Should I take the longer runway
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We use up to a 20% reduction in thrust on the 777 and 747 on slippery runways. I am looking at the performance chart right now in the Performance Inflight section called TO2 Slippery runway takeoff, 20% Thrust Reduction, Maximum Reverse Thrust, Weight Adjustment(1000 kg). Similar charts are given for slush/standing water.
If I remember correctly, full thrust seems to be required for windshear conditions on takeoff.
Unfortunately, somebody that I have never heard of before called Piltdown Man has barged onto a decent thread discussing performance with two posts that started with insults about a "poor grasp of safety, performance" and calling people amateurs when it appears that he is actually the one that fits the category.
How about from now on we just stick to professional discussion.
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That is a derate. We have 10 and 20% options although I believe that the setup is company specific with 1% reduction options available possibly to a maximum of 20(and probably after paying Boeing for the performance figures).
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Which brings in the ever spiralling discussion. B737NG: 22k, 24k 26k 27K are all full power. If the engine is rated 27K, and you can make an acceptable performance calculation, then a 22k takeoff is allowed as this can be considered full power; but not an assumed temp takeoff as well. (some a/c have only 22K engines anyway). Somewhere in the thrust graph 27K + assumed temp = 22K. There are some authorities that do not allow operators with >22K engines to use derates: everything is assumed temp from the max available power. Thus, on a contaminated runway, or for any other of the relevant reasons, no matter what the ATOW, you blast off with a huge surplus of power. We know about the effect of power on VMCG & VMCA; we know about the power pitch couple - more apparent with light a/c - we know about the exaggerated swing this would give with an engine failure at V1 and a long pause while you wait for Vr.
Question. Is this method of takeoff thrust calculation a good idea or not? Especially on a contaminated runway?
Question. Is this method of takeoff thrust calculation a good idea or not? Especially on a contaminated runway?
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In order to reduce weight from close to MTOW (Maximum Take Off Weight) I would taxi to the longer runway cause it is far away and use Flex Take Off (It's de-rated thrust but called like this in Airbusses) if needed otherwise to reduce a bit more weight TOGA (Take off - go around power) which puts maximum take off thrust available.
If the RWY is let's say 3300 meters and I am close to full weight with the Airbus A320 I would choose TOGA if bad conditions such as rain, etc.. or Flex Detent in good conditions. Longer RWY's are better as you most of the time do not need to brake maximum or close to maximum in order to stop incase of an aborted take off. Actually it's more "recommended" to use the RWY that is said in the flight plan paper.
Taking off with MTOW almost always causes structural damage.
If the RWY is let's say 3300 meters and I am close to full weight with the Airbus A320 I would choose TOGA if bad conditions such as rain, etc.. or Flex Detent in good conditions. Longer RWY's are better as you most of the time do not need to brake maximum or close to maximum in order to stop incase of an aborted take off. Actually it's more "recommended" to use the RWY that is said in the flight plan paper.
Taking off with MTOW almost always causes structural damage.
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Taking off with MTOW almost always causes structural damage.
Surely you mean max structural takeoff weight. But is it not the case the a/c owe designed with margins in their design? Max structural weight will have a buffer before the undercarriage collapses. For those who operate long-range cargo flights to squeeze every cent/penny out of the flight will clock up huge numbers of max structural takeoffs. It is a very sweeping statement.
Surely you mean max structural takeoff weight. But is it not the case the a/c owe designed with margins in their design? Max structural weight will have a buffer before the undercarriage collapses. For those who operate long-range cargo flights to squeeze every cent/penny out of the flight will clock up huge numbers of max structural takeoffs. It is a very sweeping statement.
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Longer is Better
Short of some obvious reason to use the shorter runway, in the case you describe I would almost ALWAYS use the longer one. Why? More runway gives you more options if/when something goes sour. I'm a huge fan of more options and yes, I'd pick the longer rwy in in a light airplane, for the same reasons. I've never been in such a rush that 'buying' more options was not possible. If pressure to take off quickly becomes excessive, perhaps it is a great day to NOT go flying.
I've kinda scanned through 4 pages here.
If taxi time differences are negligible ( and I were PIC) I would always go for the longer runway.
Why?
All the unforeseen stuff that the performance doctors didn't think about.
The day all the holes in the cheese line up.
Finding out the airplane won't fly at Vr is not a good thing.
