Search the archive:
 YaBB - Yet another Bulletin Board
 
   
 
  Simviation Forum › Real World › Real Aviation › Rio flight missing?
(Moderators: Mitch., Fly2e, ozzy72, beaky, Clipper, JBaymore, Bob70, BigTruck)
‹ Previous Topic | Next Topic ›
Pages: 1 2 3 4 
Send Topic Print
Rio flight missing? (Read 1653 times)
Reply #45 - Jun 11th, 2009 at 12:44pm

Hagar   Offline
Colonel
My Spitfire Girl
Costa Geriatrica

Posts: 33159
 *****
 
expat wrote on Jun 11th, 2009 at 6:34am:
Hagar wrote on Jun 11th, 2009 at 4:43am:
I'm not convinced that's peculiar to Airbus Matt. Most aircraft will automatically recover from a stall if left alone. I always understood that aerodynamics plays very little part with this type of aircraft. I remember the impressive demonstrations of the Airbus at Farnborough at an extreme alpha angle when a conventionally controlled aircraft would have fallen out of the sky. http://www.youtube.com/watch?v=0jz957KRXzQ

In your example would not the computer attempt to correct the nose-down attitude by applying up elevator? This would be the normal reaction of a human pilot in a conventional aircraft in similar circumstances & would make the situation worse.

What's always worried me about 'fly-by-wire' systems is whether it's possible for the crew to override the computer or even have any control at all in the event of a catastrophic electrical failure. When the whole system relies on a simple component like a pitot tube did they ever think to have a backup of a different type in case it goes wrong? A chain is as strong as its weakest link.

Pitot tubes are fitted to all types of aircraft & have worked reliably for many years so what's different about the ones used by Airbus?



That is the whole idea behind this aerodynamic design. If the entire fly by wire system failed then the aircraft can be flown by differential thrust alone. We have seen with for example with the Soux City crash that it was possible with a DC 10, but it is designed into the Air Bus not to be possible, but to be able to do it. This is one of the reasons why the flying control surfaces are aerodynamically neutral. Without power, they droop on the ground, but in the air without power they go naturally neutral with the airflow and cannot freeze in an up or down position. Can the pilot over rule, the answer is a big NO! Against this, outside of one very public accident, when have the computers got it wrong agaist the rather large number of pilot error accidents? As for the pitot tubes going tits up, for start there is not just one. The pilot has one, the co-pilot has one and then they have a standby. It cannot boil down to just a pitot failure. The right and left systems are separate as is the standby system. What is common to the three systems is pitot heating, but even that has different channels. Without the CDR and CVR it is just speculation and window dressing by anyone who decides to replace fleet wide pitot tubes.

Matt

Thanks for clearing that up Matt. However, are not the engines controlled by the same fly-by-wire system? If the whole system failed through lack of power I don't see how any of this could help.

If the reports are correct & the aircraft was in a storm with severe turbulence then normal aerodynamic theory goes out of the window. There has been a lot of speculation that the speed sensors (pitot tubes) contributed to the disaster. I don't know how true this is or where they got the information but Air France have confirmed that these were due to be replaced on their whole fleet of A330s in accordance with a manufacturer's service bulletin. While this was not mandatory it indicates that there was a known fault with the original components.

I also couldn't understand why the Brazilian government has been insistent from the beginning that terrorism was not involved. I'm usually critical of the media for blaming everything on terrorists but in this sort of situation nothing should be ruled out.
 
...

Founder & Sole Member - Grumpy's Over the Hill Club for Veteran Virtual Aviators
Member of the Fox Four Group

Need help? Try Grumpy's Lair

My photo gallery
Back to top 
IP Logged
 
Reply #46 - Jun 11th, 2009 at 3:49pm

expat   Offline
Colonel
Deep behind enemy lines!

