EK407 Tailstrike @ ML
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Hi,
sympathy for the crew involved, hope all works out for them.
How about some form of head up display that shows the actual runway ahead, even whilst in LVO conditions. As soon as the aircraft starts its acceleration it shows the approx point of rotation. Could be shaded to accentuate that area. Some form of dynamic principle that varies with wind speed etc.
The company i worked for previously had the weight the aircraft thought it was displayed in the FMC. The V speeds were also displayed, based on that weight. Most of the time it was over the loadsheet weight produced !.
Rgds.
sympathy for the crew involved, hope all works out for them.
How about some form of head up display that shows the actual runway ahead, even whilst in LVO conditions. As soon as the aircraft starts its acceleration it shows the approx point of rotation. Could be shaded to accentuate that area. Some form of dynamic principle that varies with wind speed etc.
The company i worked for previously had the weight the aircraft thought it was displayed in the FMC. The V speeds were also displayed, based on that weight. Most of the time it was over the loadsheet weight produced !.
Rgds.
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In this era of stiff competition and corporate fat boys wishing to pocket more $$ and their shareholder friends looking for incessant profits , do we have here a culture of "just enough thrust for the job " ? Why go with extra thrust when the runway is long and the airplane is light ??? Sometimes, reality and murphys law comes to bite those who become complacent and behind the aircraft computers and the corporate SOP' s , designed to save a dollar and DECREASE safety !!!
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Distance/time check has certain practical difficulties, particularly at night which is most of our ops.
And think about this: even a distance/time check would have to be something calculated for each takeoff to account for weight/rwy etc etc. The key word is "calculated". It would be subject to the same input error.
And think about this: even a distance/time check would have to be something calculated for each takeoff to account for weight/rwy etc etc. The key word is "calculated". It would be subject to the same input error.
If the input data is incorrect, yes it will be in error but that error is exactly what flags an incorrect weight. Instead of monitoring only V1, you monitor V1 and time - if time occurs first, you abort the takeoff. If this happens you know:
- you are below V1 and
- you have have more runway ahead of you than you would have had at V1, because you have been moving more slowly than planned
This wouldn't pick up an error in the runway length however. It also wouldn't flag an incorrect heavier weight being entered, although I imagine that wouldn't be likely to be catastrophic.
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It needs to be something short of V1 where you have time to react. At V1, you're committed.
The only way it can work is if you abort once the time is reached, before V1 - if you wait until V1 and say "that took too long" you don't have the stopping distance that was used for the V1 calculation. If you reach "time to V1" before V1 and continue, you can be sure that at some point you will be below V1 without distance to stop - because the calculated stopping distance is used up by slower acceleration.
And it can't be a rule of thumb - it has to be a hard go/nogo number like V1, output from the V1 calculation.
Another angle.
Lots of discussion about acft weight here, and how it likely to be underestimated. Suggested solution has been to weigh the acft, which is difficult, expensive, and potentially inaccurate.
What about switching to actual pax wt? With the technology available, it would be quite easy to incorporate a weighing system where people checking in stand. That way, pax weights along with ALL the normally un-weighed carry-on baggage is also weighed. No extra time taken, because they are weighed as part of the normal check-in.
Would potentially increase safety, but would almost certainly decrease profit margins. Perhaps the accountants don't want this info?
What about switching to actual pax wt? With the technology available, it would be quite easy to incorporate a weighing system where people checking in stand. That way, pax weights along with ALL the normally un-weighed carry-on baggage is also weighed. No extra time taken, because they are weighed as part of the normal check-in.
Would potentially increase safety, but would almost certainly decrease profit margins. Perhaps the accountants don't want this info?
Carryon weights
With respect to carryon bags, and the lack of weighing, how does an airline manage this?
Ie, you have 100 pax, do they multiply that by 7kg to come up with a "Carry-on-bag-weight" of 700Kg as standard, and include that in the ZFW?
Reason I ask is not everyone will have carryon, and not everyone's carryon will be right at the 7kg limit, thereby offsetting the overweight carryon bags for those that have them...
Ie, you have 100 pax, do they multiply that by 7kg to come up with a "Carry-on-bag-weight" of 700Kg as standard, and include that in the ZFW?
Reason I ask is not everyone will have carryon, and not everyone's carryon will be right at the 7kg limit, thereby offsetting the overweight carryon bags for those that have them...
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Time to v1 NOT suitable!!
Guys,
Although time to v1 looks suitable, it is not!!
It would be if there was a thrust problem. For a weight problem however, you are calculating time to a WRONG v1, with a WRONG thrust. On a short runway, I will not have any indication that I can still stop the aircraft after the WRONG time to the WRONG v1 if I suddenly weigh x tons MORE...