Cockpit transcript released from jet crash that killed Lewis Katz, 6 others - philly-archives
https://en.wikipedia.org/wiki/2008_S...arjet_60_crash
The above are all examples of things that "shouldn't happen" but they did.
Trim is not supposed to freeze either..had that happen...in a CJ2
Longer is better..if in doubt..ask y'er wife..
If taxi time differences are negligible ( and I were PIC) I would always go for the longer runway.
Why?
All the unforeseen stuff that the performance doctors didn't think about.
The day all the holes in the cheese line up.
Finding out the airplane won't fly at Vr is not a good thing.
Cockpit transcript released from jet crash that killed Lewis Katz, 6 others - philly-archives
https://en.wikipedia.org/wiki/2008_S...arjet_60_crash
The above are all examples of things that "shouldn't happen" but they did.
Trim is not supposed to freeze either..had that happen...in a CJ2
Longer is better..if in doubt..ask y'er wife..
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If taxi time differences are negligible ( and I were PIC) I would always go for the longer runway.
I'm not disagreeing with you, but you invite the questions:
1. You are taxying // to the RWY an there is a queue at the threshold Hold. ATC asks if you can accept the intersection for a no-delay departure. Company SOP is to calculate performance for intersection, but it is captain's discretion to use it or not. YES/NO? What have you done; ever?
2. The runway entry point requires a back-track for full length. Company SOP is to calculate performance for the entry point, but captain's discretion to use it or full length. Busy period on finals. Immediate takeoff at entry point or wait for 3 landings and then back track. YES/NO? What have you ever done?
3. Various airports have the apron near one end of the single runway: let's say the southern end. You wish to depart to the north. The wind is 7kts on the runway from south. Runway is your choice. Do you calculate for a 10kt tailwind, short taxi, short SID? Or calculate for zero headwind, long taxi and long SID? Oh, and you're late? What have you ever done?
I'm not disagreeing with you, but you invite the questions:
1. You are taxying // to the RWY an there is a queue at the threshold Hold. ATC asks if you can accept the intersection for a no-delay departure. Company SOP is to calculate performance for intersection, but it is captain's discretion to use it or not. YES/NO? What have you done; ever?
2. The runway entry point requires a back-track for full length. Company SOP is to calculate performance for the entry point, but captain's discretion to use it or full length. Busy period on finals. Immediate takeoff at entry point or wait for 3 landings and then back track. YES/NO? What have you ever done?
3. Various airports have the apron near one end of the single runway: let's say the southern end. You wish to depart to the north. The wind is 7kts on the runway from south. Runway is your choice. Do you calculate for a 10kt tailwind, short taxi, short SID? Or calculate for zero headwind, long taxi and long SID? Oh, and you're late? What have you ever done?
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B2N2 - Would a longer runway have really helped in this event? The choice of runway depends on what your company's requirements are. If they say flex at any cost, then so be it. But if are going to run out of duty time, run out of MEL time, miss your slot, run out of HOT, miss connections, hit noise fines for late arrivals then maybe not. To decide, you need more information than just runway length.
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If the RWY is let's say 3300 meters and I am close to full weight with the Airbus A320 I would choose TOGA if bad conditions such as rain, etc.. or Flex Detent in good conditions. Longer RWY's are better as you most of the time do not need to brake maximum or close to maximum in order to stop incase of an aborted take off. Actually it's more "recommended" to use the RWY that is said in the flight plan paper.
Taking off with MTOW almost always causes structural damage.
Taking off with MTOW almost always causes structural damage.
I'm missing the whole "taking off at MTOW almost always causes structural damage" point though...
If taxi time differences are negligible ( and I were PIC) I would always go for the longer runway.
I'm not disagreeing with you, but you invite the questions:
1. You are taxying // to the RWY an there is a queue at the threshold Hold. ATC asks if you can accept the intersection for a no-delay departure. Company SOP is to calculate performance for intersection, but it is captain's discretion to use it or not. YES/NO? What have you done; ever?
2. The runway entry point requires a back-track for full length. Company SOP is to calculate performance for the entry point, but captain's discretion to use it or full length. Busy period on finals. Immediate takeoff at entry point or wait for 3 landings and then back track. YES/NO? What have you ever done?
3. Various airports have the apron near one end of the single runway: let's say the southern end. You wish to depart to the north. The wind is 7kts on the runway from south. Runway is your choice. Do you calculate for a 10kt tailwind, short taxi, short SID? Or calculate for zero headwind, long taxi and long SID? Oh, and you're late? What have you ever done?
