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

AF447

Old 15th Aug 2009, 10:01
  #4241 (permalink)  
 
Join Date: Jul 2000
Posts: 441
Likes: 0
Received 0 Likes on 0 Posts
Captplaystation, mate I completely agree with you!

I fly the A332 (and A343/5), so I am obviously keen to find out what happened, however the thought of wading through 4000 posts of speculative drivel (as is often the case on these hallowed forums) fills me with dread and fear, and frankly I can't be arsed!

So please guys, why don't we make a new pact (or thread) that only brings NEW relevant information to the fore that actually may be of some use to us buggers that actually fly the things.

Cheers
Oblaaspop is offline  
Old 15th Aug 2009, 13:17
  #4242 (permalink)  
 
Join Date: Feb 2009
Location: Virginia
Posts: 1,796
Likes: 0
Received 9 Likes on 8 Posts
Seems to me there's a big difference between speculating on other possible scenarios and saying flat-out that the preliminary report's wrong.

If the galley tumbled down by itself, it's an interesting coincidence that it landed right-side up (as the damage at the bottom seems to indicate). Add in the similiar damage pattern on a number of other items, and coincidence starts looking like a pretty unsatisfactory explanation.
Chu Chu is offline  
Old 15th Aug 2009, 14:11
  #4243 (permalink)  
 
Join Date: Jun 1997
Location: 5530N
Posts: 845
Likes: 0
Received 0 Likes on 0 Posts
i reckon the final report will say a perfectly serviceable aircraft entered an area of extreme intense thunder storm activity supplemented by abnormally high ISA's being a contributory factor.
Bearcat is offline  
Old 15th Aug 2009, 23:36
  #4244 (permalink)  
 
Join Date: Jan 2002
Location: USA
Posts: 286
Likes: 0
Received 0 Likes on 0 Posts
Why is anybody so quick to close this topic. If you frequent the thread then it takes very little time to keep and stay up to date. If a poster is being redundent with previous info, simply disregard it and continue to the next post. Suggesting the topic be closed is a redundent statement too.
wes_wall is offline  
Old 17th Aug 2009, 01:04
  #4245 (permalink)  
 
Join Date: Jul 2009
Location: Not far from a big Lake
Age: 81
Posts: 1,461
Likes: 0
Received 0 Likes on 0 Posts
Pitot failure modes

Ok, quick question. If you ice over the pitot tube inlet, the obvious thing that should happen is that the pressure in the tubing behind the pitot will bleed out the bleed port intended to remove moisture and airspeed indications will drop toward zero.
But on a heated pitot, if the interior is hot enough, some of the moisture might flash to steam and actually pressurize the pitot system between the ice block and the remaining tubing. Has anyone seen this effect? Keep in mind that the boiling point of water at FL350 isn't that high. Much less than 100 degrees C/ 212 degrees F.
Can anyone conclusively say that AF447 didn't get a (bogus) Mach warning at the beginning of their problems?
Sid
Machinbird is offline  
Old 17th Aug 2009, 11:10
  #4246 (permalink)  
Nightrider
Guest
 
Posts: n/a
Boiling point of water at 11,000 mtrs is around 31 deg C.
 
Old 17th Aug 2009, 12:46
  #4247 (permalink)  
 
Join Date: Jan 2008
Location: Manchester UK
Age: 79
Posts: 9
Likes: 0
Received 0 Likes on 0 Posts
I would imagine that the latent heat of vaporisation at 31C would be very different to the usually quoted value at 100C. Just goies to show why youy can't get a decent cup of coffee up a mountain.
Dr Brian Evans is offline  
Old 17th Aug 2009, 14:45
  #4248 (permalink)  
 
Join Date: Jun 2001
Location: UK.
Posts: 4,391
Likes: 0
Received 0 Likes on 0 Posts
Elevation Water boiling Temp. Latent heat of vapourisation
MSL...........212F 100C.................970 Btu/lb
36,000 ft....145F 63C.................1010 Btu/lb

Not sure what significant effect the latent heat of vapourisation has.
Basil is offline  
Old 17th Aug 2009, 15:04
  #4249 (permalink)  
 
Join Date: Apr 2002
Location: Surrey, UK ;
Age: 70
Posts: 1,142
Received 4 Likes on 4 Posts
Not adding anything to the debate, other then to prove there are more answers than question on the web .. this is a different set of numbers from wiki-answers.

