using full length of rwy for t/o
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I have a strong dislike for positions that are absolute, and this discussion is a good example. “I don’t make intersection takeoffs….”? Even if the airplane is light and the intersection gives 5,000’ of runway beyond your needs? Even if not taking the intersection means crossing an active runway twice, once while taxing and once more on the takeoff roll?
I will turn down an intersection departure if there is not a generous performance margin, including obstruction concerns. But otherwise, why not? A smooth flow of traffic is in and of itself in the interests of safety, a fact too many pilots (and all airline management) fail to consider.
And as already pointed out, the “altitude above you” can kill you if you go into the coffin corner trying to get there. And the “fuel in the fuel truck” may be the best place for it if it was beyond your needs and you now find yourself with one shutdown and mountainous terrain to climb through.
We get paid to think.
I will turn down an intersection departure if there is not a generous performance margin, including obstruction concerns. But otherwise, why not? A smooth flow of traffic is in and of itself in the interests of safety, a fact too many pilots (and all airline management) fail to consider.
And as already pointed out, the “altitude above you” can kill you if you go into the coffin corner trying to get there. And the “fuel in the fuel truck” may be the best place for it if it was beyond your needs and you now find yourself with one shutdown and mountainous terrain to climb through.
We get paid to think.
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Intersection takeoffs
How is it going to look at the inquiry? Captain so-and-so you elected to depart from intersection “whatever” leaving 2,000 feet behind you, given your less than 100% successful abort why did you do that? Personally I operate out of enough skinny and remote 6,000’ runways surrounded with rough terrain that I don’t like to pass up available pavement, that way I am “managing the risk” by managing my exposure. Something else to consider is how accurate are our weights-really? The various departments fulfill their functions and provide the input that eventually gets uploaded to the FMC to give us our performance. Are those weights 100% accurate 100% of the time-not a chance! Are we within 2% - I don’t really know. 5% - I sure hope so. At home we have a 12,000’ runway that ATC likes to depart from an intersection during daylight that provides 8,000’+. It’s subjective but if I have less than 100 passengers and am below 80% MGTW I will accept this intersection, otherwise I’ll ask the FO to “tell him I want full length”.
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"I'll only accept full length departures."
What poppycock.
Rwy 31L KK at JFK is 10,700' long. Full length is 14,572' feet long.
Departure choices are 22L or 31L KK. Rwy 22L is 11,351' with a 45-60 minute taxi out. Oops, you're heading SW or W, and that departure runway is 31KK.
So, do you stand on principles and demand Rwy 31L full length?
Please post on Pprune when you'll going to demand Rwy 31L full length when even 767-300's are accepting 31L KK. I'd love to hear the conversation with JFK ground, especially with the short tempered controller.
What poppycock.
Rwy 31L KK at JFK is 10,700' long. Full length is 14,572' feet long.
Departure choices are 22L or 31L KK. Rwy 22L is 11,351' with a 45-60 minute taxi out. Oops, you're heading SW or W, and that departure runway is 31KK.
So, do you stand on principles and demand Rwy 31L full length?
Please post on Pprune when you'll going to demand Rwy 31L full length when even 767-300's are accepting 31L KK. I'd love to hear the conversation with JFK ground, especially with the short tempered controller.
Pontious:-
2 Brilliant posts IMHO and PJ sounds like his 'masters' are so rich they don't have a care regarding fuel - unless he owns the PJ himself! I can put on 'pretty much what I like' regarding fuel but I have to justify it. That sounds reasonable to me. All this rubbish about 'automatons' is just cliche as is the old worn out 'Sky above you' nonsense. Don't be concilliatory, PJ doesn't care what we think. Let him fly his shiny jet at 45,000 ft or even higher if he can. Keeps him out of our way.Then he can get back to the flying club and impress people.
2 Brilliant posts IMHO and PJ sounds like his 'masters' are so rich they don't have a care regarding fuel - unless he owns the PJ himself! I can put on 'pretty much what I like' regarding fuel but I have to justify it. That sounds reasonable to me. All this rubbish about 'automatons' is just cliche as is the old worn out 'Sky above you' nonsense. Don't be concilliatory, PJ doesn't care what we think. Let him fly his shiny jet at 45,000 ft or even higher if he can. Keeps him out of our way.Then he can get back to the flying club and impress people.
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Fullwings
Just in case others are as dim as me, can you elaborate? It seems to me that when you take the full length available, rather than taking an intersection, you are increasing the TODA while the ASDR remains constant (expect perhaps for minor net slope variations).
Conversely, when you take an intersection you reduce the TODA, with a constant ASDR.
The ASDR, being a function of the aircraft condition and weight, together with ambient met and other parameters, won't change, will it, unless you use different power settings to reduce it to match the TODA? Is that the basis of your argument?
If you are saying that you you simply use a higher power setting for the intersection departure, so it's just as safe as taking full length at lower power settings, I'm not sure I really buy that. Most of the unknown variables are still present in the calculation.
It seems also to have a flaw in so far as it raises the question; "why not maximise safety and use the same - higher - power setting you would have used from the intersection, but taking the full length?".
I'm fumbling here, as you can probably tell. Can you elucidate a bit?
if you use assumed temperature derates on your average <3,000m (10,000') runway, you will frequently end up with a balanced field, i.e. ASDR = TODA so a V1 reject will use it all, no matter where you start from.
