smartt1982 From United Kingdom, joined Nov 2007, 107 posts, RR: 0 Posted (3 months 2 weeks 1 day 4 hours ago) and read 3725 times:
Hello,
Just a question I want to put out to pilots and performance engineers alike, or anyone else with any input for that matter.
Besides company SOPs and of course Aircraft weight, if the numbers in your performance charts say that you can take off from intersection X and it makes sense to do it, what are the reasons that you would not do it?
I only have about 2000 Hours as a co-pilot on the 737NG but my understanding is if the charts say you can, why not? Don't get me wrong at the end of the day, CRM or not, it is the captains decision as long as it is safe, that is what it is going to be. But sometimes I have flown with captains who are totally against ever taking an intersection take off and these captains are generally the most experienced I have ever flown with, with thousands of hours flying different aircraft over the years, there must be a reason for this rationale!
Unless for exceptional reasons you are not going to try and start stopping the aircraft if you have already hit or gone past V1. The figures calculated for an intersection tell you that, if you initiate a stop at the correct point and providing you have calculated as well as executed everything correctly you should stop within the distance left on the runway. Does the rationale of not taking an intersection give you more time, you still have V1 etc
Another point I like to ask or clarify about, is that I happened to be watching a cockpit DVD and prior to lining up on the runway the crew confirmed with each other that the V speeds were based on the limits of the ASDA. Now I am aware that V speeds are calculated for the more limiting of either the stop or go case, I think it is good situational awareness when planning your performance to discuss or be aware of this but I felt that it was completely unnecessary when lining up on the runway, as in any case if something happens before V1 and the PIC decides to stop, it does not matter what the V Speeds were based on, the pilot will do everything exactly the same, that background I don’t think should have any input on deciding to stop the aircraft in an emergency or not, if this was the case.
Any thoughts or view on that would be greatly appreciated
Mir From United States of America, joined Jan 2004, 17876 posts, RR: 59 Reply 1, posted (3 months 2 weeks 1 day 3 hours ago) and read 3699 times:
Quoting smartt1982 (Thread starter): Besides company SOPs and of course Aircraft weight, if the numbers in your performance charts say that you can take off from intersection X and it makes sense to do it, what are the reasons that you would not do it?
Noise abatement is a big one. But that's generally dictated by the airport, and ATC will know not to let people go off from an intersection.
It really comes down to the runway behind you being pretty useless. RTOs are a big deal - sure, you may say you have the performance to do one in a certain span of runway, but that's based on excellent reaction time by the crew (which we all think we have, but the heat of the moment isn't the time to find out), a fully functioning aircraft with excellent brakes (which we might not have - again, the heat of the moment isn't the time to find that out), etc. So I can understand why some people might choose not to do it.
I'll take an intersection departure, but only if the runway available is significantly longer than the distance I require, and only if the runway is dry (I might amend that if the airport is using intersection departures for traffic flow purposes, but then I'll bump up the distance I feel comfortable with).
-Mir
7 billion, one nation, imagination...it's a beautiful day
Quoting Mir (Reply 1): It really comes down to the runway behind you being pretty useless.
I like to have more margin on my take of. Sure on a 4400m long runway it doesn't matter if I take off from the 4000m point. But the shorter the runway, the closer it gets.
And the longer the runway, the higher your deration can be (considering terrain is not a factor) and that reduces the engine thrust, thus lower engine failure risk...
Quoting smartt1982 (Thread starter): crew confirmed with each other that the V speeds were based on the limits of the ASDA.
We don't do that. We just confirm we are on the correct runway, correct engine thrust (deration), flap setting...
The reasons are as many and varied as there are pilots making the decision. Sometimes the airport (or other outside agency) will make that decision for you. For example, at DFW ATC (as of a couple of years ago) began requiring 3 minutes behind the "heavy" departure if you request the intersection --no exceptions and that includes the parallel runway departures. Previous to that we could use 5 mile separation. Today, nobody asks for an intersection departure when ANY plane is using full length.
