B777 300ER Fuel Burn
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The fact is that every aircraft is designed to have a sweet spot and the B747-400 does not like getting slow. The difference in fuel burn between M.86 and M.85 is minimal but remember...
TIME IS MONEY.
TIME IS MONEY.
I recall some years ago a 'new' Captain on the L1011 was showing me how he was 'saving' fuel by cruising at M.82 instead of M.85....the latter requested by the company.
Dense as a brick wall, comes to mind.
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Yes, a good point made there!
Why do so many line pilots believe they know better than the Flight Department?
Do they believe the Flight Department is staffed by turkeys?...or are they just full of themselves?
Having flown with a variety of airlines over the years the Ops Manuals presented to me have always been satisfactory, so why would I challenge them?
Why do so many line pilots believe they know better than the Flight Department?
Do they believe the Flight Department is staffed by turkeys?...or are they just full of themselves?
Having flown with a variety of airlines over the years the Ops Manuals presented to me have always been satisfactory, so why would I challenge them?
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Well said, amos2
I've worked with many pilots and bean counters over the years.
Whilst it's true that most bean counters couldn't be professional pilots, it's also true that very few pilots would make good analysts, performance engineers or economists.
Every pilot accumulates his own set of "rules of thumb", and some will defend them to the end, right or wrong. One common rule is that the bean counters are always incompetent.
Whilst it's true that most bean counters couldn't be professional pilots, it's also true that very few pilots would make good analysts, performance engineers or economists.
Every pilot accumulates his own set of "rules of thumb", and some will defend them to the end, right or wrong. One common rule is that the bean counters are always incompetent.
Last edited by Dysag; 27th May 2008 at 12:47.
A comparable approach was used in the UK bus industry for many years, where cost per mile was the golden index. This was an easy one to bean count in pre-computer days, just add up all the costs, divide by the number of miles driven. It was used for all sorts of decision making such as whether a route was "profitable" (ie whether revenue exceeded the cost for the miles driven). It also accounted for so many small bus garages around towns and cities, to minimise the miles driven to start the service.
I used to call this "Economics of the Lower 6th form class", and in the end others agreed. The actual cost varies widely for different types of miles driven, and the global figure should never have be used for detailed operational decisions. Not surprisingly, calculating cost per hour, a concept I took from aviation, gave notably different figures, but there were too many variables for those accustomed to an easy life with an easy cost index they were familiar with. It was all very similar to the discussion above.
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I don't agree that CI is effectively irrelevant and we might as well fly at 0.84M. Yes, we might land sooner, having used pretty much the same fuel, but the extra wear n the engine is NOT negligible (excuse the double neagtive). Anyone with any knowledge of the hot end problems appearing on the GE 90-115 will appreciate that. Just talk to the engineers.
Frequently, LRC is faster (and close to M0.84) that the prevailing low CI's, with a minute or two flight time advantage, but any attempt to reduce hot end fatigue is a good one. Reduced thrust take-offs are an example - even on the RR engines we were told (quite a while ago now) that 1°C reduction in assumed temp lowered the turbine temp by 30°C. Factor in a few degrees C over 9 hours and that's a lot of fatigue.
Gillegan -correct about the UPS program -why we can't just be given a time/speed/altitude at a given waypoint on the STAR and run from there I'll never understand. UPS are trialling, or about to start this sort of thing, using tight RNP numbers, in the middle of the night when they are the only ones around.
Frequently, LRC is faster (and close to M0.84) that the prevailing low CI's, with a minute or two flight time advantage, but any attempt to reduce hot end fatigue is a good one. Reduced thrust take-offs are an example - even on the RR engines we were told (quite a while ago now) that 1°C reduction in assumed temp lowered the turbine temp by 30°C. Factor in a few degrees C over 9 hours and that's a lot of fatigue.
Gillegan -correct about the UPS program -why we can't just be given a time/speed/altitude at a given waypoint on the STAR and run from there I'll never understand. UPS are trialling, or about to start this sort of thing, using tight RNP numbers, in the middle of the night when they are the only ones around.
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Irrelevant indeed
Trimotor wrote:
"I don't agree that CI is effectively irrelevant and we might as well fly at 0.84M. Yes, we might land sooner, having used pretty much the same fuel, but the extra wear n the engine is NOT negligible (excuse the double neagtive). Anyone with any knowledge of the hot end problems appearing on the GE 90-115 will appreciate that. Just talk to the engineers."
I'm talking about facts, not guessing. You can take it for granted from a Mechanical Engineer with PG on Aircraft Design graduate: you land 6-7 min earlier on a 7 hours sector, burn the same amount of fuel, and yes, engine wear is negligible. Do it yourself: establish on a typical FL and weight at M.83,take note of every single engine parameter, accelerate to M.84, wait for stabilization (not less than 5 min) and take the same notes. Compare. You wont notice a difference.
Assumed temp takeoffs is a completely different thing, and of course, impact on engine life is definitive.
