using full length of rwy for t/o

[downwind]

What are people's impressions of using full length rwy departures, instead of intersection departures for jets such as the 737/A320 etc....? is it good airmanship or not really needed? (the a/c is not at MTOW and we have a long rwy, no performance limits)

[Admiral346]

The question is: Why would you want to go from the intersection?

To save time? Are you late already? Are you trying to avoid turning back to get deiced again (not all too likely in Australia)?

Here in MUC, my base, controlers like to put you on an intersection, but I decline every time, eventhough my stopping margine might be around 1000m. Why would I give that away, just to make a controller happy? I even decline if it makes me #1 ahead of three others and I am late already. I just cannot find a reason to justify giving up a safety margin I am so glad to have . when flying the A340 almost every takeoff was with a stopping margin close to 0, so the extra meters my CRJ gives me on most RWYs are gladly accepted.

No need to rush, better be safe...

Nic

[enicalyth]

The questioner specifically asks about lightly loaded B737/A320 not a heavy A340. At Brisbane for example the domestic and international terminals are considerably spaced apart. May a little light F70 departing Rwy 01 for Norfolk Island not legitimately trundle to "domestic" intersection A7 rather than "international" A9? Let's say the F70 insists on coming down to A9 and from your lofty vantage point in the A340 you see him rotate after 1500 metres with fully 2000 metres remaining thus delaying you and three B777's behind you. You need the full runway, and he doesn't. Do you congratulate him for the extra three minutes of fuel it has cost you because your take-off run will now be that little bit shorter?

Is it not the case that both aircraft and airports are designed to accommodate a number of options that are both safe and consonant with good airmanship?

I wonder under which pseudonym ssg will now reply

[FullWings]

I find it interesting that some pilots won't consider intersection departures (not a criticism, just an observation) yet at the same time are quite happy to perform derated thrust takeoffs. Off wet runways as well!

Modern performance software programs/FMCs have the effect of turning many TOs into balanced field scenarios, leaving you back where you started.

Yes, runway behind you, fuel in the bowser and all that sort of thing but you have to ask what you're actually going to use that extra tarmac for and how likely is it you're going to need it. Tempted by a post-V1/Vr reject? Put it back down after you've left the ground? Taking these sort of options usually ends in a crash, statistically speaking. Sometimes extra choices are not helpful and may lead to bad decision making.

If it's going to save fuel/time, etc. then I'm happy to go from wherever, if the figures say yes. If there's nothing to gain, then full length starts to look attractive.

[GlueBall]

Admiral346 . . . your point is well taken and easily understood. It's always ideal to be able to land and to take off using full length on the longest runway at every airport.

But your CRJ is not the only airplane on the airport. And it's not just a matter of eroding your "extra-extra" safety margin, it's also a matter of practical reality. Commensurate with your intersection approved runway analysis, with your CRJ jet on a 4000 meter pavement. . . are you suggesting that you need the extra 1500+ meters beyond your V1 accelerate-stop distance to stop . . . ? :confused:

[Nightrider]

In our operation (B737) we do not always have performance charts for all intersections, full RWY required in these cases.
With full RWY available I feel a bit more comfortable if the take-off is just at minimum legal separation behind a 'heavy' as a case of N-1 will give me a chance to deal with it while not immediately having to go through some leftovers of the still present wake turbulences of the bigger brothers and sisters.
We do not derate, we use assumed temperature; the full runway allows mostly for a nice reduction and it helps to keep the engines a bit cooler.
The longer runway gives me also a bit of a higher V1/Vr as a result of improved speeds, something which may give you the necessary extra margin for the understatement of todays passenger weights.
And if you do not have to use the full RWY for an RTO, it helps me to stay cooler as well.

Do we get a discount for intersection take-off? No, but you may be asked after parking in the gravel why you accepted it.

The RWY behind you is as useless as ....

In a reasonable way, full length is my option.

[Pontius]

you may be asked after parking in the gravel why you accepted it.