So it is the old saying... BS in, BS out.. and that goes for time to v1 as well...
MR8
Although time to v1 looks suitable, it is not!!
It would be if there was a thrust problem. For a weight problem however, you are calculating time to a WRONG v1, with a WRONG thrust. On a short runway, I will not have any indication that I can still stop the aircraft after the WRONG time to the WRONG v1 if I suddenly weigh x tons MORE...
So it is the old saying... BS in, BS out.. and that goes for time to v1 as well...
MR8
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Reason I ask is not everyone will have carryon, and not everyone's carryon will be right at the 7kg limit,
Go on a Lagos flight and you'll find a whole new description for the term "Big Momma" - and the size of the hand baggage they all carry is almost beyond belief.
Seriously though, what you suggested is pretty close to the industry standard. A standard passenger weight and a standard hand baggage allowance in theory allows for the percentage who will be above standard being offset by the hopefully equal percentage who will be below it. Likewise with the hand baggage. However, as has been suggested above, from daily observation, in many areas of the world, it may be time a new standard weight for both people and what they carry to be accepted and adopted.
Again seriously, any form of 'real time' weighing would be a commercial nightmare, which is why it hasn't been adopted. (Can you imagine the fights between captains and load control?) Boeing, and I'm sure Airbus, allow a generous 'bugger factor' in their performance calculations. I've (purposely) done a takeoff in the sim. in a 777-200 forty tonnes over MTOW with an engine cut (severe damage and separation) at V1 +1. It was curvature of the earth stuff, but we did climb away, if at a very low rate of climb, and managed a full cleanup.
Last edited by Andu; 29th Mar 2009 at 05:36.
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I would argue against abandoning the take-off on the basis of a "rule of thumb" speed check against distance. This photo, at Danang 1965, is of the remains of a USAF B57 that used this methodology. The pilot thought his acceleration wasn't good enough, so he jettisoned his underwing load and stood on the brakes. Unhappily, the US Marines had just dug a new series of trenches across the overrun. It was fairly exciting - I was waiting for a take-off to the north at the invert where you see an aircraft turning on to the runway, idly watching a B57 squadron scramble into the south. Suddenly, all these iron bombs were bouncing across my nose, followed by the smoking B57.
My choice would be, when reduced power is used for take-off, is to use the methodology applicable to your type that allows full (rated?) power to be introduced if there is any doubt. Clearly, on types where Vmcg is an issue, that speed would need to be known.
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I understand the reasons behind why operators like to use reduced thrust on take-off - noise abatement, prolongs engine life etc.
My question is, does anyone know how significant the effect is? Especially with jet engines - would conducting every take-off at normal take-off power significantly reduce the engine time between overhauls? Or is it more a theoretical engineering idea that's just become ingrained into airline operating culture?
My question is, does anyone know how significant the effect is? Especially with jet engines - would conducting every take-off at normal take-off power significantly reduce the engine time between overhauls? Or is it more a theoretical engineering idea that's just become ingrained into airline operating culture?
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Haven't posted for a while but have just caught up on all the posts after a few days away. I'm no scientist but from what has been brought up in the technical posts......
The 744 had a gross weight calculation system as an option. This was years ago. We never used it, can't remember why. If Boeing built it back in the 80's, then a previous poster was probably right in assuming that the commercial departments of the world discounted the usefulness of such a system in favour of the lucrative "standard weights". Maybe it should be re-introduced. Just how much water are we carrying for those First Class showers.....?
Using a flex temp at a light weight or TOGA thrust at a heavy weight, in the same aeroplane, on the same runway, with the same environmental conditions, will result in you using roughly the same amount of runway. That's the whole premise behind using reduced thrust. You use all the runway and less thrust to get you to the required speed when you are light. If you are heavier, you need more thrust to get you to the required speed before you run out of tarmac. It follows that you should rotate near the same part of the runway regardless of your weight. This is great if you fly on and off that particular runway often. Not so great if you visit 100 destinations a year.
The trend vector shows on your air speed indicator, and is thus an indication of your rate of change of AIR speed (which is what you need to get airborne). The reactive windshear system uses airspeed fluctuations (among other inputs), that you see on the trend vector, to warn you when you get into a windshear situation. Before trend vectors previous posters used timed airspeed checks or distance to go markers (both of which gave you an idea of your rate of acceleration in airspeed). If you have a trend vector, you don't need a timed check or distance to go markers (although Bitchin' Betty the RAAS lady will calmly tell you that you have 1000 remaining). The trend vector is more or less instantaneous and is thus more accurate than a timed check, or gut feeling as you whiz past the distance to go markers.