Quoting smartt1982 (Thread starter): Does the rationale of not taking an intersection give you more time, you still have V1 etc
Obviously, yes. V1 isn't just based upon Go/Stop criteria. It is also limited by rotation speed (you don't stop after you've rotated). At 13,000' long, domestic flights from KDFW will always have V1 based upon rotation speed.
Quoting smartt1982 (Thread starter): but I felt that it was completely unnecessary when lining up on the runway, as in any case if something happens before V1 and the PIC decides to stop, it does not matter what the V Speeds were based on, the pilot will do everything exactly the same, that background I don’t think should have any input on deciding to stop the aircraft in an emergency or not, if this was the case.
Your logic is undeniable.... and true. The only reason I can think of for knowing the basis of V1 would be that the actual DECISION is made BEFORE reaching V1. Remember, V1 is supposed to be an ACTION speed, not a DECISION speed. When I am truly "runway limited" (i.e. KSNA) my actual DECISION will be made much earlier than when runway/climb is not a factor (i.e. KDFW). But again, as Capt. I have made up my mind when my decision must be made long before entering the runway --and my FO doesn't need to clutter his mind with that info.
*NO CARRIER* -- A Naval Aviator's worst nightmare!
LimaFoxTango From Antigua and Barbuda, joined Jun 2004, 574 posts, RR: 0 Reply 4, posted (3 months 2 weeks 1 day 1 hour ago) and read 3581 times:
At my airline, we cannot use an intersection if we do not have figures published in our RTOW manual for that intersection. So although intersection X might be more runway than what we need, we still have to go full length. It's as simple as that.
You are said to be a good pilot when your take-off's equal your landings.
PapaChuck From United States of America, joined Aug 2010, 112 posts, RR: 0 Reply 5, posted (3 months 2 weeks 1 day ago) and read 3572 times:
I hope I'm not stepping on any toes with this comparison, but I thought I should share.
Funny how you mention older pilots insisting on using full length while younger pilots are willing to accept an intersection departure if the performance numbers line up. I see the same mentality in the ATC world, and I think age does indeed have a lot to do with it. I'm making some broad generalizations here, so please bear with me.
I tend to notice that younger controllers rely more on quick thinking and their reflexes to keep themselves out of trouble. Older controllers, who's reflexes may not quite be what they once were, rely more on experience to avoid getting themselves in to a mess. It helps keep the blood pressure down if you can solve problems before they develop and keep from scrambling at the last second to fix it.
Perhaps the older pilots you mention share the same mentality. The takeoff performance numbers may be adequate, but why not use the whole runway and give yourself a little more time to think should something go wrong. Hesitate for one second, drive the airplane into the EMAS, and see if the chief pilot's first question isn't "Well, why didn't you use full length?"
An RTO at V1 from an intersection may require you to stand on the brakes while full length may only require moderate braking. Saves wear and tear on both men and machine. As already mentioned, runway behind you is useless, so you may as well use it all.
aklrno From United States of America, joined Dec 2010, 435 posts, RR: 0 Reply 8, posted (3 months 2 weeks 11 hours ago) and read 3226 times:
Maybe some tower controller can help me out on this, but wasn't there an issue several years ago of runway incursions as a result of intersection take-offs? IIRC the idea was that if everyone lined up at the same place you eliminated one potential point of failure.
PapaChuck From United States of America, joined Aug 2010, 112 posts, RR: 0 Reply 9, posted (3 months 2 weeks 4 hours ago) and read 3125 times:
The USAir 1493/SkyWest 5569 collision comes to mind. There were some new rules implemented regarding intersection departures at night in the wake of that one.
BA777 From United Kingdom, joined Jun 2001, 2098 posts, RR: 9 Reply 10, posted (3 months 2 weeks 3 hours ago) and read 3093 times:
I agree, if there are RTOWs for it and it´s dry then I´d always go for the intersection if available. However, if the weather and other things like terrain and so on are a big factor then full length is the sensible option. Again, Capts decision at the end of the day...we can only suggest it to them and they are fully entitled to use full length if they so wish.
