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Brand new Etihad A340-600 damaged in Toulouse; several wounded

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Brand new Etihad A340-600 damaged in Toulouse; several wounded

Old 21st Nov 2007, 20:12
  #201 (permalink)  
 
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What Joetom is saying; if a tyre is pushing against a normal angled chock then it's trying to lift from the ground. If it does ...............

( Correct me if I'm wrong Joetom. )
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Old 21st Nov 2007, 20:15
  #202 (permalink)  
 
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Chox??? Chocks!

Also to note, during Engine runs, Chox should be a little distance from tyres, touching the tyres has caused many aircraft to move.
Utter BOWLARKS!!
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Old 21st Nov 2007, 20:16
  #203 (permalink)  
 
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How to shut down engines, they need fuel,air and fire...Once they are running they can be the devil to stop. The simplest method is to turn off the fuel which is exactly what we airframe drivers do. If its a wreck then get off panel at the fcu and turn it off manually (did this personally once on a B105 wreck in a tree) dont ask - obviously fire crews would need some tech help. At an Air Force Base where I was based we used to have the fire guys around and showed them. On smaller engines PT 6 etc you can also kink the fuel line - on the big boys hmmm, I dont know so much. Spraying stuff in at the front end might just result in a very shiny clean compressor section...
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Old 21st Nov 2007, 20:17
  #204 (permalink)  
 
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Post 42 - the ac had completed the engine trials and was exiting the test bay!
Who to believe now!
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Old 21st Nov 2007, 20:34
  #205 (permalink)  
 
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Utter BOWLARKS!!
TURIN, If you can't see the simple physics involved in this picture then I'd suggest you stay in the hangar - or crew room.
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Old 21st Nov 2007, 20:47
  #206 (permalink)  
 
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from the latest flight report...re the dgac enquiry am I to presume the biggest clowns in history were innvoled in this run up....thats eveyone included in the test.


I feel a mod's axe forth coming. The truth some times hurts.
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Old 21st Nov 2007, 20:49
  #207 (permalink)  
 
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Forget, I have read some of your earlier posts. You should stay in your institution!

If the chocks are not hard against the tyres then they can be pushed away.
If they are hard against the rubber you're going nowhere.

Risk assesments and ramp experience prove it.

Of course this has nothing to do with this case as apparently they were not in place.
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Old 21st Nov 2007, 21:26
  #208 (permalink)  
 
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Since there was no fire... maybe just let the engines get rid of the remaining fuel?
While dealing with the injured crew?

They did empty a few fire tenders worth of foam around the aircraft, judging by the photos.
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Old 21st Nov 2007, 22:30
  #209 (permalink)  
 
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If Chox are placed next to tyres, during Mod or Hi powered eng runs, they tend to allow the base of the tyres to reduce contact with the surface on the ground and will allow the aircraft to move.
.
Best option during hi-powered eng runs is big chox placed a few inches infront of tyres and a person outside and inside the aircraft looking to see if aircraft is moving, if aircraft moves they should advise person in control of engines to reduce power.
.
All very simple.
.
Chox use has reduced over the years, expect more of the above.
.
Cheers.......
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Old 22nd Nov 2007, 00:11
  #210 (permalink)  
 
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About chocks reducing effective holding power:

Warning: a light-weight pilot contribution
Doesn't it simply depend on the size and material of the said chocks?
If the wheels are so in touch with the chocks that they lean on them under power, then they transfer some of the aircraft weight to the tarmac via said chocks, and the contact area of the chocks as well as their coefficient of friction with respect to the tarmac will start to matter. If they are made of aluminium, for example, then the holding ability of the tire will probably suffer, as together they will slide along the asphalt / concrete.
Such chocks should still be somewhat useful when brakes fail and the wheel is free to roll, me thinks, so placing them a bit of a distance from the wheels would make sense.
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Old 22nd Nov 2007, 01:24
  #211 (permalink)  
 
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If nothing else, if the tire (sorry, tyre ) rolls over the chock, there's a noticeable bump that may alert the crew that the aircraft is no longer stationary.
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Old 22nd Nov 2007, 01:30
  #212 (permalink)  
 
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quote below is from the Maintenance Manual. (a 747 manual, but you get the picture)
My highlighting.


C. Prepare for Engine Operation
(1) Check that airplane is parked in clean area with wheels on areas
that are free of oil, grease, or other slippery substances.

(2) Make sure the wheel chocks are installed at the main landing gear
wheels and ground locks are installed.

(a) Do these steps if you will operate the engines for a high power
engine run.