Why would you be asked such a question? Do your managers not understand the concept of balanced field performance calculations? If the figures come out to max derate and max assumed temperature from the intersection then you'll either get airborne and avoid the nasty things on the climb out or you'll stop before the gravel. Either that or I've misunderstood performance all along!

This concept of 'just in case' can be absolute nonsense, especially statements like Here in MUC, my base, controlers like to put you on an intersection, but I decline every time. Okay, so it's your perogative to decline but why if it's perfectly safe? Why not try to make up some of the time when you're late and, thereby, keep those people behind you a bit happier by getting to the destination less late? Why not cause less inconvenience to your fellow pilots if you're in a similar situation to that mentioned in BNE? I'm not for one moment advocating shortcuts or caning the engines to achieve an intersection take-off but, in a situation like MUC, with runways to the moon, refusing an intersection take-off and inconveniencing pax, pilots and controllers just because you'll have even more tarmac in front of you following an RTO is just silly. If you're THAT worried about margins then why derate at all and I do hope you'd never use less than max take-off flap. You can never be too careful eh! Full thrust and flap 15 for all 737s on a runway 4000m long......did someone mention professional pilots or is no-one confident enough in their understanding of performance that they're more scared of lawyers and the 'just in case' monsters?

[Checkboard]

You either trust your performance calculations, or you don't. I'll take an intersection every time, if it saves me any time at all - and the safety of my flight is guaranteed by my performance calculations.

If you won't accept an intersection on a 4000m runway, does that mean you refuse to fly to any destination with a runway shorter than 4000m? :cool:

[411A]

Used intersection departures many times with large piston/turbopropellor types (Lockheed Electra, especially), but don't fly a light jet, only very heavy ones, so full length is required.
However if light, and performance data available, seems reasonable to me, conditions permitting.
However, don't paint yourself into a corner in doing so.

[Henry VIII]

However if light, and performance data available, seems reasonable to me, conditions permitting.:ok:
e.g. - heavy acft on a short leg with few fuel... why not ?

enycalith :ok:

[Piltdown Man]

The T/L - Climb tables is where you justify an intersection take-off. If you find yourself in the gravel, you will say that the book issued by the company for the aircraft you are flying said you could do so. That is all the justification you need. Similarly, taking minimum fuel. If you follow your flight planning rules and come up with figure X, how much more makes it safer? One tonne, five or is an arbitary amount of time added instead? And what is the minimum underload you are prepared to accept on a loadsheet? Zero or would you like more? And where would you like the CofG. Within limits or do we want to add some extra margin here as well? Say 2% MAC or would you like more?

The days of the wet finger in the air/palm readers/fortune tellers and lucky rabbit's (unlucky bunny) foot have gone. To make it totally safe, call in sick!

PM

[Private jet]

All of the salient technical points have been covered already so i won't repeat, but a good homily i was taught is......

The three most useless things in aviation are;
1 Runway behind you
2 Sky above you
3 Fuel still in the bowser

[Permafrost_ATPL]

From Checkboard: You either trust your performance calculations, or you don't

On the head. If you abort prior to V1, you will stop before the gravel. If you don't believe that, why do you go to work?

P

[Pontius]

The three most useless things in aviation are;
1 Runway behind you
2 Sky above you
3 Fuel still in the bowser

It's such a worn out quotation and clearly has very little relevance to modern commercial aviation. You only ever hear it in the bars of flying clubs from the resident 'expert', who likes to say it loudly because he thinks it's so clever and nobody else has ever heard it before.

1. Runway behind you is not useless if you're using balanced field calculations. Something the Cessna expert in the club bar will have little clue about.

2. If sky above me is useless that means I should be flying right up there where the stall and Mmo are coincident. Maybe I'm just being cautious but I really don't think that's the best place for an airliner to hang out, especially with that nasty turbulence stuff that goes 'bump' in the air and suddenly sends your speed one side or the other of the 'hockey sticks'. Having the advantage of height (and, therefore, potential energy) is good for a fighter pilot and it's jolly nice to have if you've lost all your means of propulsion but to advocate the sky above as useless is just trite waffle.

