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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 22nd Nov 2007, 12:13
  #221 (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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Old 22nd Nov 2007, 12:53
  #222 (permalink)  
 
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Mumbo,

Not sure where you're post was aimed at, but I'll bite at a couple of concepts contained therein:

* Those pilots commenting here about their experience conducting ground runs may not necessarily be airline pilots. I agree that if they were they would almost certainly have very slim experience. Believe it or not - in some organisations, the pilots are most certainly present (and interested!) in such testing. The concepts are the same on an A340 or something 1/2 or 1/10 the size. F=MA...

*
Whilst this incident is sad for the injuries and the loss of an airframe, it has NOTHING to do with pilots or piloting.
Sorry mate, but I reckon you're about 1000 miles down the wrong track with that opinion. Engineers are obviously indispensable to a safe and successful aviation operation, but your comment regarding pilots was either deliberately or unknowingly arrogant and unintelligent. Who flies the bloody things?

What we have here is some engineers and technicians messing up big time.
No sh*t mate!

I wasn't out to criticise, merely float some ideas. Many aircraft have crashed into the ground over the years through crew preoccupation/distraction with stuff other than what's happening outside the aeroplane. Through years of education and cultural change, the statistics have improved immensely.

Stuff like this happens. Unfortunate but true. Open communication and discussion on these issues may prevent someone like you screwing up one day - but only if you can swallow your engineer ego for a moment and listen...

VI
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Old 22nd Nov 2007, 14:19
  #223 (permalink)  
 
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This thread has twisted around so much that I can't discern fact from opinion.

I'm still trying to figure out what procedures were being used vs what procedures were recommended by Airbus.

I presume that what is recommended and published is based on sound engineering principals and years of experience, so I'm still trying to read beyond any opinions that do not quote these exact procedures for this aircraft in a specified ground run test.

So, is this a judgemental problem associated with a lack of awareness in the cockpit, or is it a problem associated with bypassing a procedure? I tend to supspect the former based on the delay in applying braking action.
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Old 22nd Nov 2007, 14:51
  #224 (permalink)  
 
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an interesting article in the dutch media reported, the French test pilots failed the brake in time.
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Old 22nd Nov 2007, 16:02
  #225 (permalink)  
 
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Lomapaseo,
So far I don't think there is anything much known yet about who did what. With people still in hospital at the moment, I would expect they will take their time to piece the story together before making statements.

Tediek,
Read post #193.
Airbus themselves say they were on the pedal brakes almost immediately, but took a long time before closing the throttles.

I expect the Dutch media are just like the rest, you cannot even trust them as far as you can throw a crumpled newspaper.
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Old 22nd Nov 2007, 16:19
  #226 (permalink)  
 
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I doubt that using brake pedals instead of parking break would have had any effect. The wheels were probably not turning anyway, but were being pushed on the concrete. So the only thing that matters for acceleration is the friction between the rubber and the concrete and the thrust of the engines.
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Old 22nd Nov 2007, 17:05
  #227 (permalink)  
 
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Profit Max,
Please... we do NOT know yet "who" did "what".
Of course we can now switch to endless speculation on what happened, like with the Congonhas, Brazil A320 crash (remember the number of pages that generated?).

Like we can speculate endlessly on how the people in charge interpreted the aircraft moving as a parking brake failure. So they stood on the brake pedals. Took a few seconds to realise that didn't work either, so their diagnose was wrong. By the time somebody changed his mind and chopped the throttles, they were at 30 kts.

It's hardly as if it were a day-to-day issue for the average pilot. How many here on the forum do pre-delivery engine runs for a living?

So let's hold off, until the guys in hospital have had a chance to have their say.
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Old 22nd Nov 2007, 17:19
  #228 (permalink)  
 
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Originally Posted by ChristiaanJ
Please... we do NOT know yet "who" did "what".
Where did I say anything like that?

I purely stated that switching to the pedals would have no effect on stopping the aircraft as the wheels would be skidding anyway, and not turning. That the switching to pedals happened is based on the Airbus memo quoted earlier, the only real factual information we have anyway.
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Old 22nd Nov 2007, 17:42
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Profit Max,
Where did I say anything like that?
My sincere apologies. You did not.
And since we still don't know why the aircraft started to move in the first place, even my "hypothetical speculation" is out of place.
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Old 22nd Nov 2007, 18:20
  #230 (permalink)  
 
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I totally agree with Profit Max. Those wheels would not have been turning but skidding along the concrete. Doesnt make a difference it was park brake or the pedals.
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Old 22nd Nov 2007, 18:45
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Thank you for the explanation from the Boeing manual. I didn't understand the "not touching" bit, as the last full power test i saw was this one a couple of months ago:
http://www.draken.dk/index.htm
The chocks are larger than normal "parking" ones, almost vertical, definitely touching the tires and chained.
Best regards
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Old 22nd Nov 2007, 23:40
  #232 (permalink)  
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magicE, profitmax;

Those wheels would not have been turning but skidding along the concrete. Doesnt make a difference it was park brake or the pedals.
Not quite correct.

