is for system failures rather than pilot errors, perhaps a message like: "STALL: RELEASE STICK OR PUSH" would help a disoriented pilot? |
Originally Posted by Winnerhofer
(Post 8595171)
Is the SW programmed to kick in @ 5.8° AOA too early?
Originally Posted by Lonewolf_50
(Post 8595394)
Incidents like the one cited argue for better training on stall, incipient stall, stall recognition, and recovery regardless of make and model.
Not a technical point, this being Tech Log, other than the matter of technical training associated with operating complex machines. |
incidents like WCA708 and Birgen301 provide a useful counterpoint to those who reflexively claimed that AF447 would not have happened on a Boeing/MD with linked yokes No one is seriously saying AF447 would not have happened in a Boeing. However, many experienced pilots here have explained how a yoke may have helped the pilots achieve a better outcome. Let them have their opinion – jeez |
Sorry for a non-pilot making a statement here. The father in law of a good friend of mine was an airline pilot with 25+ years of experience. He started originally on Tu-154 then transferred to B-737 for many years. Then he was supposed to be retrained to Airbus due to changes in the fleet of the carrier he worked for.
He expressed many times his disappointment with FBW environment with sidestick without feedback from control surfaces and said that this is not old school flying anymore and the joy of flying is gone. Making the long story short the pilot ended his life by suicide. It would be very inappropriate to claim that the old guy decided to leave the world just because of necessity to change to new type of a/c with SS but as the family says he was very bitter with the fact. It is known that suicide cases have (like accidents) more contributing factors. Also this is not an attempt to make a flame war regarding Boeing and Airbus proponents. What I can say as a consultant which is partly involved with safety in various industries - if the operator on any machine or vehicle doesn't like the controls of it then he is more prone to accidents. Now back to pro pilots :O |
Originally Posted by Cool Guys
(Post 8597206)
No one is seriously saying AF447 would not have happened in a Boeing.
However, many experienced pilots here have explained how a yoke may have helped the pilots achieve a better outcome. Let them have their opinion – jeez In theory, the connected yokes should provide an extra cue in the visual and tactile channels, but in practice it doesn't seem to make a great deal of difference. What this means is that no matter what anyone's personal feelings are on the matter, both designs are - as near as we can tell - pretty damned safe, and that the various pros and cons of each are immaterial in real terms. |
yeah, Ive read the "mega" thread. There are many interesting and valid opinions from some smart and experienced people.
Because the sample base is very small, a comparison based on statistical evidence has minimal value. |
@Cool Guys - Right - and I remember your posts on the subject and others. If I recall correctly, you're an engineer with an interest, like me.
Experience and intelligence are definitely good things - however the best kind of experience also comes with a continued desire to learn and evaluate changing circumstances. An experienced person who reflexively dismisses a different paradigm as inferior without properly evaluating it is as potentially dangerous as a less experienced person who blindly accepts each change as inherently better. @Winnerhofer - The MD-80's pitot-static system does not automatically cross-check for data validity in the same way as the FBW Airbus system does. I don't think the author of your linked article is aware of that fact. |
I haven't got all the facts at my fingertips as I sit here now, will go over the info I have when I get the chance but 447 seems to tie in with the A320 LOC when carrying out an acceptance test flight for the return of the aircraft to service with Air to New Zealand. As I recall, an unplanned approach to the stall was carried out, as IAS was reduced, the aircaft systems trimmed the tailplane full nose up, just before the stall, the engines were powered up, but due to the up trim and the nose up pitch caused by the engine thrust lines on pod engines, the aircraft did not respond to recovery nose down side stick input as was expected. This caused confusion resulting in a relaxing of the nose down input. The aircraft subsequenty stalled and crashed into the ocean.
It seems to me the synthetic feel of the sidestick was an issue, can't help but feel a good old Boeing style yolk would have removed all doubt of what control input and to what extent, was being made? Would like to have a go at a sidestick if I got the chance, as I do regard them with some suspicion...along the lines of, it's all good as long as things are ops normal :hmm:...but when things are going wrong...:uhoh: |
Hi Dozy,
In industries that produce equipment that can kill people if it goes wrong, those who are careful about adopting new non validated technologies pose far fewer risks than those who accept new technologies without proper evaluation. |
@Cool Guys - Correct, but I'd say a decade of development and testing (from the Concorde "minimanche" experiments in the mid-'70s onwards) constitutes a very rigorous evaluation process, even by aviation standards.
26 years since the A320 went into service and the number of hull-losses attributable to the FBW system and the flight deck design on all Airbus FBW types remains at zero. The Airbus FBW types have a safety record that compares very respectably with other types and thousands of the things fly daily. So I'd say that the worst fears of the more reactionary "experienced" pilots back when the A320 was launched haven't come to pass, and on this occasion they were wrong about a lot of things. |
PerAAA #275
" aircraft trimmed nose up..." " thrust lines on pod engines..." How often does one include a visual check of the current state of the trim whilst in normal flight, when it is all done automatically for you ? How often do you have the opportunity to alter the power from cruising power to flight idle and then back to climb power - whilst in level flight, to see what happens ? One of the many performance graphs for AF447 appeared to show that power was reduced to Flight Idle - and the nose dropped for a few seconds (as it must). Then TOGA was restored. IIRC this was a few second prior to the final stall. ( I think that nothing was said at the time on the CVR by PF or PNF. The Captain was called at about this time.) |
Originally Posted by DozyWanabee
safety record
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