17 in. Hg: 188.07 F or 86.71 C (at approx 15,000 ft or 4572 m above SL)

10 in. Hg: 175.11 F or 79.51 C (at approx 27,000 ft or 8230 m above SL)

5 in. Hg: 165.85 F or 74.36 C (at approx 42,000 ft 12,802 m above SL)

Perhaps when I get a minute tomorrow I'll find the formaula and make an excel sheet .. if only for me own eddification. Then look up what latent heat of vaporisation has to do with it - and why it increases at altitude, when I would expect it to decrease with falling vapour pressure.

DGG
Dave Gittins is offline  
Old 17th Aug 2009, 16:03
  #4250 (permalink)  
 
Join Date: Aug 2003
Location: FR
Posts: 227
Likes: 0
Received 0 Likes on 0 Posts
A quick question to AF crew, if they happen to read this. Do you get any information about the search operations? The latest summary I found on the BEA site is from July 17th. If you have information, are you allowed to share it? I'd like to know what area has been surveyed so far; what the planning is; is the progress as foreseen, or slower?
pax2908 is offline  
Old 18th Aug 2009, 08:08
  #4251 (permalink)  
 
Join Date: Jun 2001
Location: UK.
Posts: 4,391
Likes: 0
Received 0 Likes on 0 Posts
Dave,
Then look up what latent heat of vaporisation has to do with it - and why it increases at altitude, when I would expect it to decrease with falling vapour pressure.
Again, not terribly relevant but, at a saturated steam pressure of 3208psi (705F) the latent heat of vapourisation is zero. Not many people know that

Re your boiling points, my Callendar Steam Tables seem to disagree. They're psi/Btu/lb/deg F so perhaps I've got a conversion wrong.
How's that for thread creep? - from an advanced FBW aircraft to a 1960 steam turbine engine room.

Last edited by Basil; 18th Aug 2009 at 08:26.
Basil is offline  
Old 18th Aug 2009, 12:02
  #4252 (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
Machinbird, you commented, " Keep in mind that the boiling point of water at FL350 isn't that high. Much less than 100 degrees C/ 212 degrees F."

Is this the right observation. What is the pressure IN the pitot-tube and the tubing up to the ADIRU? (And, for that matter, what is the temperature of the probe and of the tubing up to the ADIRU?)

JD-EE
JD-EE is offline  
Old 18th Aug 2009, 13:51
  #4253 (permalink)  
 
Join Date: Nov 2006
Location: SoCalif
Posts: 896
Likes: 0
Received 0 Likes on 0 Posts
Back to EE School for You, JD

Sorry, couldn't resist.

There are Air Data Modules between the pitot and the ADIRU, presumably very close to the pitot. Sorry, don't remember their exact names, and it's a long ways back to find the block diagram.

Still, you point is taken that the boiling point would vary with impact pressure, i.e., airspeed, but only by an inch or so of Hg.

GB
Graybeard is offline  
Old 18th Aug 2009, 17:42
  #4254 (permalink)  
 
Join Date: Jul 2009
Location: Not far from a big Lake
Age: 81
Posts: 1,461
Likes: 0
Received 0 Likes on 0 Posts
JD-EE, The point was made to show there is more than one type of potentially erroneous output from a pitot tube. If the interior of the pitot tube is hot enough to flash fresh moisture to steam (and it doesn't need to be that hot) then you could see your airspeed indications going up instead of down after the first hail stone plugs up your pitot tube inlet.
Perhaps this type of thing accounts for the apparent difference between Thales and Goodrich probes.
How should you react to an initial mach alarm after flying into the top of a storm?
Would you just say its bogus, or begin reducing power? And then if all your airspeed indications packed up and everything associated with it downstream (like ADIRUs) began quitting, would you even remember you had just pulled a bit of power? Would you even be able to read your power setting in the turbulence?
Machinbird is offline  
Old 19th Aug 2009, 05:11
  #4255 (permalink)  
PBL
 
Join Date: Sep 2000
Location: Bielefeld, Germany
Posts: 955
Likes: 0
Received 0 Likes on 0 Posts
Important Information on Pitot Problems

I don't generally contribute any more, but I think this is important information.

