using full length of rwy for t/o
Joined: Dec 2003
Posts: 2,349
Likes: 845
From: Tring, UK
Maybe the advocates of full length take so much extra fuel that they are too heavy for an intersection departure? 
I think the fundamental issue here is understanding aircraft performance. The more you know about this subject, the easier it becomes to make rational decisions without relying on instinct or flying 'lore'. There is so much useful information out there and, even better, knowledgeable professionals who can explain it to those who are interested. There are several who frequent this forum, for instance.
Personally, I don't get too worried about taking off vs. runway length. If the calculations say yes and the input and output data passes a sanity check, then I go. You are departing from a known position and can assess actual conditions before making for the skies. I get more concerned when it comes to landing, especially on more limiting runways as there are too many variables: the exact TD point is unknown, as is the speed; how wet or contaminated is it? What's the braking action? Wind component? Small changes in any of these can have a large impact on the achieved landing run and a combination of subtle movements the wrong way in several parameters can increase your LDR enormously, possibly beyond the end of the runway...
As I said before, I don't think anyone should be criticised for taking full length over a possible intersection departure - it's what you're happy with. If it's costing fuel and time, however, it might be a worthwhile exercise to consider whether what you're doing is based on reason or the piloting equivalent of childhood fears. Just a thought...
I think the fundamental issue here is understanding aircraft performance. The more you know about this subject, the easier it becomes to make rational decisions without relying on instinct or flying 'lore'. There is so much useful information out there and, even better, knowledgeable professionals who can explain it to those who are interested. There are several who frequent this forum, for instance.
Personally, I don't get too worried about taking off vs. runway length. If the calculations say yes and the input and output data passes a sanity check, then I go. You are departing from a known position and can assess actual conditions before making for the skies. I get more concerned when it comes to landing, especially on more limiting runways as there are too many variables: the exact TD point is unknown, as is the speed; how wet or contaminated is it? What's the braking action? Wind component? Small changes in any of these can have a large impact on the achieved landing run and a combination of subtle movements the wrong way in several parameters can increase your LDR enormously, possibly beyond the end of the runway...
As I said before, I don't think anyone should be criticised for taking full length over a possible intersection departure - it's what you're happy with. If it's costing fuel and time, however, it might be a worthwhile exercise to consider whether what you're doing is based on reason or the piloting equivalent of childhood fears. Just a thought...
Last edited by FullWings; 16th November 2008 at 08:39. Reason: and grammer speling
Joined: Jun 2005
Posts: 1,420
Likes: 1
From: AEP
Those of you who criticize the idiots (like myself) who always use maximum runway length should think of the many who attempted to reject a takeoff (at speed below V1 like the book says) and... were not able to stop before the end of the said runway.
xxx
With my respect to the superior pilots, and other geeks and nerds.
Happy contrails
xxx
With my respect to the superior pilots, and other geeks and nerds.
Happy contrails
Joined: Dec 2003
Posts: 2,349
Likes: 845
From: Tring, UK
...think of the many who attempted to reject a takeoff (at speed below V1 like the book says) and... were not able to stop before the end of the said runway.
Do you have links/citations for any of the "many" above? I only ask as I've spent some time trawling the 'net for reports of overruns and all I can find are references to landing accidents & post-V1 rejects. It would be interesting to view an objective publication on a sub-V1 incident to see where it went wrong...
Joined: Jan 2004
Posts: 794
Likes: 21
From: England
At busy airports with the complexities of SID's, noise departure routes, vortex spacing, flow control etc intersection departures are a very useful tool for ATC to achieve the desired take-off sequence and therefore keep ground delays to a minimum.
Joined: Jun 2005
Posts: 390
Likes: 0
From: London
Do you have links/citations for any of the "many" above?
If the balanced field calculations we use every day make us take an unacceptable risk, statistics would show it. So until such a study comes out, I have no reason to refuse an intersection departure on safety grounds.
Cheers,
P
Joined: May 2002
Posts: 942
Likes: 0
From: dubai
There is an added problem with intersection departures.
