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747 Crash At Brussels

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747 Crash At Brussels

Old 26th May 2008, 14:17
  #81 (permalink)  
 
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Just a couple of thoughts/questions for you guys.

76 tonnes sounds a fairly big payload for a -200F on a 6-hour flight. Rwy 20 is about 650m shorter than 25R, and significantly uphill; wind was light and variable (#51). opale4 tells us (#54) that 20 is the preferential runway on Sundays, but 25R would presumably have been granted if performance considerations could be cited. The two runways have closely adjacent thresholds, but one assumes (and very much hopes) that the crew knew they were taking off on 20.

Interesting that it looks almost as if the back of the fuselage has tried to overtake the front. Is this a common feature of serious overrun accidents?

Can anyone tell us how many hundreds of metres the aircraft over-ran? Banks/roads/railways predominate overruns worldwide. This is because, since the advent of the B707, the runways of old airfields have been extended and extended into surrounding areas, most of which are (or have become) suburban. Rarely is an all-new airfield built, like Munich 2.

hyperactive,
You seem to know about aircraft structures, but part of your post is a bit cryptic (#100):
no spoilers no thrust reversers gear apears stowed or at least partialy”
Are you saying that the reversers may not have been fully stowed, or are you referring to the landing gear in that sentence? There are several possible reasons for the spoilers not being extended in the photos, including instinctive retraction by the pilot as the aeroplane stopped. Conversely, pilot reselection of forward idle − and giving time enough for them to stow before the engines shut down − is unlikely, particularly in this instance.
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Old 26th May 2008, 14:45
  #82 (permalink)  
Hardly Never Not Unwilling
 
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The one that appears curled might be one of the fuselage spars or "ribs". Just a guess.

tgdxb asked:

Out of curiosity, given the airlines' known care for security/safety, could flying crews help me understanding on what basis--weather conditions permitting--, they would accept taking off from 02/20 while knowing that 25R gives them more rwy length? I have to admit that this is a mystery to me.
It's routine to use a runway other than the longest for a number of reasons. ATC determines the runway in use and assigns it to the flight, usually before taxi. Wind direction, noise abatement, runway maintenance, traffic flow - all these and more affect the runway assigned.

The crew and/or company take the assignment, run the numbers, and if the takeoff can be made within aircraft parameters, accept it. If they can't accept it, they find an alternative or don't go. To take off on RW 02 with numbers run for 25R at EBBR would be a gross pilot error, and is not likely to have happened here.

Sometimes intersectional takeoffs are assigned leaving hundreds of feet of perfectly useable concrete behind, Ohare 32L at the T10 intersection and Anchorage 32 North of 07L come to mind. If you can't take off at the intersection you ask for full length, even though it might gum up the works.

At busy airports, time on the runway is the precious commodity. ATC wants max flow to get the most operations per hour. They have to satisfy the noise hawks as well. Compromises are made, but we trust never outside demonstrated safety parameters.

Other compromises that bother me a bit are flying big jets into short fields like Chicago Midway and Orange County John Wayne. Everything has to go pretty much right or the eyes can definitely be opened and watered. These airports are used to make a buck.

Don't mention the parking garage at San Diego.
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Old 26th May 2008, 16:48
  #83 (permalink)  
 
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BENTHERE WROTE:

The crew and/or company take the assignment, run the numbers, and if the takeoff can be made within aircraft parameters, accept it. If they can't accept it, they find an alternative or don't go. To take off on RW 02 with numbers run for 25R at EBBR would be a gross pilot error, and is not likely to have happened here.
Finally, someone with some sense.

I'm not saying it's impossible that the crew mis-read the numbers or forget something, but to say thats a good theory as to why this accident happened is ridiculous. This is basic aviating.

I would be VERY VERY surprised if they didn't have the runway analysis for rwy 20 as well as the other runways. The airline I work for we have the runway anaysis for EVERY runway prior to departure so that if there is a last minute rwy change, it's an easy check to make sure we can take off at that weight.
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Old 26th May 2008, 17:24
  #84 (permalink)  
 
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"76 tonnes sounds a fairly big payload for a -200F on a 6-hour flight"

??
Just t'other day I took 96 tonnes and 80 tonnes of fuel on a 200F 6 hours 10 mins so no, 76T is not a lot...........
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Old 26th May 2008, 17:41
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Chris (Scott), judging from the photos and Google Maps, I'd guess the overrun was around 1,000 ft (300m). The nose was extended (not much) over the slope of the railway trench, sooo the sums are averaged...

:-)

S.
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Old 26th May 2008, 18:01
  #86 (permalink)  
 
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Still, wouldn't you prefer a longer rwy which would improve your safety envelope?
Obviously, I understand that you have to work within external constraints, such as those from ATC, regulations etc.
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Old 26th May 2008, 18:21
  #87 (permalink)  
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tgdxb

Though not a consideration pre T/O, had the A/C overrun on concrete or Asphalt, the likelihood of Fuel ignition is far higher than not. There was no fire post landing re: BA038, (though of course far less fuel left to burn). Since we're all talking post incident, it is fortunate the A/C launched on the "shorter" runway. (IMO).

Airfoil
 
Old 26th May 2008, 23:53
  #88 (permalink)  
 
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Performance

Thanks superspotter,

I did say “fairly big”. Engines look like JT9Ds; are yours CF6s? is there much difference in thrust? Anyway, don’t suppose you’ve got any figures for EBBR Rwy 20? Failing that, using conservative figures: balanced field of 2987m (9800ft); 0.7%UP; 120ft amsl; T/W 2kts; +20C.