There is a superb piece by Jens Flottau in Aviation Week for August 10, 2009 detailing what was known about high-altitude (e.g., FL 350) extra-cold (-50C and below) pitot icing on A330/340 aircraft before June 1, 2009. The answer is: lots.

In my opinion this is prize-winning research and writing. It hasn't been mentioned here up to now, AFAIK.

Response to Airbus Pitot Tube Incidents Under Scrutiny | AVIATION WEEK

PBL
PBL is offline  
Old 19th Aug 2009, 07:45
  #4256 (permalink)  
 
Join Date: Dec 2001
Location: England
Posts: 1,389
Likes: 0
Received 0 Likes on 0 Posts
Are any companies leaving one Thales probe on or are they replacing all three? Leaving one might allow useful data to be collected?
cwatters is offline  
Old 19th Aug 2009, 12:44
  #4257 (permalink)  
 
Join Date: Mar 2002
Location: Florida
Posts: 4,569
Likes: 0
Received 0 Likes on 0 Posts
cwatters

Are any companies leaving one Thales probe on or are they replacing all three? Leaving one might allow useful data to be collected?
from the link in the post above yours

EASA stopped short of banning the Thales probes outright, allowing operators to continue to use the so-called -BA standard as a third sensor on Airbus widebodies. A regulatory official says continued use of one Thales -BA probe is "probably acceptable."
lomapaseo is offline  
Old 19th Aug 2009, 13:09
  #4258 (permalink)  
 
Join Date: Mar 2002
Location: Florida
Posts: 4,569
Likes: 0
Received 0 Likes on 0 Posts
The safety related response to all this is discussed briefly in the "piece by Jens Flottau in Aviation Week for August 10, 2009. "

A speed sensing malfunction for any reason was probably judged during initial certification as a minor malfunction due to its low expected rate of occurrence as well as the barriers (crew actions and availability of other instruments) available to make it unlikely that it would progress to a more serious outcome.

The article mentioned above indicates that the additional in-service experience reveals that the frequency of the malfunctions coupled together with the likelihood of significantly increasing pilot workload now creates a more hazardous outcome which needs to be addressed. Somewhat akin to the engine grapple (ice Crystals) problems discussed in the past when aircraft flew over storms.

The challenges to addressing problems like are also similar. If you go for a simple product change like a different manufactured probe the question is immediately how much is good enough and how do you know? Since the original product meets the certification standards.

Other means of addressing the safety risk are avoidance as well as means for reducing the pilot workload (simplified tasks by memory). Again the issue is a practical way for doing this (retraining all pilots takes time).

Right now it looks like a combination will be tried in a subjective manner to at least add more data to the knowledge base. I'm not sure if this gets mandated by EASA or not or even if the FAA will follow.
lomapaseo is offline  
Old 19th Aug 2009, 15:55
  #4259 (permalink)  
 
Join Date: Jun 2009
Location: Bedford, UK
Age: 69
Posts: 1,328
Likes: 0
Received 0 Likes on 0 Posts
PBL: thanks for the link

..however I am not sure what to make of this text:

'Since the crash of Flight 447, EASA and Airbus have reminded operators of the need to ensure that pilots are skilled in techniques to maintain level flight.'

Any insight of what this statement really means and how operators have reacted to it ?
Mr Optimistic is offline  
Old 19th Aug 2009, 16:20
  #4260 (permalink)  
 
Join Date: Jul 2009
Location: USA
Posts: 102
Likes: 0
Received 0 Likes on 0 Posts
...interesting article from Aviation Week

What manufacturer does Boeing use for its pitot tubes?
robertbartsch is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell or Share My Personal Information

Copyright © 2023 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.