3. Fuel in the bowser. Well, need I say very much at all? If you think getting airborne every time with full tanks in an airliner is the way ahead then (a)you didn't pay too much attention in class and (b)your airline is not going to be around too long.

As you can tell, I'm not too impressed by such a worn-out cliche that is bantered around by people who clearly have not thought it through. You don't HAVE to laugh when the boring old fart in the left seat says it for the 20th time you know :)

[Capt Claret]

If I used full length at my home port, most departures would be delayed because back tracking the runway is required, in either direction.

If I used full length at a frequent port, I'd have to cross two runways to get to one threshold, and one runway to get to the other, with potential delays, all fo no real increase in safety.

[Private jet]

Pontius, or should that read "Pompous"....

With reference to your points, i agree fully with what you say, its all basic aviation knowledge. As i stated in my previous post there was little to add to what has already been discussed. You have interpreted the expression too literally, these days its more symbolic of adopting a cautious approach to things. I was merely trying to point out (in an obviously unsuccessful way) that I personally like to use extra safety margins whenever it is appropriate, and available to do so. I fly a nice high performance corporate jet and have never been on the limits performance wise for T/O, cruise or landing so perhaps i am being too cautious...But, unlike you poor airline people, we can go straight to FL450 at max weight in all but high temp conditions (ISA +15 up). Usually we don't go that high though, but theres still a good speed margin up there if we do. Also, in our operation, I can pretty much take as much fuel as i want, I don't have to take what "Mummy" strongly suggests I take and I don't live in fear of a good "spanking" if i take more..........

With reference to the tone of your post.... that phrase about grannies and sucking eggs comes to mind.

Lastly, I really don't care what impresses you or not.

[doubleu-anker]

"Pompous"....

What private jet said is true.

Trouble is today, too much emphasis is placed on the automatics and what is "dictated" by the automatics, that the basics seem to be forgotten.

Why use less runway, when more is available?

Why fly low and fast, when it is safer to fly "high" and fast?

Why take less fuel, when it maybe prudent to take more?

Maybe you are one of those robots, that cant function without a "book" to tell you how to function. Maybe you are one of those pilots, that given a set of figures from a computer printout you would treat them as gospel, without a thought, as to the wisdom of cross checking those figures.

[BelArgUSA]

Full length runway is always my rule. No intersection takeoffs.
I even get upset when a PF wastes 200 meters to "line-up" nicely.
Takes longer...? I do not mind... I am paid for extra time if applicable.
xxx
:ok:
Happy contrails

[Pontius]

With reference to the tone of your post.... that phrase about grannies and sucking eggs comes to mind

Yeah, sorry about that PJ. I re-read my post and it does sound as if I was aiming my comments deliberately at you, which was not my intention. My aim was to address the worn out cliche versus flying modern aircraft in today's commercial market. Clearly my written word is not as precise as is necessary (note to self: must make greater use of 'one' rather than 'you').


Doubleu-anker,

Nah, you'll be glad to know I'm not an automaton who treats computer printouts as gospel. I tend to lean towards the other way of doing things but, in doing so, I make sure I know why I'm trusting the computer when I choose to use it. In other words I try to think about what I'm doing rather than relying on 'that's the way I've always done it' or, even worse, relying on a quotation made way back when the pilots flew in white flying overalls, engines were unreliable and taking less than full tanks wouldn't get one across the English Channel.

Why use less runway, when more is available?

Why fly low and fast, when it is safer to fly "high" and fast?

Why take less fuel, when it maybe prudent to take more?


The use of less runway has already been discussed in this thread. There are, of course, times when I would use full length (particularly when you get to contaminated performance which, let's face it, is a best guess anyway). What I am saying is you don't ALWAYS need to use it, hence my comment regarding runway behind you being 'useless'. If, for instance, BelArgUSA wants to use the full length then that's fine. He'll have his own reasons for doing so but they'll hopefully be based on something more scientific and knowledgeable than an out-of-date saying.