If we have
We should have all we need to tell us whether out acceleration/energy is sufficient to get us airborne before the end of the runway. I know this is all stuff that we work out before we blast off, and that the speeds we come up with are supposed to cover us, but humour me and read on.....
The first three items in the list are aircraft system derived.
The remaining ones are what we punch into the FOVE/BLT.
If you can combine all these elements, (plus a few more, including Bitchin' Betty) would you not have a system that could tell you instantaneously (as the reactive windshear system does) that you have insufficient energy to get off that runway on that day?
It could activate when TO thrust was set (Flex, Assumed Temp, or TOGA) and give you the option of going TOGA straight away or discontinuing the takeoff.
This all makes perfect sense to me at the moment, but feel fee to fire away as I'm sure there is something I haven't considered that will see my brilliant idea shot down in flames!
The 744 had a gross weight calculation system as an option. This was years ago. We never used it, can't remember why. If Boeing built it back in the 80's, then a previous poster was probably right in assuming that the commercial departments of the world discounted the usefulness of such a system in favour of the lucrative "standard weights". Maybe it should be re-introduced. Just how much water are we carrying for those First Class showers.....?
Using a flex temp at a light weight or TOGA thrust at a heavy weight, in the same aeroplane, on the same runway, with the same environmental conditions, will result in you using roughly the same amount of runway. That's the whole premise behind using reduced thrust. You use all the runway and less thrust to get you to the required speed when you are light. If you are heavier, you need more thrust to get you to the required speed before you run out of tarmac. It follows that you should rotate near the same part of the runway regardless of your weight. This is great if you fly on and off that particular runway often. Not so great if you visit 100 destinations a year.
The trend vector shows on your air speed indicator, and is thus an indication of your rate of change of AIR speed (which is what you need to get airborne). The reactive windshear system uses airspeed fluctuations (among other inputs), that you see on the trend vector, to warn you when you get into a windshear situation. Before trend vectors previous posters used timed airspeed checks or distance to go markers (both of which gave you an idea of your rate of acceleration in airspeed). If you have a trend vector, you don't need a timed check or distance to go markers (although Bitchin' Betty the RAAS lady will calmly tell you that you have 1000 remaining). The trend vector is more or less instantaneous and is thus more accurate than a timed check, or gut feeling as you whiz past the distance to go markers.
If we have
- GPS
- Trend Vector
- Wind Vector
- Runway length
- Weight (an accurate one)
- Elevation
- Temperature
- Runway conditions
We should have all we need to tell us whether out acceleration/energy is sufficient to get us airborne before the end of the runway. I know this is all stuff that we work out before we blast off, and that the speeds we come up with are supposed to cover us, but humour me and read on.....
The first three items in the list are aircraft system derived.
The remaining ones are what we punch into the FOVE/BLT.
If you can combine all these elements, (plus a few more, including Bitchin' Betty) would you not have a system that could tell you instantaneously (as the reactive windshear system does) that you have insufficient energy to get off that runway on that day?
It could activate when TO thrust was set (Flex, Assumed Temp, or TOGA) and give you the option of going TOGA straight away or discontinuing the takeoff.
This all makes perfect sense to me at the moment, but feel fee to fire away as I'm sure there is something I haven't considered that will see my brilliant idea shot down in flames!
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Like Jack Schidt, I have been trying to not poke my retired nose in here, but I do believe I can offer a couple of points not yet fully explored.
The first is a bit of local knowledge. 16/34 is long, but a cow of a R/W. 16 slopes down 0.9%. The threshold area of 34 has a localised slope of about 1.15% before it rolls over and aligns itself with the 0.9% up-slope. This means that it requires a very deep flare to not slam it on, and that necessarily higher flare point at night is always very hard to pick. It’s almost like a crop duster’s strip. On the 727-200 I carried a min of +15 to have extra energy on hand for the flare, and with any wind around, at least +20. So an overweight landing was almost certain to be heavy unless the PF grew up at YMML.
The downhill T/O on 16 can be & has been neutralised by the wind shifts along it. I’ve raised dust myself once, to everyone’s surprise definitely including mine. We rolled into a quartering headwind, but down the other end the sock was showing a stiff tail wind. Acceleration was slow, then seemed to stop, but by that point there was no way we would have been able to stop in what distance remained. You should have heard me go on about V & Distance checks after that! A wooded hill sits in the NE corner of the field, and it (the A/p) is surrounded by deep river gullies, producing marked local wind variations. Swirling winds don't always show at the sock or the anemometers. I can recall two occasions when microbursts out of a clear sky put one 727 down out of site in a gully off 27, and another 727 was held low off 16, rattling a lot of tiles quite a few miles out on the extended centreline. They got away, but both times by dint of being US aircraft which have always philosophically allowed beyond-limit-power to be set, and the engine's reduced life accepted.