Gender: male
 Posts: 8499
 *****
 
Hagar wrote on Jun 11th, 2009 at 12:44pm:
expat wrote on Jun 11th, 2009 at 6:34am:
Hagar wrote on Jun 11th, 2009 at 4:43am:
I'm not convinced that's peculiar to Airbus Matt. Most aircraft will automatically recover from a stall if left alone. I always understood that aerodynamics plays very little part with this type of aircraft. I remember the impressive demonstrations of the Airbus at Farnborough at an extreme alpha angle when a conventionally controlled aircraft would have fallen out of the sky. http://www.youtube.com/watch?v=0jz957KRXzQ

In your example would not the computer attempt to correct the nose-down attitude by applying up elevator? This would be the normal reaction of a human pilot in a conventional aircraft in similar circumstances & would make the situation worse.

What's always worried me about 'fly-by-wire' systems is whether it's possible for the crew to override the computer or even have any control at all in the event of a catastrophic electrical failure. When the whole system relies on a simple component like a pitot tube did they ever think to have a backup of a different type in case it goes wrong? A chain is as strong as its weakest link.

Pitot tubes are fitted to all types of aircraft & have worked reliably for many years so what's different about the ones used by Airbus?



That is the whole idea behind this aerodynamic design. If the entire fly by wire system failed then the aircraft can be flown by differential thrust alone. We have seen with for example with the Soux City crash that it was possible with a DC 10, but it is designed into the Air Bus not to be possible, but to be able to do it. This is one of the reasons why the flying control surfaces are aerodynamically neutral. Without power, they droop on the ground, but in the air without power they go naturally neutral with the airflow and cannot freeze in an up or down position. Can the pilot over rule, the answer is a big NO! Against this, outside of one very public accident, when have the computers got it wrong agaist the rather large number of pilot error accidents? As for the pitot tubes going tits up, for start there is not just one. The pilot has one, the co-pilot has one and then they have a standby. It cannot boil down to just a pitot failure. The right and left systems are separate as is the standby system. What is common to the three systems is pitot heating, but even that has different channels. Without the CDR and CVR it is just speculation and window dressing by anyone who decides to replace fleet wide pitot tubes.

Matt

Thanks for clearing that up Matt. However, are not the engines controlled by the same fly-by-wire system? If the whole system failed through lack of power I don't see how any of this could help.

If the reports are correct & the aircraft was in a storm with severe turbulence then normal aerodynamic theory goes out of the window. There has been a lot of speculation that the speed sensors (pitot tubes) contributed to the disaster. I don't know how true this is or where they got the information but Air France have confirmed that these were due to be replaced on their whole fleet of A330s in accordance with a manufacturer's service bulletin. While this was not mandatory it indicates that there was a known fault with the original components.

I also couldn't understand why the Brazilian government has been insistent from the beginning that terrorism was not involved. I'm usually critical of the media for blaming everything on terrorists but in this sort of situation nothing should be ruled out.


As I said with the pitot probe replacement, I think it is just window dressing, keeps the punters happy. Without the CDR and CVR it is pissing in the dark and hoping you will hit the bowl. As to the engine question, that is a common misconception with fly by wire. A FADEC (full authority digital engine control) is not part of the fly by wire system. It is an electric system, but it has nothing to do with the fly by wire system. It is a totally separate entity. It is a bit like saying the landing lights and the cabin lights are the same thing, yes they are both lights, but that is where the similarity ends. The FADEC has a completely isolated power supply and if that power supply is lost or interrupted then the engines take over. Each engine has an dedicated and completely independent AC generator running off said engines own accessory gearbox that when power is lost will supply power directly to the FADEC and no other system. This generator can power the FADEC for an entire flight without problem. Rather ironic, that as this Air Bus broke up in the sky, the engine control would have been 100% functional right up until the fuel supply was lost and the engine wound down due to said destruction.

Matt
 
PETA ... People Eating Tasty Animals.

B1 Boeing 737-800 and Dash8 Q-400
Back to top 
IP Logged
 
Pages: 1 2 3 4 
Send Topic Print
‹ Previous Topic | Next Topic ›
  « Home ‹ Board Top of this page

Simviation Forum » Powered by YaBB 2.5 AE!
YaBB Forum Software © 2000-2010. All Rights Reserved.

Valid RSS Valid XHTML Valid CSS Powered by Perl Source Forge