A lot of airports that I use, the runway available from a nominated intersection to the end of that runway, in distance, is not readily available. All airports should have this information displayed either on the airport chart or at the intersection holding point in question. Yes I have a ruler but am not into guess work.
However ICAO cannot even agree to implement an agreed ICAO language, so living in the hope of anything else conducive to safety happening, is wishful thinking.
A lot of airports that I use, the runway available from a nominated intersection to the end of that runway, in distance, is not readily available. All airports should have this information displayed either on the airport chart or at the intersection holding point in question. Yes I have a ruler but am not into guess work.
However ICAO cannot even agree to implement an agreed ICAO language, so living in the hope of anything else conducive to safety happening, is wishful thinking.
Joined: Jun 2005
Posts: 1,420
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From: AEP
I fail to be able to compare the psychology of some pilots here, who object to my preference in having the longest runway possible, for a possible rejected takeoff situation potential. Is this new generation of pilots not trying to "bank" additional safety in their way to operate airplanes...?
xxx
All of us have one thing in common. We all operate our airplanes from A to B by trying to gain "extra" safety (or economy) here and there. This is in the same order than, as an example (for a 747) adding an extra 1000-2000 kilos of fuel, or computing a certain takeoff for an extra (higher) 5º temperature because it is likely that the current ATIS temperature will rise another (say) 2 or 3º by the time you line-up for departure.
xxx
For me, the gentlemen here above that prefer an intersection to a full length runway will then never take that extra 1000 kilos of fuel, or will be satisfied with the cooler ATIS temperature recorded 45 minutes ago. For me, an extra 1,000 feet of runway might save an airplane. I operated 747s (and 707/DC8s) long enough in my career, at a weight close to (if not equal to) the runway limit weight, and taking off with a liftoff in the last 1000 feet of that runway.
xxx
Here in Pprune, we constantly read future pilots who question speed V1 and rejected takeoffs. Many qualified pilots all agree of a "decision V1" that should be done some (say) 5 knots (or more) below V1. I use the same philosophy, if not in terms of speed, then in term of runway available in front of the airplane. The more runway, the better. Sorry...
xxx
You question rejected takeoff accidents...? The one that comes to my mind is the Kalitta 747 BRU accident at the end of runway 20 (last May). I am certain the crew regretted not to have used 25R, which is longer.
xxx
I can recall a personal incident in DXB, 25 years ago, where I took off with a DC8-63F which got overloaded (by some 10 or 15 tonnes of freight) because of a confusion between kilos and pounds. If that day, I would have used a shorter runway (i.e. intersection), I might not be here today to write about it.
xxx
This is my last week as an active pilot, as I retire friday. I might continue to contribute to this forum in trying to promote safety with my good words of wisdom as an "old fart" as a "hasbeen" to coin a word opposite to "wannabee".
xxx
Appears that my career reputation was good, having been invited to continue as pilot training consultant, from a desk, in a classroom or "stimulators"... So, if not too busy in checking bikinis at the beach, emptying a few beers or wine, I might visit Pprune at times to "rant" about long runways and intersection takeoffs. Free for you, my detractors, to criticize my recommendations.
xxx
Happy contrails, always.
xxx
All of us have one thing in common. We all operate our airplanes from A to B by trying to gain "extra" safety (or economy) here and there. This is in the same order than, as an example (for a 747) adding an extra 1000-2000 kilos of fuel, or computing a certain takeoff for an extra (higher) 5º temperature because it is likely that the current ATIS temperature will rise another (say) 2 or 3º by the time you line-up for departure.
xxx
For me, the gentlemen here above that prefer an intersection to a full length runway will then never take that extra 1000 kilos of fuel, or will be satisfied with the cooler ATIS temperature recorded 45 minutes ago. For me, an extra 1,000 feet of runway might save an airplane. I operated 747s (and 707/DC8s) long enough in my career, at a weight close to (if not equal to) the runway limit weight, and taking off with a liftoff in the last 1000 feet of that runway.