LONGisland89 From United States of America, joined Jan 2006, 542 posts, RR: 0 Reply 11, posted (3 months 1 week 5 days 1 hour ago) and read 2640 times:
Quoting PapaChuck (Reply 9):
The USAir 1493/SkyWest 5569 collision comes to mind. There were some new rules implemented regarding intersection departures at night in the wake of that one.
Affirmative, in order to use LUAW at night from an intersection, it needs special approval and must be a departure only runway.
zeke From Hong Kong, joined Dec 2006, 6800 posts, RR: 74 Reply 13, posted (3 months 1 week 4 days 7 hours ago) and read 2384 times:
Quoting smartt1982 (Thread starter): if the numbers in your performance charts say that you can take off from intersection X and it makes sense to do it, what are the reasons that you would not do it?
Much the same reasons why I would select TOGA, ignition on, i.e. heavy rain, snow, contaminated runway or windshear reported after takeoff. The other being LWMO conditions, need the taxi lights to get onto the runway, often not available except from the full length.
That being said, almost every takeoff I do, the performance numbers I calculate for every takeoff includes some tailwind and a runway intersection. Many of the airport I fly out of have 3-4 entrances to the runway, and if for example an aircraft needs to run through a MEL procedure at the holding point ATC may offer an intersection for takeoff. We know the data we have already cover us for that scenario, we are right to go.
Quoting smartt1982 (Thread starter): I felt that it was completely unnecessary when lining up on the runway
We do that as SOP for every takeoff, seems unnecessary in CAVOK conditions, absolutely essential in LWMO conditions, if you do it for every takeoff it is second nature. Been many cases over the years of aircraft lining up on the wrong runway or a taxiway, normally this happens in poor conditions or at night.
smartt1982 From United Kingdom, joined Nov 2007, 107 posts, RR: 0 Reply 14, posted (3 months 1 week 4 days 5 hours ago) and read 2333 times:
Quoting zeke (Reply 13): We do that as SOP for every takeoff, seems unnecessary in CAVOK conditions, absolutely essential in LWMO conditions, if you do it for every takeoff it is second nature
Just to clarify but are you referring to checking if you are on the correct runway or something else with regards to your SOP for every take off, what I was referring to which I felt was unnecessary was the crew discussing what the V speed figures were based on, on this occasion the ASDA as they were lining up on the runway
zeke From Hong Kong, joined Dec 2006, 6800 posts, RR: 74 Reply 15, posted (3 months 1 week 4 days 5 hours ago) and read 2330 times:
Quoting smartt1982 (Reply 14): checking if you are on the correct runway
Only the correct runway and intersection, which is silently cross checked with the ILS/ND/FMC. The speeds and intersection are done during the data insertion phase before pushback.
smartt1982 From United Kingdom, joined Nov 2007, 107 posts, RR: 0 Reply 16, posted (3 months 1 week 4 days 5 hours ago) and read 2326 times:
Quoting zeke (Reply 15): Only the correct runway and intersection,
No I completly agree, as we do the same in our company. The crew on this occasion had indeed calulated their figures prior to pushback but I felt it was unnecessary for them to discuss what factor (in this case runway) the V Speeds were based on as they were lining up.
It was the Swiss 340-300 blue ray disc that has been recently released by justplanes.
LONGisland89 From United States of America, joined Jan 2006, 542 posts, RR: 0 Reply 18, posted (3 months 1 week 3 days 19 hours ago) and read 2142 times:
Quoting JD747 (Reply 12):
And what would be the reason or benefits (if any) to take off from an intersection?
The reasons for using intersection departures are numerous and the benefits are directly linked to the airport's layout and/or traffic situation at the time of the LUAW issuance or takeoff clearance. Saving fuel with a shorter taxi isn't the point, the main purpose of an intersection departure is to move traffic efficiently (It's coincidental if it results in a shorter taxi, in the case when it's issued by a controller). It's a pilot's prerogative to request an intersection for that purpose, not the controllers.