I'm not disagreeing with you, but you invite the questions:
1. You are taxying // to the RWY an there is a queue at the threshold Hold. ATC asks if you can accept the intersection for a no-delay departure. Company SOP is to calculate performance for intersection, but it is captain's discretion to use it or not. YES/NO? What have you done; ever?
2. The runway entry point requires a back-track for full length. Company SOP is to calculate performance for the entry point, but captain's discretion to use it or full length. Busy period on finals. Immediate takeoff at entry point or wait for 3 landings and then back track. YES/NO? What have you ever done?
3. Various airports have the apron near one end of the single runway: let's say the southern end. You wish to depart to the north. The wind is 7kts on the runway from south. Runway is your choice. Do you calculate for a 10kt tailwind, short taxi, short SID? Or calculate for zero headwind, long taxi and long SID? Oh, and you're late? What have you ever done?
As your options pose a significant increase in taxi or otherwise taking a significant delay where we could just be departing now (time costs money too, even if operational costs where not in the "initial question"), I'd be more than happy to depart now from an intersection, or the shorter runway for that matter, if the performance numbers add up and no other significant factors come into play. Sitting 5, 10 or 15+ minutes just to take a longer runway just doesn't make any sense to me if there's an option to depart now with enough safety margin. Plus, missing a slot, leaving flight stranded because of duty time expired and that sort of things are far more expensive than using TOGA or a lower flex for one single flight.
I'm all for efficiency if safety isn't impacted. If the numbers are correct and no other factors come into play, all of the 3 cases which RAT 5 poses are acceptable to take. It's just not possible/feasible/sensible to always take the seemingly safest course of action on a commercial aircraft when there are other just-as-safe options to take.
B2N2 - Would a longer runway have really helped in this event? The choice of runway depends on what your company's requirements are. If they say flex at any cost, then so be it. But if are going to run out of duty time, run out of MEL time, miss your slot, run out of HOT, miss connections, hit noise fines for late arrivals then maybe not. To decide, you need more information than just runway length.
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1. airport has // runways. The longer one has been designated for landing and the duty takeoff runway is the shorter, but adequate one. The first runway to arrive at is the duty takeoff runway. There is no landing traffic. You are in sequence for takeoff. Which do you use?
2. airport, for local reasons, is using one runway direction. The wind shifts and results in 8kts tail wind. You have performance for 10kts. What do you do? Use the duty runway or request the reciprocal with the incurring delay?
Safety: a good concept. Remember the days before 2 engine ETOPS. Shock horror. Why would you do this when there are 3 & 4 engine a/c around. Then 90mins ETOPS, then 120, now 180. Not saying it's comfortable, but......once you leave the 60 mins your senses become very alert; like the first time I crossed open water in a single piston. OMG, the engine would quit as soon as I left gliding distance.
But here we are, possibly the end of B747 in sight and the world reverts to twins everywhere. Are guys requesting non-ETOPS routes or flying the 180mins routes? Similar philosophy. You can take the argument of safety to any length and decide to stay in bed.
2. airport, for local reasons, is using one runway direction. The wind shifts and results in 8kts tail wind. You have performance for 10kts. What do you do? Use the duty runway or request the reciprocal with the incurring delay?
Safety: a good concept. Remember the days before 2 engine ETOPS. Shock horror. Why would you do this when there are 3 & 4 engine a/c around. Then 90mins ETOPS, then 120, now 180. Not saying it's comfortable, but......once you leave the 60 mins your senses become very alert; like the first time I crossed open water in a single piston. OMG, the engine would quit as soon as I left gliding distance.
But here we are, possibly the end of B747 in sight and the world reverts to twins everywhere. Are guys requesting non-ETOPS routes or flying the 180mins routes? Similar philosophy. You can take the argument of safety to any length and decide to stay in bed.
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I do see 777's in Istanbul taking off southbound when runway 35L/R is the runway in use for takeoff. But perhaps all of them do not meet their performance requirements.
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I don't see any difference between using any of the the runways.The longer one or the shorter one.
The Fact that I am using Flex/ATM on the longer runway means that I am going to consider the entire length to be usable in case of a reject. Hence giving it a time line... Longer runway.. Lesser thrust... More Time to V1.. More Time to Vr... More Time to Get airborne... The amount of runways required to stop in-case of a reject on a longer runways will not necessarily be more.
Shorter Runway .... More thrust.... Less time to V1... less time to Vr... now incase I reject... I have lesser speed to bleed but lesser runway as well.