xxx
Here in Pprune, we constantly read future pilots who question speed V1 and rejected takeoffs. Many qualified pilots all agree of a "decision V1" that should be done some (say) 5 knots (or more) below V1. I use the same philosophy, if not in terms of speed, then in term of runway available in front of the airplane. The more runway, the better. Sorry...
xxx
You question rejected takeoff accidents...? The one that comes to my mind is the Kalitta 747 BRU accident at the end of runway 20 (last May). I am certain the crew regretted not to have used 25R, which is longer.
xxx
I can recall a personal incident in DXB, 25 years ago, where I took off with a DC8-63F which got overloaded (by some 10 or 15 tonnes of freight) because of a confusion between kilos and pounds. If that day, I would have used a shorter runway (i.e. intersection), I might not be here today to write about it.
xxx
This is my last week as an active pilot, as I retire friday. I might continue to contribute to this forum in trying to promote safety with my good words of wisdom as an "old fart" as a "hasbeen" to coin a word opposite to "wannabee".
xxx
Appears that my career reputation was good, having been invited to continue as pilot training consultant, from a desk, in a classroom or "stimulators"... So, if not too busy in checking bikinis at the beach, emptying a few beers or wine, I might visit Pprune at times to "rant" about long runways and intersection takeoffs. Free for you, my detractors, to criticize my recommendations.
xxx
Happy contrails, always.
Joined: Nov 2005
Posts: 937
Likes: 0
From: Isle Du Cyber
Full Use
A pilot I worked with many years ago was an ex Navy carrier pilot.
On carriers you use the full length.
When he started flying commercially he told be the runway behind on take-off is no good when things go wrong so always use the full length.
From what i understand the CAA made a recommendation a couple years ago about light aircraft with retractable undercarriages not to raise the gear to early on departure as on some runways you could land back on if there was a problem on take off.
On carriers you use the full length.
When he started flying commercially he told be the runway behind on take-off is no good when things go wrong so always use the full length.
From what i understand the CAA made a recommendation a couple years ago about light aircraft with retractable undercarriages not to raise the gear to early on departure as on some runways you could land back on if there was a problem on take off.
Joined: May 2002
Posts: 942
Likes: 0
From: dubai
BelArgUSA
Good luck on your "last" commercial flight on Friday. don't get too wee weed!! We don't want to read in some Spanish rag of a "non drinker gone ape s**t and smashing the town up".
Please continue to contribute to this forum as I for one will read and value your input.
Will probably upset the "young" guys and gals, this, but there is clearly no substitute for experience.
Good luck on your "last" commercial flight on Friday. don't get too wee weed!! We don't want to read in some Spanish rag of a "non drinker gone ape s**t and smashing the town up".
Please continue to contribute to this forum as I for one will read and value your input.
Will probably upset the "young" guys and gals, this, but there is clearly no substitute for experience.
Last edited by doubleu-anker; 17th November 2008 at 09:58.
Joined: Jun 2005
Posts: 390
Likes: 0
From: London
BelArgUSA,
I don't think many of us would deny the additional "just in case" advantage of having a longer piece of tarmac in front rather than behind. So if no advantage is to be gained by picking the shorter one, I also pick the longer version. But if the shorter one will get me airborne on time, either because I sneak in before the next arrival or because I get ahead of someone who has no slot, I don't think it's poor airmanship to pick the short version. To refuse any intersection departure on principles seems over the top. To me, it would be like refusing to use assumed temperature thrust settings - just in case.
Enjoy your last flight! Wine and bikini checking sounds like a good plan
P
I don't think many of us would deny the additional "just in case" advantage of having a longer piece of tarmac in front rather than behind. So if no advantage is to be gained by picking the shorter one, I also pick the longer version. But if the shorter one will get me airborne on time, either because I sneak in before the next arrival or because I get ahead of someone who has no slot, I don't think it's poor airmanship to pick the short version. To refuse any intersection departure on principles seems over the top. To me, it would be like refusing to use assumed temperature thrust settings - just in case.
Enjoy your last flight! Wine and bikini checking sounds like a good plan
P
Joined: May 2007
Posts: 1,415
Likes: 2
From: Europe
and the safety of my flight is guaranteed by my performance calculations.