-One example would be JFK's use of runway 31L at the KK intersection. 31L departures are often used with 22L/R arrivals/departures and using KK instead of full length eliminates ops where 22R and 31L intersect. [without using KK, spacing would need to be increased for 22R arrivals and runway crossing coordination would have to be accomplished. All equal lower efficiency.]
-Say you have a heavy/757 full length, instead of taxiing a smaller aircraft full length behind the heavy, you can depart a smaller aircraft via an intersection prior to the larger aircraft thus avoiding a wake turbulence delay. Keep in mind, wake turbulence trumps any same runway separation or radar separation that may exist (depending on your facility). [Again, lower efficiency.]
-Say you have a taxiway closure preventing the use of full length and backtracking is unnecessary/impossible. [Not necessarily increasing efficiency but you're using an intersection.]
musang From United Kingdom, joined Apr 2001, 686 posts, RR: 8 Reply 19, posted (3 months 1 week 3 days 7 hours ago) and read 2009 times:
I'm probably nudging the "grey-haired old git" category now, and will instinctively go for the full length. Sure, we have performance data for intersection launches, and sometimes its appropriate for the various ATC reasons mentioned above. However we work in a "cover your a*s/ar*e" environment so I would wonder about being asked "So, captain, why didn't you use the full length?"
If I launched from an intersection, it all went nasty, and I ran off the end by 50 meters I'd be kicking myself. Sure, the chances are minimal, but the basic operating philosophies which dictate the industry's procedures are based on events which most of us will never see outside the simulator.
At home base we are offered an intersection t/o about once in 20 departures, so why routinely set up for a higher thrust setting (engine wear rises exponentially at higher thrust levels) in the hope of a 5% chance of the intersection? Last minute adjustments of the thrust setting + speeds at the holding point are not allowed due to the possible distraction/getting it wrong under pressure.
If there's a line of traffic at the full length, what's the point of taking the int. unless you know you're going to jump the queue? This occasionally happens, but it will be at ATC's instigation and will probably irritate the ones at the full length!
One place we go is about 2500 meters long and we can request a 1900 meter intersection. I probably won't do it unless we're light, late, and there's a significant headwind. Geneva on the other hand is 3900 meters and I'd happily take an int. there because it still gives more runway than just about anywhere else we go. However int. deps. are rare at GVA, I assume because of noise abatement.
Its all to do with gut feeling/instinct/etc. Within our fleet I'm told (by the F/Os) that I'm unusual in going for the full length as a first choice, so I guess I'm in a minority.
JD747 From Spain, joined Nov 2006, 42 posts, RR: 0 Reply 20, posted (3 months 1 week 1 day 10 hours ago) and read 1712 times:
Quoting LONGisland89 (Reply 18): If you push from a gate opposite an intersection, it may make sense to save time and fuel on the taxi to the end of the runway.
PD does it routinely here at YOW.
Quoting musang (Reply 19): The reasons for using intersection departures are numerous and the benefits are directly linked to the airport's layout and/or traffic situation at the time of the LUAW issuance or takeoff clearance. Saving fuel with a shorter taxi isn't the point, the main purpose of an intersection departure is to move traffic efficiently (It's coincidental if it results in a shorter taxi, in the case when it's issued by a controller). It's a pilot's prerogative to request an intersection for that purpose, not the controllers.
-One example would be JFK's use of runway 31L at the KK intersection. 31L departures are often used with 22L/R arrivals/departures and using KK instead of full length eliminates ops where 22R and 31L intersect. [without using KK, spacing would need to be increased for 22R arrivals and runway crossing coordination would have to be accomplished. All equal lower efficiency.]
-Say you have a heavy/757 full length, instead of taxiing a smaller aircraft full length behind the heavy, you can depart a smaller aircraft via an intersection prior to the larger aircraft thus avoiding a wake turbulence delay. Keep in mind, wake turbulence trumps any same runway separation or radar separation that may exist (depending on your facility). [Again, lower efficiency.]