I was involved years back in an AFAP tech reassessment of Boeing's wet runway stopping distances, and after a lot of work we were able to prove they were grossly in error. Oz T/o charts are now realistic for Acc/Stop in the wet, but it taught me that what is put out by a manufacturer can be determined by the sales team as often as by the performance wizzes, and I didn’t blindly accept all numbers. I worked through every new endorsement’s charts to produce a summary of rules of thumb, one mid-range speed for every approach, fail, & landing configuration, with a kts variation per coarse weight adjustment. It was soon easy to be within +/- 1 kt of the actual chart, and 3 or 4 times caught a gross error.
Back in the early 60's down at East Sale I watched a USAF C-124 Globemaster heading home to Hawaii. Loaded to the gills and hoping to overfly Fiji, they aborted 6 (yup, six) times before finally raising dust at the far end and disappearing over the curvature of the earth (it seemed). That led me into deep discussions with two other USAF crews, and I have been a convert of their system ever since. Their achieved_speed_Vs_distance check was (& still is as far as I can find on-line) set so that zero wheel braking was used for the abort. Mind you, the tyres must have been jolly hot towards the end, but the check can easily provide a completely low stress abort speed. Speed x time is a coarser check, but 80 kts by 1,800’ was a good catch all. Still is by the sound of it. A friend who has more hours up down the back than I ever got up the front mentally prepares to adopt the crash position on any T/O if the nose isn’t starting to lift by 37 seconds, FWIW.
Personally I think that the most valuable comment in this series was that of Dairyground - what an eye-opener. We aren’t the only safety obsessed people, and it sounds as if the aviator sector may need to think more widely. What >is< ISO9000, and why don’t I know about it? Dairyground?
Thanks all for bringing me up to speed.
This report is going to be an interesting read.
The first is a bit of local knowledge. 16/34 is long, but a cow of a R/W. 16 slopes down 0.9%. The threshold area of 34 has a localised slope of about 1.15% before it rolls over and aligns itself with the 0.9% up-slope. This means that it requires a very deep flare to not slam it on, and that necessarily higher flare point at night is always very hard to pick. It’s almost like a crop duster’s strip. On the 727-200 I carried a min of +15 to have extra energy on hand for the flare, and with any wind around, at least +20. So an overweight landing was almost certain to be heavy unless the PF grew up at YMML.
The downhill T/O on 16 can be & has been neutralised by the wind shifts along it. I’ve raised dust myself once, to everyone’s surprise definitely including mine. We rolled into a quartering headwind, but down the other end the sock was showing a stiff tail wind. Acceleration was slow, then seemed to stop, but by that point there was no way we would have been able to stop in what distance remained. You should have heard me go on about V & Distance checks after that! A wooded hill sits in the NE corner of the field, and it (the A/p) is surrounded by deep river gullies, producing marked local wind variations. Swirling winds don't always show at the sock or the anemometers. I can recall two occasions when microbursts out of a clear sky put one 727 down out of site in a gully off 27, and another 727 was held low off 16, rattling a lot of tiles quite a few miles out on the extended centreline. They got away, but both times by dint of being US aircraft which have always philosophically allowed beyond-limit-power to be set, and the engine's reduced life accepted.
I was involved years back in an AFAP tech reassessment of Boeing's wet runway stopping distances, and after a lot of work we were able to prove they were grossly in error. Oz T/o charts are now realistic for Acc/Stop in the wet, but it taught me that what is put out by a manufacturer can be determined by the sales team as often as by the performance wizzes, and I didn’t blindly accept all numbers. I worked through every new endorsement’s charts to produce a summary of rules of thumb, one mid-range speed for every approach, fail, & landing configuration, with a kts variation per coarse weight adjustment. It was soon easy to be within +/- 1 kt of the actual chart, and 3 or 4 times caught a gross error.
Back in the early 60's down at East Sale I watched a USAF C-124 Globemaster heading home to Hawaii. Loaded to the gills and hoping to overfly Fiji, they aborted 6 (yup, six) times before finally raising dust at the far end and disappearing over the curvature of the earth (it seemed). That led me into deep discussions with two other USAF crews, and I have been a convert of their system ever since. Their achieved_speed_Vs_distance check was (& still is as far as I can find on-line) set so that zero wheel braking was used for the abort. Mind you, the tyres must have been jolly hot towards the end, but the check can easily provide a completely low stress abort speed. Speed x time is a coarser check, but 80 kts by 1,800’ was a good catch all. Still is by the sound of it. A friend who has more hours up down the back than I ever got up the front mentally prepares to adopt the crash position on any T/O if the nose isn’t starting to lift by 37 seconds, FWIW.