And one of those "calculations" is the one that says that you, not them, will be able to bring your aircraft to a safe stop from V1, regardless of how degraded the actual conditions for that stop are compared with the demonstration at the factory.
Are you sure your brakes and tyres are perfect? Are you sure that the stopway and RESA you're heading for are perfect? Yes? Why, exactly? Check them out, did you? It's only a given at major airports; many smaller ones are rather deficient in this area.
Have you looked at the runway surface? Measured its friction? No? Of course not it's done for you. But when? and how carefully? And did a bean-counter decide it was good enough when it isn't? No, of course not, it's "guaranteed".
It won't be your fault, of course, if the stop from V1 doesn't go quite according to plan. Someone else's calculations or actions will have let you down.
So that's all right then; carry on using the intersection because performance is "guaranteed".
Joined: Sep 2008
Aviation Qualifications: ATPL
Posts: 3,435
Likes: 1,202
From: 41S174E
NZAA has implemented a reccommendation, by some body or other, not to allow intersection departures . As I understand it, this is to do with minimising the risk of runway incursions, or whatever, not to do with perf issues.
Joined: Dec 2006
Posts: 2,486
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From: The No Transgression Zone
BelArgUSA ---First may I wish you a very happy last flight --- I know you'll grease it ---
But regarding the V-5 that would be ok if you're and you know for sure that you ASD limited ---but if you're obstacle limited one may well sink below /at--the NTOFP [especially hot and high where that is more usual]--or-wind up with zero screen height when all of the perf assumptions are hidden from the view of pilots ----I think that one should simply use V1---today's operation 2 crew FMC run FD's are not good places to do such a thing --they gave your generation the performance data in the AFM set to think through such a decision---I don't think a today's operational philosophies permit such a thing to be done safely --believe me --- I do see where you are coming from but without that information it's a crap shoot
One could always use less derate or a lower than max [limiting] AT to increase performance margins although quite frankly I don't think airlines give enough training or data to safely artificially lower V1 as they may end up flying into the side of some ridge or skimming Flushing bay attempting desperately to fly ----also Carbon brakes are far more efficient then the older alloy ones ---
however, I stress only in the case of EFATO -- I don't care about tires and such a those speeds and all the nonsense warnings are [thankfully inhibited] and all warnings are nonsense at near V1 speeds
---best of luck I am glad that you'll continue consulting and passing your rich aeronautical knowledge down to the next generation ---the 'me generation'--who may have spent more time listening to Misses Tooey [who teaches alot of hooey] than Mr. Davies
sorry I just could not keep my mouth shut -I'm one of the
Pugilistic Animus
But regarding the V-5 that would be ok if you're and you know for sure that you ASD limited ---but if you're obstacle limited one may well sink below /at--the NTOFP [especially hot and high where that is more usual]--or-wind up with zero screen height when all of the perf assumptions are hidden from the view of pilots ----I think that one should simply use V1---today's operation 2 crew FMC run FD's are not good places to do such a thing --they gave your generation the performance data in the AFM set to think through such a decision---I don't think a today's operational philosophies permit such a thing to be done safely --believe me --- I do see where you are coming from but without that information it's a crap shoot
One could always use less derate or a lower than max [limiting] AT to increase performance margins although quite frankly I don't think airlines give enough training or data to safely artificially lower V1 as they may end up flying into the side of some ridge or skimming Flushing bay attempting desperately to fly ----also Carbon brakes are far more efficient then the older alloy ones ---
however, I stress only in the case of EFATO -- I don't care about tires and such a those speeds
and all the nonsense warnings are [thankfully inhibited] and all warnings are nonsense at near V1 speeds---best of luck I am glad that you'll continue consulting and passing your rich aeronautical knowledge down to the next generation ---the 'me generation'--who may have spent more time listening to Misses Tooey [who teaches alot of hooey] than Mr. Davies
sorry I just could not keep my mouth shut -I'm one of the
Pugilistic Animus
Joined: Jul 2007
Posts: 350
Likes: 0
From: ***
GlueBAll:
Well, I realize I am not the only one at the airport. But I didn't say I was going to do a backtrack, holding everything up. I think it doesn't make a difference at all, if I am #6 holding at full lenghts or # 6 at the intersection - I will be number 6. And just to have the towercontroller have a nicer picture with aircraft evenly distributed over the various holdshort points is not my job.
