Go Back  PPRuNe Forums > Flight Deck Forums > Tech Log
Reload this Page >

AF447 Thread No. 3

Tech Log The very best in practical technical discussion on the web

AF447 Thread No. 3

Old 13th Jun 2011, 21:58
  #1941 (permalink)  
 
Join Date: Aug 2009
Location: Texas
Age: 64
Posts: 7,197
Received 393 Likes on 244 Posts
For eSpoiler:
I hope this hasnt already been discussed

It has, since about as soon as the ACARS information became available to, (or was leaked to), the public.

In the aftermath of the accident the plethora of automated signals sent from the doomed aircraft were widely publicised. Has this information been compared to the details of the accident released so far and in particular the time line provided by the BEA?
Between the date of release and the day the FDR data began to become available, the ACARS data were dissected minutely on these forums ... three threads in the Tech Log forum, and two in the regular forum (or maybe one got moved to here). Happy reading. I've slogged through it all, over the past year and a half, and while there is a lot of noise, there is also some very useful signal.

Remember: ACARS is a system intended to inform the manitenance shop what things were going wrong while the plane was flying, so they can have repair or replace options ready when the aircraft arrives at the next maintenance facility. The more I learn about it, the more useful I think it is for the paying customers. Faster turn around times and fewer things not working between stops could be a benefit of this system ... except of course for things that require major repair.
In my laypersons opinion, surely a comparison would yield some additional insight into what the pilots experienced and what caused the tragedy.
As noted above, pounded into the pavement. I suggest to you that the BEA are using all of it, and comparing it to what else they know, have found out, or infer.

As an aviation enthusiast and very part time passenger, it boggles my mind that a modern automated aircraft could get stalled at 35 000 ft + and not carry on flying at some point before crashing.
You are not alone. Most pilots are puzzled by that as well ... the search into "what happened?" has filled a whole lot of bandwidth, and many pages on these forums.
Lonewolf_50 is offline  
Old 13th Jun 2011, 22:05
  #1942 (permalink)  
bearfoil
Guest
 
Posts: n/a
Doze

Hey. Re:

"...But bear, as yet there's no evidence of a "wall of misunderstanding" in this accident because we don't have all the facts, yet you and many others (barely any of whom are current Airbus pilots) are pronouncing it as if you have the facts in your hands rather than simply regurgitating prejudice..."

Hmmm. "...to 13 degrees nose up, and remained in that position to impact..." (reference the THS via BEA note to Public.)

Perhaps then just a minor mistake? Someone did not get the a/c that "did everything it was supposed to do".. I call that evidence of a "Wall". If PF did not take note of the "THS MAN PITCH ONLY", I like to think that is a major misunderstanding. Why does the a/c "TRIM" outside NORMAL LAW?
Seems if the a/c was in need of emphatic inputs, perhaps "quickly needed" and in opposition to eachother, why invogorate a system that s l o w l y reacts with a gargantuan control surface, with immense authority, and likely to get in the way of assertive handling?

just a thought
 
Old 13th Jun 2011, 22:05
  #1943 (permalink)  
 
Join Date: Jul 2002
Location: UK
Posts: 3,093
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by rudderrudderrat
How do you cope with rudder trim?
Why would you be using rudder in cruise? Rudder is a different system anyway, and as I understand it is the most conventional aspect of FBW Airbus design.

@bearfoil : You've got no evidence for that assertion. You don't know, I don't know - none of us know what happened in that flight deck for those few minutes. We don't know whether the PF was confused by what he saw, we don't know if he panic-pulled (as has been known to happen) and we don't know if he did it because the little devil on his shoulder told him to. If you've got evidence that the pilot was confused by the law reversion then present it, otherwise you're just blowing hot air.
DozyWannabe is offline  
Old 13th Jun 2011, 22:14
  #1944 (permalink)  
bearfoil
Guest
 
Posts: n/a
Lonewolf

"...Remember: ACARS is a system intended to inform the manitenance shop what things were going wrong while the plane was flying, so they can have repair or replace options ready when the aircraft arrives at the next maintenance facility. The more I learn about it, the more useful I think it is for the paying customers. Faster turn around times and fewer things not working between stops could be a benefit of this system ... except of course for things that require major repair..."

Let's say I troubleshoot my aircraft aloft, and radio to Leo that xxx needs replacement, and I have two hours to layover on my way to Vegas. Leo says "Roj, bear, no big."

I own a GV and Leo pays his mortgage and buys a Corvette each year on 'my' dime. Pressure? uh, yep. Same with the Line, only worse. If I'm late, Leo deals with me, and he knows I will understand. On the ramp, Charlie has a poor record "keeping up" with Mx demands, because he is "old fashioned".