Personally I think that the most valuable comment in this series was that of Dairyground - what an eye-opener. We aren’t the only safety obsessed people, and it sounds as if the aviator sector may need to think more widely. What >is< ISO9000, and why don’t I know about it? Dairyground?
Thanks all for bringing me up to speed.
This report is going to be an interesting read.
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Oh actually its a bit better - still got to get the right weight in there though. And you'll be approaching v1 by the time it finishes its calculation! Think you're on the right track.
Anyway those of us on the big twin are not quite as exposed to these performance things (as long as they both keep turning) - maybe two engines is the answer!
Anyway those of us on the big twin are not quite as exposed to these performance things (as long as they both keep turning) - maybe two engines is the answer!
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jack schidt wrote:
So what happened to "I wait for the report"?
I have written several statements and cancelled/deleted them. I wait for the report , but if the guys in the 2 front seats used 100T too little in the comp then good luck in your future jobs but dont make it a career in aviation!!!...
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mig3
You asked:
"would conducting every take-off at normal take-off power significantly reduce the engine time between overhauls? Or is it more a theoretical engineering idea that's just become ingrained into airline operating culture?"
No it's not theoretical. Some airlines track the life history of individual engines, so they know how they've been treated and their cost.
But the great experts are the engine manufacturers. Every customer demands a maintenance cost guarantee. The numbers they are quoted depend on, amongst other things, the average derate used. No good using what you call "normal power" and claiming on the maint cost g'tee. It won't wash.
"would conducting every take-off at normal take-off power significantly reduce the engine time between overhauls? Or is it more a theoretical engineering idea that's just become ingrained into airline operating culture?"
No it's not theoretical. Some airlines track the life history of individual engines, so they know how they've been treated and their cost.
But the great experts are the engine manufacturers. Every customer demands a maintenance cost guarantee. The numbers they are quoted depend on, amongst other things, the average derate used. No good using what you call "normal power" and claiming on the maint cost g'tee. It won't wash.
Last edited by Dysag; 29th Mar 2009 at 11:01.
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Although time to v1 looks suitable, it is not!!
It would be if there was a thrust problem. For a weight problem however, you are calculating time to a WRONG v1, with a WRONG thrust. On a short runway, I will not have any indication that I can still stop the aircraft after the WRONG time to the WRONG v1 if I suddenly weigh x tons MORE...
So it is the old saying... BS in, BS out.. and that goes for time to v1 as well...
It would be if there was a thrust problem. For a weight problem however, you are calculating time to a WRONG v1, with a WRONG thrust. On a short runway, I will not have any indication that I can still stop the aircraft after the WRONG time to the WRONG v1 if I suddenly weigh x tons MORE...
So it is the old saying... BS in, BS out.. and that goes for time to v1 as well...
(Making numbers up) If your V1 is 120 kt and you need 1000m to stop from V1, if you haven't reached 120kt by the calculated time you know:
- you are slower than 120kt and
- you have more than 1000m to stop.
The wrong time and wrong v1 only cause a problem if the extra weight has more effect on braking distance than it does on acceleration distance. This is possible, but it doesn't sound likely to me.
Time to V1 catches the error where your weight is too high and the thrust is too low - and the errors accumulate to provide extra margin.
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V1 is not the whole story. You also need to reach Vr before running out of runway.
If the weight is more than calculated, Vr is higher and acceleration is slower. The computer may sense the slower acceleration, and ask for more thrust, but it should also account for a higher Vr i.e ask for even more thrust.
Might be possible to do in real time but I'm not convinced yet.
If the weight is more than calculated, Vr is higher and acceleration is slower. The computer may sense the slower acceleration, and ask for more thrust, but it should also account for a higher Vr i.e ask for even more thrust.
Might be possible to do in real time but I'm not convinced yet.
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It sounds like the answer is not so much the time to V1 or any other speed, but what is your speed after the calculated time? If it's way below V1 you have a problem but also, by definition you have enough tarmac left in which to stop because you're stopping from a slower speed.
Isn't the right solution therefore to calculate how long it should take to get to V1 - if your speed is below V1 after x seconds then reject the takeoff?
Isn't the right solution therefore to calculate how long it should take to get to V1 - if your speed is below V1 after x seconds then reject the takeoff?