-Say you have a taxiway closure preventing the use of full length and backtracking is unnecessary/impossible. [Not necessarily increasing efficiency but you're using an intersection.]
It's all about the situation
[quote=musang,reply=19]The reasons for using intersection departures are numerous and the benefits are directly linked to the airport's layout and/or traffic situation at the time of the LUAW issuance or takeoff clearance. Saving fuel with a shorter taxi isn't the point, the main purpose of an intersection departure is to move traffic efficiently (It's coincidental if it results in a shorter taxi, in the case when it's issued by a controller). It's a pilot's prerogative to request an intersection for that purpose, not the controllers.
-One example would be JFK's use of runway 31L at the KK intersection. 31L departures are often used with 22L/R arrivals/departures and using KK instead of full length eliminates ops where 22R and 31L intersect. [without using KK, spacing would need to be increased for 22R arrivals and runway crossing coordination would have to be accomplished. All equal lower efficiency.]
-Say you have a heavy/757 full length, instead of taxiing a smaller aircraft full length behind the heavy, you can depart a smaller aircraft via an intersection prior to the larger aircraft thus avoiding a wake turbulence delay. Keep in mind, wake turbulence trumps any same runway separation or radar separation that may exist (depending on your facility). [Again, lower efficiency.]
-Say you have a taxiway closure preventing the use of full length and backtracking is unnecessary/impossible. [Not necessarily increasing efficiency but you're using an intersection.]
rfields5421 From United States of America, joined Jul 2007, 4871 posts, RR: 21 Reply 21, posted (3 months 1 week 1 day 4 hours ago) and read 1652 times:
Quoting LONGisland89 (Reply 11): Affirmative, in order to use LUAW at night from an intersection, it needs special approval and must be a departure only runway.
Even that isn't a guarantee - the Shorts 360 at CDG which had the cockpit sliced open by an Air Liberte MD-83 comes to mind.
bond007 From United States of America, joined Mar 2005, 4926 posts, RR: 9 Reply 22, posted (3 months 1 day 4 hours ago) and read 1091 times:
Quoting KELPkid (Reply 7): Especially in regards to V1 rejected takeoff stopping distance, why not give yourself as much runway length as possible? Seems like a no-brainer to me
Quoting PapaChuck (Reply 5): "Well, why didn't you use full length?"
If it were as simple as using the full runway length available for safety reasons in order to get airborne as soon as possible, we would also takeoff every time at full power (not derated).
Quoting AAR90 (Reply 3): The reasons are as many and varied as there are pilots making the decision
Correct. Not just using (or not using) maximum runway length for safety reasons.
Quoting wilco737 (Reply 2): And the longer the runway, the higher your deration can be (considering terrain is not a factor) and that reduces the engine thrust, thus lower engine failure risk...
I agree that the longer the runway, the more you can use derated thrust, but I'm not sure that directly relates to that particular takeoff being any more risky due to an engine failure. The main reason for using derated thrust is lower ongoing maintenance costs, and longer engine life ... not necessarily safer day-to-day engine operation.
Jimbo
I'd rather be on the ground wishing I was in the air, than in the air wishing I was on the ground!
wilco737 From Greenland, joined Jun 2004, 8009 posts, RR: 83 Reply 23, posted (3 months 1 day 2 hours ago) and read 1059 times:
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Quoting bond007 (Reply 22): I agree that the longer the runway, the more you can use derated thrust, but I'm not sure that directly relates to that particular takeoff being any more risky due to an engine failure. The main reason for using derated thrust is lower ongoing maintenance costs, and longer engine life ... not necessarily safer day-to-day engine operation.
What I meant is: if you use full thrust on an engine, then it is operating close to its limit and the risk that something goes wrong is higher than on full deration.
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Previous to that we could use 5 mile separation. Today, nobody asks for an intersection departure when ANY plane is using full length.
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