When I am late I emphasize working slowly and with a cool head, I have caught myself too many times in the whirlpool of taxiing fast and rushing checklists. I won't do it anymore. So I do have the extra minute to taxi to full lenght.
And yes, I somewhat trust the performance calculations. At least, when done correctly and you still ended up in the grass, they make a pretty good excuse in front of the judge. But if I have a choice, why would I move along the edge of performance? It is legal to takeoff with stopmargin 0, but is it smart?
Nic
Well, I realize I am not the only one at the airport. But I didn't say I was going to do a backtrack, holding everything up. I think it doesn't make a difference at all, if I am #6 holding at full lenghts or # 6 at the intersection - I will be number 6. And just to have the towercontroller have a nicer picture with aircraft evenly distributed over the various holdshort points is not my job.
When I am late I emphasize working slowly and with a cool head, I have caught myself too many times in the whirlpool of taxiing fast and rushing checklists. I won't do it anymore. So I do have the extra minute to taxi to full lenght.
And yes, I somewhat trust the performance calculations. At least, when done correctly and you still ended up in the grass, they make a pretty good excuse in front of the judge. But if I have a choice, why would I move along the edge of performance? It is legal to takeoff with stopmargin 0, but is it smart?
Nic
Joined: May 2007
Posts: 1,415
Likes: 2
From: Europe
At the risk of being boringly repetitive, I wonder why anyone trusts performance calculations, for an intersection departure where the margins are tight.
There are simply too many unknown variables to make any such calculation more than an approximation at best; I mentioned some earlier in an unnecessarily aggressive post. They include the following (with apologies to those who have pointed some out);
And of course, the stopway may not be quite what it's cracked up to be if a heavy aircraft hits it. Not every airport is perfect, but the AIP or equivalent won't say that..
And so on. None is likely to cause problems by itself, but supposing the holes line up one unlucky day?
There are simply too many unknown variables to make any such calculation more than an approximation at best; I mentioned some earlier in an unnecessarily aggressive post. They include the following (with apologies to those who have pointed some out);
The internediate slope from the intersection, perhaps the lowest point of the runway. The max permitted intermediate slope can be well above the overall published net slope.
The true aircraft weight. A loadsheet ramp weight has an accuracy of, let's say, +/- 1 tonne, perhaps more depending on your aircraft type, if we are being brutally honest. The performance data provide for this, but is the allowance enough?
The runway surface. Has it got the desired friction? Was there a recent shower the crew don't know about?
The actual head-wind component during the roll, if it's a bit variable and gusty.
The actual state of the brakes, bearing in mind that the aircraft will probably be stopping with asymetric power. How close to the next check are they?
The actual distances available from the intersection. OK, ATC can usually provide, but didn't someone mention a ruler on the chart?
Can aircraft always be stopped as their Flight Manuals and performance graphs/tables say they can? (Certainly not one I was in at Beirut, on one fairly alarming occasion.)The true aircraft weight. A loadsheet ramp weight has an accuracy of, let's say, +/- 1 tonne, perhaps more depending on your aircraft type, if we are being brutally honest. The performance data provide for this, but is the allowance enough?
The runway surface. Has it got the desired friction? Was there a recent shower the crew don't know about?
The actual head-wind component during the roll, if it's a bit variable and gusty.
The actual state of the brakes, bearing in mind that the aircraft will probably be stopping with asymetric power. How close to the next check are they?
The actual distances available from the intersection. OK, ATC can usually provide, but didn't someone mention a ruler on the chart?
And of course, the stopway may not be quite what it's cracked up to be if a heavy aircraft hits it. Not every airport is perfect, but the AIP or equivalent won't say that..