Sometimes I think this bean counters and so called "engineering or perfomance analysis" departments are prone in going on some nit picking issues completely displaced from the real life only to justify their existence on the payroll...they would be much more useful with more involvement with the hands on people, the pilots.
"I don't agree that CI is effectively irrelevant and we might as well fly at 0.84M. Yes, we might land sooner, having used pretty much the same fuel, but the extra wear n the engine is NOT negligible (excuse the double neagtive). Anyone with any knowledge of the hot end problems appearing on the GE 90-115 will appreciate that. Just talk to the engineers."
I'm talking about facts, not guessing. You can take it for granted from a Mechanical Engineer with PG on Aircraft Design graduate: you land 6-7 min earlier on a 7 hours sector, burn the same amount of fuel, and yes, engine wear is negligible. Do it yourself: establish on a typical FL and weight at M.83,take note of every single engine parameter, accelerate to M.84, wait for stabilization (not less than 5 min) and take the same notes. Compare. You wont notice a difference.
Assumed temp takeoffs is a completely different thing, and of course, impact on engine life is definitive.
Sometimes I think this bean counters and so called "engineering or perfomance analysis" departments are prone in going on some nit picking issues completely displaced from the real life only to justify their existence on the payroll...they would be much more useful with more involvement with the hands on people, the pilots.
Last edited by fullforward; 29th May 2008 at 15:34.
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Silly question
The consensus seems to be that flying a little slower will not result in additional fuel costs. The corollary is that there is a range of speeds where the fuel cost remains pretty much constant. There seem to be arguments coming down both ways on whether there is any maintenance penalty either way.
Could it be that the beancounters are thinking that if aircraft are scheduled to fly at the slow end of this roughly equal cost range, effects of attempts to mitigate delays (i.e. trying to make up time in the air) would be less costly?
After reading all the opinions each way, this seemed to me to be a possibility.
I'm not sure if it makes practical sense, but I've seen things like this come out of numerical analysis before.
Could it be that the beancounters are thinking that if aircraft are scheduled to fly at the slow end of this roughly equal cost range, effects of attempts to mitigate delays (i.e. trying to make up time in the air) would be less costly?
After reading all the opinions each way, this seemed to me to be a possibility.
I'm not sure if it makes practical sense, but I've seen things like this come out of numerical analysis before.
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Someone wrote above 'Dont you need two planes on the same route at same time'. Actually you would need enough planes (50??) on the same route in the same conditions to have resutls that were statistically significant. The more different the results, the less planes that would be needed. In reality that is not realistic, so a lot of data from 1000s of trips could be merged and smoothed to give statistically significant results. It requires a bit of math, but is legitimate.
Now, before anyone says I am not correct, this is OVER simplified for laymen, and gives a feel for how it is done, but it is a lot more complex.
And... in reality, a good statistician can make statisitics say anything!!
TME
Now, before anyone says I am not correct, this is OVER simplified for laymen, and gives a feel for how it is done, but it is a lot more complex.
And... in reality, a good statistician can make statisitics say anything!!
TME
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My airline has solved the fuel problem by removing the winglets and mach meter.
We now turn left at the control tower and taxi to our destination.
Fuel burn per hour is minimal but flying hours have gone through the roof.
We now turn left at the control tower and taxi to our destination.Fuel burn per hour is minimal but flying hours have gone through the roof.
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All very good points on the fuel burn, nice idea's about working with the different companies to improve performance.
BUT the bottom line, the golden rule, they pay the gold - we follow the rules, I follow SOP.
Plus, I get paid by the minute, why fly faster than flight plan? It just makes more noise in the cockpit of the old 747 200's.
WD
BUT the bottom line, the golden rule, they pay the gold - we follow the rules, I follow SOP.
Plus, I get paid by the minute, why fly faster than flight plan? It just makes more noise in the cockpit of the old 747 200's.
WD
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OK
Whale,
Nobody is advocating here undiscipline or creating own rules.
The fact is, under difficult times like we are experiencing, a good partnership between pilots and operations/engineering management is highly beneficial. I guess is a little shortsighted to only enjoy the possible personal advantages in flying slow or fast...
Experience and knowledge could led to some more creative techniques than to simply blind following the sops or whatever. Nowadays, pilots should be a little more than trained dogs...
Nobody is advocating here undiscipline or creating own rules.
The fact is, under difficult times like we are experiencing, a good partnership between pilots and operations/engineering management is highly beneficial. I guess is a little shortsighted to only enjoy the possible personal advantages in flying slow or fast...
Experience and knowledge could led to some more creative techniques than to simply blind following the sops or whatever. Nowadays, pilots should be a little more than trained dogs...
Last edited by fullforward; 31st May 2008 at 18:14.
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You are right of course, but it should also remind us of the fact that statistics are like miniskirts: they show us everything but they hide the essential...
Sorry...
Sorry...