My performance Characteristics on both the runway short or long are going to be the exact same for the simple reason that I have used ATM/Flex on the longer runway. Some where on the first page some one wrote about the actual density and temp that being the only +ve side of ATM/Flex in terms of performance and Abslutely nothing else (Disregarding cost)
Also company specific performance usually has optimized V1.. to use the full runway ..Puting it simply just because you have a longer runway does not mean you can liftoff heavier.The longer the runway the more are the chances of an obstacle infringement. OTHH (Doha Qatar) rwy 34R/L have obstacles, in the case one would use improved V1 speeds for takeoff the weight penalty is more than unimproved v1.
The Fact that I am using Flex/ATM on the longer runway means that I am going to consider the entire length to be usable in case of a reject. Hence giving it a time line... Longer runway.. Lesser thrust... More Time to V1.. More Time to Vr... More Time to Get airborne... The amount of runways required to stop in-case of a reject on a longer runways will not necessarily be more.
Shorter Runway .... More thrust.... Less time to V1... less time to Vr... now incase I reject... I have lesser speed to bleed but lesser runway as well.
My performance Characteristics on both the runway short or long are going to be the exact same for the simple reason that I have used ATM/Flex on the longer runway. Some where on the first page some one wrote about the actual density and temp that being the only +ve side of ATM/Flex in terms of performance and Abslutely nothing else (Disregarding cost)
Also company specific performance usually has optimized V1.. to use the full runway ..Puting it simply just because you have a longer runway does not mean you can liftoff heavier.The longer the runway the more are the chances of an obstacle infringement. OTHH (Doha Qatar) rwy 34R/L have obstacles, in the case one would use improved V1 speeds for takeoff the weight penalty is more than unimproved v1.
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Thanks guys, that was exactly what my original question was about. Like I already said, skip the considerations for time to taxi/duty day and all the other endless excuses. The question is based on using the max derate and ATM on each runway length.
Subject to confirmation, may feel better to use the longer runway but now you are reducing the thrust even more for the takeoff. So assuming that you are not at maximum derate/atm, it appears that there is no more margin for an RTO or accelerate-go as there was on the shorter runway.
Then again, if it is a really long runway, then perhaps it is safer.
Is this correct?
Subject to confirmation, may feel better to use the longer runway but now you are reducing the thrust even more for the takeoff. So assuming that you are not at maximum derate/atm, it appears that there is no more margin for an RTO or accelerate-go as there was on the shorter runway.
Then again, if it is a really long runway, then perhaps it is safer.
Is this correct?
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Totally agree with bucks raj
I can't see any improvement into a "safety margin" choosing the longer runway while using assumed temperature, instead of shorter rwy/full trust. Maybe, since you are not field limited, you will get a higher V1 for the longer runway, and that could be useful, but once in the air, in both situations the airplane will perform equally.
But I also agree that taking the longer one and applying full thrust could be the best option, if you really want to improve your safety margin, since you are at MTOW.
Regarding to cost effectiveness, you should consider the longer taxi time to the longer runway, and maybe request more taxi fuel if the longer runway is not the runway considered in your flight plan, to not compromise your trip fuel, and requesting extra fuel at the last minute can lead to a little delay.
I can't see any improvement into a "safety margin" choosing the longer runway while using assumed temperature, instead of shorter rwy/full trust. Maybe, since you are not field limited, you will get a higher V1 for the longer runway, and that could be useful, but once in the air, in both situations the airplane will perform equally.
But I also agree that taking the longer one and applying full thrust could be the best option, if you really want to improve your safety margin, since you are at MTOW.
Regarding to cost effectiveness, you should consider the longer taxi time to the longer runway, and maybe request more taxi fuel if the longer runway is not the runway considered in your flight plan, to not compromise your trip fuel, and requesting extra fuel at the last minute can lead to a little delay.
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Yes there is a significantly lower chance of an engine failure at lower thrust. The damage to the engine is exponential(ish) with temp.
http://www.b737.org.uk/assumedtemp.h...rust_Reduction
http://www.smartcockpit.com/docs/CFM...pport_B737.pdf
About slide 50 onwards
http://www.b737.org.uk/assumedtemp.h...rust_Reduction
http://www.smartcockpit.com/docs/CFM...pport_B737.pdf
About slide 50 onwards
Last edited by Tourist; 23rd Aug 2016 at 10:44.