Conversely, when you take an intersection you reduce the TODA, with a constant ASDR.
The ASDR, being a function of the aircraft condition and weight, together with ambient met and other parameters, won't change, will it, unless you use different power settings to reduce it to match the TODA? Is that the basis of your argument?
If you are saying that you you simply use a higher power setting for the intersection departure, so it's just as safe as taking full length at lower power settings, I'm not sure I really buy that. Most of the unknown variables are still present in the calculation.
It seems also to have a flaw in so far as it raises the question; "why not maximise safety and use the same - higher - power setting you would have used from the intersection, but taking the full length?".
I'm fumbling here, as you can probably tell. Can you elucidate a bit?
Capot
I'm sure you know all this - I'm expanding for those who may not have come across all these concepts:
Most modern airline SOPs are set up for the use of derates, usually the fine-grained control you get using assumed temperature. This is for engine life, maintenance issues, costs, noise, etc. I don't think they are mandatory anywhere - you can always use more thrust if you like - but I would hazard that the majority of pilots flying commercial jets today 'buy in' to the concept.
When you are preparing to take off from any runway you get the 'figures' (I hope
), either manually or through some sort of computerised performance calculation. Depending on who you work for, 'intersection data' may be available electronically or published in a manual.
What has been worked out for you, when you obtain a derate for a particular takeoff position, is the lowest thrust setting that satisfies many criteria, including obstacle clearance, EO climb limits, WAT limits, Vmcg & Vmca problems, close-in turns, etc. As you increase the amount of runway available, the required thrust will reduce until you are limited by one or more of the above. On a 'normal' sized runway, if there are not too many significant obstacles or other extreme environmental conditions, the outcome of the calculation will often be to make ASDR = TODA, as that becomes the limiting factor.
*** My point is that if you are using full length and the derate from the last paragraph, you are not in any significant way increasing the margin for a V1 reject over someone who did the same calculations using an intersection and came up with less of a derate. ***
An interesting effect of this is that you only start to see a difference when using long runways or light weights: going for 2,500m over 2,200m will probably not affect the V1 case but taking 4,000m over 3,000m most likely will. Somewhat counter-intuitive as many think it's the other way round.
Why not *really* maximise safety and always use full power? What's so special about the thrust needed from a random intersection? It's a bit like adding more fuel "for Mum": where do you stop? I think this is a key issue - either you have confidence in the aircraft performance or not; if it doesn't do what the book says, there should be an ADD with a performance decrement to apply or it should go back in the hangar to be fixed.
From a practical point-of-view, if I think there's a possibility of an intersection departure, then I'll set up for that then keep that configuration if I get sent for a longer intersection or the full length. This is more from a distraction management perspective than trying to increase margins. If you are derated, then you'll get a margin from the positive effects of real air density vs. assumed, anyway.
Yes, they are but that's something we have to live with every day we go to work. If you think the aircraft is heavier than it should be, get it weighed or use more thrust, wherever you're taking off from...
(I'm hoping that JT, mutt or one of the other performance experts will step in and help out here, or at least correct my mistakes! C'mon guys, where are you?!?)
I'm sure you know all this - I'm expanding for those who may not have come across all these concepts:
Most modern airline SOPs are set up for the use of derates, usually the fine-grained control you get using assumed temperature. This is for engine life, maintenance issues, costs, noise, etc. I don't think they are mandatory anywhere - you can always use more thrust if you like - but I would hazard that the majority of pilots flying commercial jets today 'buy in' to the concept.
When you are preparing to take off from any runway you get the 'figures' (I hope
), either manually or through some sort of computerised performance calculation. Depending on who you work for, 'intersection data' may be available electronically or published in a manual.What has been worked out for you, when you obtain a derate for a particular takeoff position, is the lowest thrust setting that satisfies many criteria, including obstacle clearance, EO climb limits, WAT limits, Vmcg & Vmca problems, close-in turns, etc. As you increase the amount of runway available, the required thrust will reduce until you are limited by one or more of the above. On a 'normal' sized runway, if there are not too many significant obstacles or other extreme environmental conditions, the outcome of the calculation will often be to make ASDR = TODA, as that becomes the limiting factor.
*** My point is that if you are using full length and the derate from the last paragraph, you are not in any significant way increasing the margin for a V1 reject over someone who did the same calculations using an intersection and came up with less of a derate. ***
An interesting effect of this is that you only start to see a difference when using long runways or light weights: going for 2,500m over 2,200m will probably not affect the V1 case but taking 4,000m over 3,000m most likely will. Somewhat counter-intuitive as many think it's the other way round.
"why not maximise safety and use the same - higher - power setting you would have used from the intersection, but taking the full length?"
From a practical point-of-view, if I think there's a possibility of an intersection departure, then I'll set up for that then keep that configuration if I get sent for a longer intersection or the full length. This is more from a distraction management perspective than trying to increase margins. If you are derated, then you'll get a margin from the positive effects of real air density vs. assumed, anyway.
I'm not sure I really buy that. Most of the unknown variables are still present in the calculation.
(I'm hoping that JT, mutt or one of the other performance experts will step in and help out here, or at least correct my mistakes! C'mon guys, where are you?!?)