219 pax, a crew of twelve, all with Plans, and some are not so nice. ACARS is useful, but it is only a tool. Have you ever tried to show a beancounter how to use a tool?

bear

Dozy What I posted was evidence, from no less than BEA. You reply with three degrading possibilities for PF? Anything in your quiver that at least gives our Friend David a chance at saving his reputation? Because I know in my bones you think TRIMMING two barn doors is a good idea when you are about to die.
 
Old 13th Jun 2011, 22:25
  #1945 (permalink)  
 
Join Date: Jun 2009
Location: France
Age: 76
Posts: 196
Likes: 0
Received 1 Like on 1 Post
I suspect that the reason trim remains a sidestick function in Alternative Law would be in the case of an incapacitated crew scenario, where the remaining pilot has elevator and trim in their stick hand and throttles in the other, rather than having to dance between the stick, throttles and trim wheel with only two hands. What you're in effect proposing is a straight drop to Direct Law upon loss of air data.
I’m afraid the incapacitated crew scenario would be a rather weak justification for keeping auto-trim in ALT law. MS FS players all have joysticks with “Hat switches” that can be used to change trim. I would be surprised if military pilots ever used a trim wheel on their fbw jets.
DJ77 is offline  
Old 13th Jun 2011, 22:27
  #1946 (permalink)  
 
Join Date: Jun 2009
Location: I am where I am and that's all where I am.
Posts: 660
Likes: 0
Received 0 Likes on 0 Posts
rudderrudderrat - The important lesson to pull from the math is that the mass makes no difference in the physics class model.
Speaking of math - how does Mach .82 become something under 300 knots IAS when literature I can find suggests Mach 1 is over 580 knots? (585 knots at FL290 is the number from Wikipedia with an increase with altitude indicated by the three data points given.) I guess no effort is made to translate pitot tube indicated speed into a true speed through the air? Will this have to happen when laser speed measurement becomes practical?

Last edited by JD-EE; 13th Jun 2011 at 23:55.
JD-EE is offline  
Old 13th Jun 2011, 22:36
  #1947 (permalink)  
bearfoil
Guest
 
Posts: n/a
Trim is useless in upset. If fast enough to matter, it would be dangerous, and if slow enough to be safe, it is useless. And that's only if it stays put at 0 degrees.
 
Old 13th Jun 2011, 22:40
  #1948 (permalink)  
 
Join Date: Jul 2009
Location: Planet Earth
Posts: 91
Likes: 0
Received 0 Likes on 0 Posts
Originally posted by jcjeant:

Honestly I do not think the pitot had a fault
The pitot worked exactly as expected by their certification
They do not have a fault
They were used out of the domain of specifications and certification
It's exactly the same Airbus tell about their plane:
Our aircraft and systems worked as expected ..
The aircraft had no fault.
Of course if you go out of the certification specifications ... you can have some weird outcomes ....
More like "if you go out of the certification specifications ... you can have no weird outcomes"

Safety critical systems are designed to perform well beyond the certification specifications (as we now know from the survival of DFDR/CVR). Even in extreme cases like partial shutdown/reboot of systems, I'd bet Airbus fully understands the behavior of the system.

To the extent that Airbus thinks the a/c systems did not misbehave probably means that there are not going to be any surprises in future BEA reports.

Having said that, my reaction to A33Zab's image of Ecam view was: Yuck
CogSim is offline  
Old 13th Jun 2011, 22:41
  #1949 (permalink)  
 
Join Date: Jun 2009
Location: I am where I am and that's all where I am.
Posts: 660
Likes: 0
Received 0 Likes on 0 Posts
henra - remember I am a cynic when politics, lawyers, or marketing is involved.
I would invite you to make a case for any of the other involved people making the release with precisely the data given and no other data. It looks like the data benefits AirBus, is neutral to or damages Air France, and smears the pilots' reputations. It might have been the French government. Blaming the pilots gets them off a financial hook to some degree. Who else benefits?
JD-EE is offline  
Old 13th Jun 2011, 22:46
  #1950 (permalink)  
 
Join Date: Jul 2009
Location: UK
Posts: 134
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by JD-EE
...Speaking of math - how does Mach .82 become something under 300 knots IAS...
Its the speed that would give same dynamic pressure at standard air density (sea level) - useful because its basically what the wings use to generate lift, independent of altitude Its also basically what pitot tubes measure - think simple analogue dial without all the digital compensations! See also the definition of Flight Level FL and its link to real altitude in ft.
sensor_validation is offline  
Old 13th Jun 2011, 22:53
  #1951 (permalink)  
 
Join Date: Feb 2008
Location: In the Old Folks' Home
Posts: 420
Received 2 Likes on 1 Post
Are You A Pilot?