Who said anything about flying low? I would rather cruise at the optimum cruise altitude. Yes, I know, silly old me using computers again to optimise the operation of my aircraft, thereby saving fuel and standing more chance of keeping my job as my airline stays afloat. What I said is the saying is nonsense regarding sky above you being wasted. That's not optimum operation that's operating at the ceiling, which I don't think is a good idea.

And as for fuel, do I really need to expand? Again, did I mention never taking extra fuel? There will always be occasions when more fuel is 'prudent' and I have no qualms whatsoever about loading it. However, I will (again) use those pesky flight planning computers and all the means at my disposal to ensure that I take a sensible amount extra and certainly do not subscribe to the 'load a bit for Mum' mentality. It may not be quite as much a concern in the Middle East but it certainly makes my job more secure if all the company pilots think about why and how much extra fuel they are going to carry, as opposed to the unthinking cliche which tells us that fuel left in the tanker is wasted :rolleyes:

[cribble]

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.

The move will probably play hell with domestic ops (next sector) on-time departures but does not worry the long-haulers.

[FullWings]

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... :)

[BelArgUSA]

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.
:eek:
Happy contrails

[FullWings]

...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.
BelArgUSA,

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...

[Musket90]

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.

[Permafrost_ATPL]

Do you have links/citations for any of the "many" above?

I second that motion! Will all respect to the venerable BelgArgUSA, I would really want to see figures to believe that decisions to abort prior to V1 have resulted in many overruns. My gut feeling is that most abort overruns can be linked to other factors, such as attempts to takeoff on contaminated runway, not having full power (without noticing until it's too late), aborts AFTER V1, overweight takeoffs, excessive tailwind, worn-out brakes, incorrect reject technique, etc.

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

[doubleu-anker]

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.

[BelArgUSA]

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
:8
Happy contrails, always.

[GBALU53]

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.

[doubleu-anker]

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.

[Permafrost_ATPL]

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 :ok:

P

[Capot]

and the safety of my flight is guaranteed by my performance calculations.Well actually, not quite, the calculations you're talking about were largely done by someone else.

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".

[framer]

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.

Definately because of runway incursions. Two incursions happened last year , both between Link carriers and both at the angled runway intersections. It is the angle that is seen as the problem, ie the a/c lined up in front of an a/c landing due to the captain having to turn head so far to check that the runway is clear.Obviously there was a lot more to it than that (radio transmissions over-lapping, ATC elements etc). But that is one thing they have done to mitigate the risk. If the intersection is not angled, you can still use it.

[Pugilistic Animus]

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:eek: 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:ugh:

sorry I just could not keep my mouth shut -I'm one of the :8

Pugilistic Animus:)

[Tmbstory]

Congratulations and well done.

Enjoy!

Tmb

[Bob Lenahan]

In the 60's and 70's UAL's poilcy was that all available runway will be used for takeoffs. No telling what they're doing today.
Bob.

[Admiral346]

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

[Capot]

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);
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.)

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?

[Checkboard]

Just a note that the Kalitta overrun in Brussels (http://aviation-safety.net/database/record.php?id=20080525-0) was an attempted abort above V1, after a bird ingestion.

[Pugilistic Animus]

Checkboard, the report states "around V1" quite different...

PA

[FullWings]

Capot,

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?
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. :)

[742]

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.

[Northbeach]

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”.

[misd-agin]

"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.

[Arfur Dent]

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.:ok:

[Rwy in Sight]

So from reading this thread my understanding is the use of full length mainly preferred just to increase the safety margin for a RTO?

Rwy in Sight

[Capot]

Fullwings

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.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?

[FullWings]

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 maximise safety and use the same - higher - power setting you would have used from the intersection, but taking the full length?"
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.

I'm not sure I really buy that. Most of the unknown variables are still present in the calculation.
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?!?)