The park brake applies pressure only to the main gear and not the center gear, (except when the ground spoilers are deployed where, in an emergency (assumed to be on the runway), park-brake application will set all wheel brakes including those on the center gear).

The brake pedals apply wheel and center gear brake pressure. The left pedal applies left main brakes plus forward center gear brakes, the right pedal applies right main brakes plus aft center gear brakes.

Anti-skid braking is available on all wheel brakes, (mains and centers), above 10kts groundspeed, and, with heavy braking only, below 10kts. Anti-skid is obviously not available on the park brake.

Given this, the main and center gear wheels would be turning even under maximum pedal deflection, just above the skid point. On-site, there would be signs of heavy braking if indeed it was applied through the pedals, but there would not be skidding.

If the park brake remained set throughout the accident sequence, the wheels would essentially be locked and not turning however.

Hope this helps.

PJ2
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Old 23rd Nov 2007, 00:47
  #233 (permalink)  
 
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Permit me a question - I hope it's not stupid:
The park brake applies pressure only to the main gear and not the center gear ...
Is this perchance to permit retraction of the center MLG while the aircraft is parked?
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Old 23rd Nov 2007, 01:08
  #234 (permalink)  
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barit1;

There is no mention of the reason for this design. I suspect given the sophistication of the aircraft, the answer is no, because there would be many ways to ensure the brakes on the center gear were not applied for retraction (gear swinging) on the ground. But I'm a pilot, not an AME so simply don't know.

PS - no question, earnestly asked, is ever stupid
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Old 23rd Nov 2007, 03:08
  #235 (permalink)  
 
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Engine run ups

It all seems to be asking a bit much from a parking brake to do a high power run up with a large 4 engine jet facing a jet blast wall. I say high power because that aircraft litterally climbed the wall.
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Old 23rd Nov 2007, 08:40
  #236 (permalink)  
 
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Originally Posted by Horas
It all seems to be asking a bit much from a parking brake to do a high power run up with a large 4 engine jet facing a jet blast wall. I say high power because that aircraft litterally climbed the wall.
Well, not quite. At 30 kts such a heavy beast has quite a lot of energy, and the wall is sloped. So until the tailskid would strike, the aircraft only had to "swing" around the main landing gear for the front section to "climb" the wall; not all that much energy involved, depending on the centre of gravity. Only after the tailstrike almost the entire airframe would have to be lifted.

The kinetic energy at 30 knots is enough to lift the centre of gravity by about 12 metres (this is true for any object in earth standard gravity). Well, without friction, but it seems quite possible that it would have climbed that wall the way it did, even with the engines completely shut down, once it had reached 30 knots and failed to stop normally.


Bernd
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Old 23rd Nov 2007, 08:44
  #237 (permalink)  
 
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The kinetic energy at 30 knots is enough to lift the centre of gravity by about 12 metres.
Please support statement with some math.....I know its basic physics but I want to see it done. This thread has become so boring I think a bit of formulae will spice it up
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Old 23rd Nov 2007, 09:30
  #238 (permalink)  
 
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Kinetic energy = 1/2 * mv^2
Potential energy = mgh

assume g=9.81, you can convert all the kinetic energy into potential energy when 1/2 * mv^2 = mgh

Mass cancels out, v^2 = 2gh

v = 30 knots = 15.4m/s, so v^2 = 237.16

so h = 237.16/(2 * 9.8) = 12.1metres.

This ignores friction and other losses.
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Old 23rd Nov 2007, 09:33
  #239 (permalink)  
 
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That`s cleared that up then
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Old 23rd Nov 2007, 09:40
  #240 (permalink)  
 
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missingblade, with pleasure

Converting Energy
(A tribute to Bob Hoover)

Kinetic energy is



where m is the objectís mass and v is its velocity. For simplicity SI or SI-
derived units (m, kg, s) are preferred.

Potential energy in earth gravity (assumed homogeneous for small heights)
is



where m is the objectís mass, h its altitude above an arbitrary reference,
and g is standard earth gravitational acceleration (9.81m/s/s).

To find out to which elevation a certain kinetic energy can propel an
object, we set the two energies equal, and do simple transformations:



So for v = 30knots ≈ 15.43m/s and g = 9.81m/s/s we get:



This is so basic, it's probably the entrance examination to be allowed to attend Physics 101
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