Dozy:
You're proposing a design change based on a single incident. Don't you think these scenarios have been played out to determine the design parameters? I suspect that the reason trim remains a sidestick function in Alternative Law would be in the case of an incapacitated crew scenario, where the remaining pilot has elevator and trim in their stick hand and throttles in the other, rather than having to dance between the stick, throttles and trim wheel with only two hands. What you're in effect proposing is a straight drop to Direct Law upon loss of air data.
Dozy, are you a pilot?
Smilin_Ed is offline  
Old 13th Jun 2011, 22:55
  #1952 (permalink)  
 
Join Date: Jul 2002
Location: UK
Posts: 3,093
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by bearfoil
You reply with three degrading possibilities for PF? Anything in your quiver that at least gives our Friend David a chance at saving his reputation? Because I know in my bones you think TRIMMING two barn doors is a good idea when you are about to die.
Incorrect. All I've said is that we don't know. I don't give a stuff about reputations (either corporate or personal), I want to stick to the facts, or at least to give everyone a fair hearing. The only way autotrim is activated is if the stick is fully deflected and held there past the elevator travel limit. It's there to give the pilot more authority when the chips are down. If your friend David wasn't aware of that then it was a failure in his training, not his piloting.

@DJ77. Doesn't sound that weak to me. If you've got full authority over the aircraft with both your hands on the primary flight controls then surely with the correct training it's an improvement? Just because cockpit ergonomics remained fairly static from the 1940s to 1988 doesn't mean that it's the "right" way to do it...

@Smilin_Ed - you should know I'm not (the clue's in the handle), nor have I ever pretended to be. You've got to understand that I'm not slamming the pilot because I don't have the evidence to do so (nor am I the kind of person who would even if I did). I'm just a little fed up with some on here bashing the aircraft and systems design when they don't have any evidence either.
DozyWannabe is offline  
Old 13th Jun 2011, 23:04
  #1953 (permalink)  
 
Join Date: Jun 2009
Location: I am where I am and that's all where I am.
Posts: 660
Likes: 0
Received 0 Likes on 0 Posts
GY, I am sure the substance of the BEA release is accurate as stated.

The cynic in me suggests it was to satisfy AirBus as AirBus leaked ever more data. It was finely crafted to really show only that the aircraft did exactly what the pilots told it to do. I can't see anything else the data shows conclusively. And it seems to have shut up the leak, AirBus or not AirBus.

I am sure the final report will show more than what the release shows. Do the aerodynamics of the aircraft support the altitude gain with a specific wind direction or still air? Does that shed light on anything in the cockpit? Was the data presented to the pilots sufficient for them to diagnose the situation in the face of a possible fixation on UAS procedures? Are there software improvements indicated? Are there flight display improvements indicated? Did Air France order a suitable set of options for the flight display? Are there hardware improvements indicated? Are there training improvements indicated?

These and more all must be answered in any final report. Some of it may end up showing AirBus in a bad light based on the total data set and serious aerodynamic modeling. And even if it shows AirBus in a bad light I suspect it will not contradict what was released. It will simply explain what was released.

The people here, mostly far more expert than I am, are discovering that the data shown reveals very little that can lead to a solid conclusion because we lack some of the data and the fine grain data from the recorder and the aircraft test and modeling efforts that the BEA no doubt has today. The important thing is that even as sloppy as this data may be - it shut up the leaks.

(And it gave us something to discuss here. I sure hope the final report addresses some of the issues we've found here well enough to satisfy us. We have found some potential issues in hardware, software, training, and design it seems. And one or more of these issues may still be unsolvable within the current state of the art.)
JD-EE is offline  
Old 13th Jun 2011, 23:07
  #1954 (permalink)  
bearfoil
Guest
 
Posts: n/a
Dozy

"...@DJ77. Doesn't sound that weak to me. If you've got full authority over the aircraft with both your hands on the primary flight controls then surely with the correct training it's an improvement? Just because cockpit ergonomics remained fairly static from the 1940s to 1988 doesn't mean that it's the "right" way to do it..."

Let me ask another way. Do you have full control of the aircraft with both hands and THS trimmed NU 13 degrees?

NO. Unless you have a third hand. The last thing anyone wants when trying to RECOVER, is an aircraft that is destabilized by something trying to HELP, that then quits
 
Old 13th Jun 2011, 23:12
  #1955 (permalink)  
 
Join Date: Jul 2002
Location: UK
Posts: 3,093
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by bearfoil
Let me ask another way. Do you have full control of the aircraft with both hands and THS trimmed NU 13 degrees?