If you agree on a ball-park figure of 6 hrs to OBBI, how about FOB 75T for the 76T payload?

How much fat might that leave us with?

Thanks for the overrun info, VAFFPAX.

Earl, you are reminding me of the bad old days in the Seven-oh. Often, we’d never have stopped from V1. But are you sure you’d get airborne, on the remaining pavement, after an engine failure at 85kts? [Assuming you could use nosewheel steering to keep it straight below Vmcg.] There are tyre failures and tire failures, of course. We need a performance monitor (as we were saying 20 or 30 years ago…).
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Old 27th May 2008, 07:48
  #89 (permalink)  
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They were very lucky it came to a sudden stop. From a close look at the wreckage the aircraft was up on its gears right across the overrun, but as it passed through the airport fence the gears sank in, folded backwards and the aircraft fell on its belly, breaking into three pieces as it dug in. If it had carried on it would have gone down the slope and nosed into the railway.
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Old 27th May 2008, 08:53
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the gears sank in, folded backwards and the aircraft fell on its belly, breaking into three pieces as it dug in.
Hmm. I'd put money on the aircraft 'cracking up' before the RTO. The bangs heard by the crew could well have been some pretty significant structures letting loose. I can't see a structurally sound airframe breaking up, as this did, from the roughest of (fairly) low speed over-runs.
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Old 27th May 2008, 11:24
  #91 (permalink)  

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Just to correct the figures, TOW 305200kg, gross load 74200kg (USPS Mail) & fuel 81600kg. Dredging the memory for -200 dispatch, rwy 20 should be within limits.

RT
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Old 27th May 2008, 11:43
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Another possibility is that the forward break occurred when the nose (with or without gear down) went over the edge of the railway embankment.
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Old 27th May 2008, 11:52
  #93 (permalink)  
 
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RampTramp,
I guess the argument is less about whether within feasibility limits than what happens in case something unexpected occurs, and whether rwy 20 was a wise choice... which IMHO I think not be a wise choice.
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Old 27th May 2008, 12:19
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tgdxb,

The take-off analysis gives you a maximum weight for the runwaylength, runwaycondition, temperature and pressure altitude (with possible weightpenalties for deferred items). A balanced field take-off is where the accelerate-stop distance is the same as continuing the take-off at v1 with an engine failure and cross the runway end at 35ft.

The weight for that runway(02) can be around 340T (CF6 engines). I don't know for JT9's but probably no big difference.

If their TOW was equal or lower than the max weight for that runway under that conditions, there is no problem (theoretically) to make it till v1, and stop within the runway-length.

Blowing a tyre gives you reduced braking-capability and is normaly no reason for an abort at high speeds (above 100kts)

So it was wise! As it is for smaller planes to use intersection take-offs iso the full runwaylength.

But let's wait and see what the reason was for the abort!
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Old 27th May 2008, 12:28
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Just for info after leaving RWY20 the 747 went over the ringweg (road around airport). This road is situated about 3 to 4 meters below the THR of RWY 02. So probably the structural damage happened when the aircraft drifted over the "ditch" of this road. nose went slightly down towards the road, NWG broke off, pushing the nose more down, enormous pressure on the top skin of the fuselage, causing it to break. Main landing gear collapses and the tail is still above the embankment, causing it to break. on jetphotos.net you can see the aircraft from the left hand side and you'll see the tail is still on the embankment.

Greetings
BM
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Old 27th May 2008, 12:30
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Just another thing.
The aircraft took off (or tried to) from RWY 20!
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Old 27th May 2008, 12:48
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....... NWG broke off, pushing the nose more down, enormous pressure on the top skin of the fuselage, causing it to break.
Ah, so it's the NWG that keeps the forward section from snapping off. That would make jacking-up an event to watch.
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Old 27th May 2008, 13:02
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QUOTE : Ah, so it's the NWG that keeps the forward section from snapping off. That would make jacking-up an event to watch





Yeah, well jacking up at 100 kts with 76 tons of CARGO and another 70's or so ton fuel (read INERTIA) would lead probably to the same structural damage.


Always welcome...
BM
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Old 27th May 2008, 13:31
  #99 (permalink)  
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So I would guess, the break up happened after the overrun.
Yes. The tyre tracks gradually run off the centre of the runway to the right and then pass across the grass to the localiser. Where the aircraft passed through that, the tracks end as the gears collapsed. The subsequent aircraft fuselage track indicates a stop in very short order. Thus, it appears that the aircraft broke apart as it came to a stop with the gears collapsed, as the rear end tried to overtake the nose, which was digging in hard at that point.

Last edited by Blacksheep; 27th May 2008 at 13:58.
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Old 27th May 2008, 14:17
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R/W 20 would not have been too short for this take-off. The same result given the same circumstances would have happened if R/W 25 had been used. This is because take-off calculations give the crew the lowest power setting that will achieve V1 at the point where there is just enough runway ahead to stop again. So the difference on r/w 20 compared to 25 is that on 20 the power setting would have been more, but the stopping distance on either runway would have been the same.

High speed abort never a nice situation having had one myself in a 747-200.

My guess is a weight shift after V1 (perhaps on rotation), thus making the a/c unflyable (so taking away the choice of trying to still get airbourne), but sadly not enough runway length ahead to still stop.

CL

Looks to me like crew did a fine job
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