To all you armchair quarterbacks, something to think about.....

Was the aeroplane AT the limit weight? if not there is some margin built in...typically the aeroplanes depart a couple of tonnes below the calculated limit weight because of the allowances made at the planning stage....

Secondly, in terms of obstacle clearance, there are no significant obstacles off Runway 23 at Adelaide....

Thirdly, where do you draw the line... If you were taking off from edwards Air force base with a 10 mile long runway would you always go full length in case you reject? NO? Well where do you draw the line. The people on the day made a decision based on a number of factors, the primary one being what the analysis manual said... from memory the D intersection gives you about 2300 m (I stand to be corrected though), does that mean that you would never take off from Cooly at 2000 odd metres? Or runway 27 in Melbourne - I assume that you always take full length 34 or 16 because you MIGHT need it, even though the analysis manual says 27 is OK for your operation.

Flying aeroplanes is an exercise in risk management, we as pilots make considered decisions everyday, and we make those decisions based (mostly) on sound advice from manuals, training etc.

PS grange Guzzler, people in glass houses spring to mind - without knowledge of what was going on you are making an uninformed criticism of the crew.

You are not an aviation consultant and or television commentator by any chance are you?

Without getting into the nitty gritty of it all there is one point Ii'd like to make.

DHD, you're absolutely correct about the 'risk' management- although I prefer to call it 'threat and error' management- with a side order of 'benefit' thrown in! ;) I guess the difference is that by going to the full length decreased the 'threat (which I acknowledge was relatively minor) with no loss of commercial benefit. All of aviation has to be weighed up in 'threat' and 'benefit'. What is the threat of the intersection take off? Is it worth the benefit (and there often IS a benefit) is the next question that has to be asked.

What is the threat of intersecction, greater than full length. What was the benefit? Increased taxi way utilisation for company aircraft? Decreased taxi time and therefore greate schedule reliability? From what I can see in GGs example, there was nil benefit. Therefore, why not lower the threat a bit from 'low' to 'virtually nil'.

Cunning,

You are a twit. Oz bashing – I am an ozzie. Whats your point.
Yes, the example was ADL – I haven’t flown in oz for 2 years and have forgotten the numbers – runway lengths etc.

Is terrain clearance less from adl 23 intersection. Cant remember but if it is – so what.

CASA allow it. AN,VB,QF all allow it. The ops engineers spend a lot of time and money drawing up intersection charts to enable it. I have seen all airlines do intersection departures from DRW,SYD,MEL,ADL,BNE,CNS and others I guess. Is terrain clearance compromised. I guess so.

If you define professionalism as always doing full-length departure in a lightly loaded short flight twin jet then good for you. Most others apparently don’t.

do any operators change their V1 with de-rate? I would be most suprised.

I spend a week each year at Boeing. I see the performance courses at both grades and know many graduates of them. Without exception skilled and dedicated people but they believe in the numbers and would offer up their first born such is their faith.

However, they are not at the pointy end.

I'm glad Dehavillanddriver offered up the example of Edwards and, as you're all using the internet, I'd like you to take a look at another runway - Moses Lake. It's significant because, as yet, Airbus don't have much penetration into the Oz market.

Use the free satelite imagery viewing sites to look at the runway - all 15,000 feet of it. That's where your performance figures were derived. Note the witness marks for the tests and the parallel nature of them as the TP's sidestep to get clear pavement - it is a competiitve business and they want the best figures possible.

Once you've viewed the images here's the sum up:

They are not performing RTO's on the caked contaminated crap we face but the figures are based on those conditions you see there. We do not have the luxury of sidestepping the touchdown zone on our real life runways.

For many intersection take offs it doesn't matter if you are tonnes underweight - the touchdown zone is where we are all applying maximum braking, the tyres (remember them?) are now very hot and we are digging them into the contamination while still a more than a thousand feet from the stop lights and the antiskid has ensured we're now carrying an even coating of crap with us.

Nobody is denying these takes off's have their place in operations but a wide eyed acceptance of performance data is very dangerous. The figures are as much the domain of the marketeers as the flight test department. There is no other reason for them to spend the last generation fighting all efforts to make them reflect the real lives of folks on the line.

Finally, for those of you into the extreme sport of competitive derating - have you ever researched - or your company passed on - the reductions in N1 or EPR that actually extend engine hot end life versus the thrust settings that are mere willy waving? Some interesting work on the subject that never reaches those on the line. Again, you're viewing this on the internet and you can google your way into knowledge if you care rather than just here to enjoy taking a poke at each other.

Here's the real performance calculation:

Intersection + willy waving derate + contaminated upwind touchdown zone + long taxi with multiple turns = baffled performance engineeer telling us it was the pilots' fault coz the figures said you could stop.

Regards to all,
Rob

Sorry Cactus, but your appreciation of TODR vs ASDA is scant to say the least. Firstly you are using apples vs oranges. Even if you said TODA vs ASDA, your so called 'balanced field' definition is wrong.
Lets pretend, for a moment, that you meant ASDR = TODR, I may buy into that...briefly, but thats only a definition of a Balanced Field, and operationally not all that common or desired. For instance, if you had a runway with obstacles in the 2nd, 3rd or final, and a subsequently reduced TOW for the grad., then why the hell would you want a balanced field? A long rwy like Sydney 16R for instance will bring you into a Brake Energy limit before you get to your other limits, and MTOW becomes the operational limit. Again your Balanced Field theory is devoid of reason. If you want to screw with your V1 / VR ratio to achieve this, other factors will prevent you from doing so. May I quote my boeing AFM.......
"The takeoff distances for this airplane are unbalanced because the V1 for a balanced field would normally exceed VR with anti-skid operating"
Now, 'wet' rwys can be a little more tricky, but watch your definition of 'wet' on groved rwys.
Further, and all Required / Available lengths aside, to judge the reasoning for departures from other than full length you must know all the factors effecting the performance of the airplane at the time.
What was its Actual TOW?
.....its limiting TOW - and its always nice to know if its RWY, brake temp or Obs related.
....and the margin.
So, and I hope I haven't bored you too much, the answer to why DJ did what they did is quite as simple as the ol' "Why does a dog lick its nuts?"
cheers
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