And so on. None is likely to cause problems by itself, but supposing the holes line up one unlucky day?
Joined: Aug 1998
Aviation Qualifications: ATPL
Posts: 6,623
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From: Ex-pat Aussie in the UK
Just a note that the Kalitta overrun in Brussels was an attempted abort above V1, after a bird ingestion.
Joined: Dec 2003
Posts: 2,349
Likes: 845
From: Tring, UK
Capot,
Pretty much all of these apply equally to the full length...
I notice this becomes a special problem when "margins are tight". In a modern airliner, 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.
If you want to introduce more certainty into the stopping case, then you'll have to 'unbalance' the calculations by forcing a higher flap setting and/or using more power. If you want to be as "safe" as possible, use full power and all available high-lift devices; if you don't do that, then the situation often won't be substantially different from an intersection departure.
Some more thoughts: If it's a longer taxi to the full length (must be, really, or why bother with the intersection?), you're putting energy into the brakes - a significant amount, sometimes - which makes a brake/tyre fire/failure more likely with a high-speed RTO. Another thing is that performance software will often automatically add more flap when optimising a departure using a shorter run, so you might end up with a lower V1 than when using the full length: what everybody wants...
Again, for the third time, I imply no criticism of those who wish to partake of the maximum available tarmac at all times. However, in a technical forum we should be able to discuss the actual physical ramifications of our decision making without taking any of it personally. A question has been asked (and it's turned out to be a goody), so we should try our best to answer it as objectively as possible. (Not that I'm always an innocent in that regard!). "You" in the above text is meant as a generic "you" rather than representing any of the other posters in this thread.
The internediate slope from the intersection, perhaps the lowest point of the runway. The max permitted intermediate slope can be well above the overall published net slope.
The true aircraft weight. A loadsheet ramp weight has an accuracy of, let's say, +/- 1 tonne, perhaps more depending on your aircraft type, if we are being brutally honest. The performance data provide for this, but is the allowance enough?
The runway surface. Has it got the desired friction? Was there a recent shower the crew don't know about?
The actual head-wind component during the roll, if it's a bit variable and gusty.
The actual state of the brakes, bearing in mind that the aircraft will probably be stopping with asymetric power. How close to the next check are they?
The actual distances available from the intersection. OK, ATC can usually provide, but didn't someone mention a ruler on the chart?
The true aircraft weight. A loadsheet ramp weight has an accuracy of, let's say, +/- 1 tonne, perhaps more depending on your aircraft type, if we are being brutally honest. The performance data provide for this, but is the allowance enough?
The runway surface. Has it got the desired friction? Was there a recent shower the crew don't know about?
The actual head-wind component during the roll, if it's a bit variable and gusty.
The actual state of the brakes, bearing in mind that the aircraft will probably be stopping with asymetric power. How close to the next check are they?
The actual distances available from the intersection. OK, ATC can usually provide, but didn't someone mention a ruler on the chart?
I notice this becomes a special problem when "margins are tight". In a modern airliner, 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.
If you want to introduce more certainty into the stopping case, then you'll have to 'unbalance' the calculations by forcing a higher flap setting and/or using more power. If you want to be as "safe" as possible, use full power and all available high-lift devices; if you don't do that, then the situation often won't be substantially different from an intersection departure.
Some more thoughts: If it's a longer taxi to the full length (must be, really, or why bother with the intersection?), you're putting energy into the brakes - a significant amount, sometimes - which makes a brake/tyre fire/failure more likely with a high-speed RTO. Another thing is that performance software will often automatically add more flap when optimising a departure using a shorter run, so you might end up with a lower V1 than when using the full length: what everybody wants...
Again, for the third time, I imply no criticism of those who wish to partake of the maximum available tarmac at all times. However, in a technical forum we should be able to discuss the actual physical ramifications of our decision making without taking any of it personally. A question has been asked (and it's turned out to be a goody), so we should try our best to answer it as objectively as possible. (Not that I'm always an innocent in that regard!). "You" in the above text is meant as a generic "you" rather than representing any of the other posters in this thread.