1) Make sure that the forward wheel chock is six to twelve
inches in front of the tires.
NOTE: This will cause the thrust of the engine to be held
by the frictional force between the airplane tires
and the ground, and not the wheel chock. The wheel
chocks do not have the same frictional force as the
tires. If the tires touch the wheel chock, some of
the frictional force between the tires and the
ground is lost, and the airplane can skid. The
wheel chocks are only used to prevent the airplane
from rolling if the airplane brakes were
accidentally released before or after the engine
run.
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Old 22nd Nov 2007, 02:46
  #213 (permalink)  
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1) Make sure that the forward wheel chock is six to twelve
inches in front of the tires.
NOTE: This will cause the thrust of the engine to be held
by the frictional force between the airplane tires
and the ground, and not the wheel chock. The wheel
chocks do not have the same frictional force as the
tires. If the tires touch the wheel chock, some of
the frictional force between the tires and the
ground is lost, and the airplane can skid. The
wheel chocks are only used to prevent the airplane
from rolling if the airplane brakes were
accidentally released before or after the engine
run.
Ah, PPRune, always an educational experience!
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Old 22nd Nov 2007, 07:00
  #214 (permalink)  
 
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Forget, I have read some of your earlier posts. You should stay in your institution!
How exceedingly satisfying.

Take Note TURIN, and get back to the crew room.

Risk assesments and ramp experience prove it.


Owe you one Spanner Turner.
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Old 22nd Nov 2007, 07:11
  #215 (permalink)  
 
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Ok... of course I stand to be shot down because I wasn't there and shouldn't judge. I am not judging, simply asking a question:

Would any pilot feel particularly comfortable doing engine runs relying on the park brake? From experience, I would prefer to hold main brake pressure instead of relying on the park brake, and would guard the thrust levers at all times, ready to retard.

11 seconds elapsed between the first sign of aircraft movement and retardation of the thrust levers.

Not sure if the 'commander' was a ground engineer or a pilot, but as a pilot I would try to avoid 'heads down' time if I was in control of the aircraft during an engine run. Let someone else look at the instruments...

Are ground engineers encouraged to display similar caution?

VI
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Old 22nd Nov 2007, 09:35
  #216 (permalink)  
 
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Spanner Turner,

thanks, that's very interesting.

That also means that chocks are no safety measure for engine run-ups, but merely to secure a parked aircraft. They're only designed to keep an unbraked aircraft from rolling away by gravity (downhill) or (perhaps) idle thrust, if the parking brake fails.

Since apparently high power was still applied on all engines, it follows that chocks would not have prevented this accident. If they reduce friction when pushed against, they might even have exacerbated it.

Makes me wonder if there are specially designed chocks (perhaps with rubber "feet") made to hold an aircraft against high engine power?

As to the parking brake: istr that for (at least CFM-equipped) A320 it is not advised to power up the engines beyond 75% N1 with the parking brake on. I imagine there's a similar limit for A340.


Bernd

Last edited by bsieker; 22nd Nov 2007 at 10:03. Reason: grammar
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Old 22nd Nov 2007, 09:44
  #217 (permalink)  
 
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Would you listen to some of you? No wonder there's never going to be a pilot only forum on here. I would hazard a guess that less than 0.1% of all airline pilots have EVER performed high power ground run tests of engines. It's an an engineering function not a pilot function.

So, here we have some of the so called 'expert pilots' giving us the benefit of their engine ground run experience which amounts to about the same as a gnats fart! The next thing is we have them telling us about how to chock the a/c. Thanks to an engineer who took the time to take the relevant bit out of Boeing's engineering manual.

Whilst this incident is sad for the injuries and the loss of an airframe, it has NOTHING to do with pilots or piloting. Yet, here we have a huge thread full of inane drivel and highly speculative pomposity about how it should have been done from the mouths of sad people who are either pilots with absolutely no experience of conducting high power, static, engine ground runs or else just anoraks who think they know everything because they have completed half their spotters handbook of registrations!

What we have here is some engineers and technicians messing up big time. That's it. End of story. But nooo... the anoraks have to start telling the rest of us how they would have conducted it and what they did wrong in Tolouse when in fact, the sum total of their experience in these things is ZERO.
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Old 22nd Nov 2007, 09:50
  #218 (permalink)  
 
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An Apology

I humbly bow to the PPRuNe great and good for putting a miserable old fart such as myself firmly in his over inflated place.
forget, joetem etc. I apologise profoundly.
Will thrash myself with a birch for the rest of the week.

mumbo jumbo
The next thing is we have them (pilots) telling us about how to chock the a/c.
If that is referring to me I resent the remark as I'm not a pilot. (Which when I think about it makes my load of old bowlarks look even worse).

Last edited by TURIN; 22nd Nov 2007 at 09:54. Reason: mumbo jumbo
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Old 22nd Nov 2007, 10:40
  #219 (permalink)  
 
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Chocks used

The company I work for have specially made chocks, we park the wheels of the A/C on top of these and the combination of the A/C weight and forward force during engine runs ensure no movement. I might add that these chocks are about 500 mm in height.
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Old 22nd Nov 2007, 12:13
  #220 (permalink)  
 
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But do they still rely on static friction with the tarmac? Go back and read Physics 101 about static friction coefficient - it is independent of the friction surface area.

While visiting Edwards AFB a few decades back, I witnessed a static runup with the bird harnessed to a massive anchor (with a straingaged link for thrust measurement BTW). That test wasn't going ANYWHERE.
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