NO. Unless you have a third hand. The last thing anyone wants when trying to RECOVER, is an aircraft that is destabilized by something trying to HELP, that then quits

capice?
Again there's no evidence for what you're asserting. Unless something went spectacularly wrong the only way the THS went up 13 degrees was because the PF put it there. Did something go spectacularly wrong with the systems or did the PF actually deliberately pull on the stick to get it into that position? Did he know that he could wind the trim forward with the wheel to remedy the situation? We don't know -which is why I want to wait until we know what happened before we start talking about changing features of the systems and aircraft design.
DozyWannabe is offline  
Old 13th Jun 2011, 23:13
  #1956 (permalink)  
 
Join Date: Jan 2005
Location: France
Posts: 2,315
Likes: 0
Received 0 Likes on 0 Posts
sensor_validation and JD-EE,
What's the argument?
ISA speed of sound at the altitude in question is in the order of 580 kts.
Mach 0.82 x 580 kts = 475 kts TAS
Do your sums for IAS.
ChristiaanJ is offline  
Old 13th Jun 2011, 23:17
  #1957 (permalink)  
 
Join Date: Aug 2009
Location: Texas
Age: 64
Posts: 7,197
Received 393 Likes on 244 Posts
bear, the nice thing about the ACARS is that a lot of trouble shooting can be set up that you can't trouble shoot or check for in the air. I spent a LOT of years writing up "gripes" in the maintenance office, describing what I was seeing in flight that was wrong. As time went on, I learned how to write a better gripe, and how to do a little trouble shooting, time permitting, before I landed, so I can give the mechanic more info when he enters his trouble shooting tree.

I see ACARS (in its role as maintenance and operations asset) as speeding up that process. If the pilot can add info, I am sure most companies call for them to do so, by voice, as you suggest you would do, and as I did for years.

"Chief, this is 231, we've got the fuel in manual trim. Looks like the normal actuator crapped out again ... " ah, the GE T-58, lovely kit.
Lonewolf_50 is offline  
Old 13th Jun 2011, 23:21
  #1958 (permalink)  
 
Join Date: Jun 2009
Location: VA, USA
Age: 58
Posts: 578
Received 0 Likes on 0 Posts
Speaking of math - how does Mach .82 become something under 300 knots IAS when literature I can find suggests Mach 1 is over 580 knots? (585 knots at FL290 is the number from Wikipedia with an increase with altitude indicated by the three data points given.) I guess no effort is made to translate pitot tube indicated speed into a true speed through the air? Will this have to happen when laser speed measurement becomes practical?
You can play with this (scroll down - there's a nice Mach/CAS/TAS calculator):

Aviation Calculator

0.82M = 279knots CAS @ FL350

Last edited by Jetdriver; 14th Jun 2011 at 03:15.
GarageYears is offline  
Old 13th Jun 2011, 23:21
  #1959 (permalink)  
 
Join Date: Feb 2008
Location: In the Old Folks' Home
Posts: 420
Received 2 Likes on 1 Post
Do You Have A Dog In This Fight?

Dozy, if you were a pilot you would understand why I, and some other pilots, don't want the trim to change by itself when we are trying to fly the airplane by hand. Due to reasons which are not yet clear to us on PPRuNE, the flight control system was not fully functional and it turned things over to the pilots, but not fully. Because of what may have been an inadvertent nose-up input to the side stick, the trim went full up and the airplane was trimmed into a stall from which the pilots were not able to recover.

When practicing stalls, student pilots are warned NOT to trim into the stall. That is so when they let go of the stick, the airplane will return to a trimmed speed which is BELOW the stall speed. Further, if you trim into the stall, the trim might not move fast enough to get you out when you need it to. I suspect that these guys were blindsided by the autotrim.

Next question: Were you involved in the design of the FBW system under discussion?
Smilin_Ed is offline  
Old 13th Jun 2011, 23:22
  #1960 (permalink)  
 
Join Date: Aug 2009
Location: Texas
Age: 64
Posts: 7,197
Received 393 Likes on 244 Posts
JD

IIRC from my wiz wheel days ...

Indicated to (check the card/chart in the aircraft) Calibrated to (adjust for temp and altitude (air density) True. IIRC, the Higher you go, the more True you get for a given Indicated/Calibrated (those tend to be close).

You then vector sum your wind component with your velocity (a vector) (True Airspeed & heading) to get your Ground speed and Track. (Another vector, a resultant IIRC).

GPS uses expensive gremlins to do all that.

Cheers.
Lonewolf_50 is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.