Balance Field Length
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Balance Field Length
I have read the recent previous post on this topic with great interest as most of my operations are out of aerodromes where takeoff weights are less than structural limit.By reducing MTOW for ambient conditions,are we creating a BFL?Does BFL calculation stop at 35ft therefore this TOW reduction considers obstacle clearance to 1500ft AGL?Most importantly would a decision either way at V1 at this weight give me a 
BFL scenario?
react personal eh what performance?
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J_T, Mutt,
I think that the scariest in recent history was the gentleman believing that V1 was an arbitrary figure derived from the WAT limit.
yawskidball, a BFL condition will exist entirely dependant upon the type of AFM data that you're using. Most use it, some don't, some use Clearway and/or unequal Stopway, some don't. I prefer to work with unbalanced data (basically because I'm a very unbalanced person), it gives greater flexibility, particularly when factors affecting Accelerate-Stop, but not affecting Accelerate-Go (such as Anti-Skid being Inop) exist. One then flies at the most limiting of the 2 conditions.
If obstacles have forced you to optimise the Obstacle Climb Limit against the Field length used, thus reducing the Effective Operational Length (EOL), and you're using Balanced Field data from the AFM, then the operation is still BFL, even though you're not availing yourself of the full runway length.
Obstacle clearance is considered to 1500 feet, or GREATER, if required to satisfy obstacles (That's a very short version of the total picture).
Regards,
Old Smokey (Taking holidays now to enable sensible discourse to resume on PPruNe)
.
I think that the scariest in recent history was the gentleman believing that V1 was an arbitrary figure derived from the WAT limit.
yawskidball, a BFL condition will exist entirely dependant upon the type of AFM data that you're using. Most use it, some don't, some use Clearway and/or unequal Stopway, some don't. I prefer to work with unbalanced data (basically because I'm a very unbalanced person), it gives greater flexibility, particularly when factors affecting Accelerate-Stop, but not affecting Accelerate-Go (such as Anti-Skid being Inop) exist. One then flies at the most limiting of the 2 conditions.
If obstacles have forced you to optimise the Obstacle Climb Limit against the Field length used, thus reducing the Effective Operational Length (EOL), and you're using Balanced Field data from the AFM, then the operation is still BFL, even though you're not availing yourself of the full runway length.
Obstacle clearance is considered to 1500 feet, or GREATER, if required to satisfy obstacles (That's a very short version of the total picture).
Regards,
Old Smokey (Taking holidays now to enable sensible discourse to resume on PPruNe)
.
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Old Smokey dont go too far I find your posts provide and wisdom and joy.
john_t and I must get our best NAAFI china cups out and intitiate you into our port tasting circle
, 'twould make for a fascinating evening. 
john_t and I must get our best NAAFI china cups out and intitiate you into our port tasting circle
, 'twould make for a fascinating evening.
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Originally Posted by Old Smokey
J_T, Mutt,
I think that the scariest in recent history was the gentleman believing that V1 was an arbitrary figure derived from the WAT limit.
yawskidball, a BFL condition will exist entirely dependant upon the type of AFM data that you're using. Most use it, some don't, some use Clearway and/or unequal Stopway, some don't. I prefer to work with unbalanced data (basically because I'm a very unbalanced person), it gives greater flexibility, particularly when factors affecting Accelerate-Stop, but not affecting Accelerate-Go (such as Anti-Skid being Inop) exist. One then flies at the most limiting of the 2 conditions.
If obstacles have forced you to optimise the Obstacle Climb Limit against the Field length used, thus reducing the Effective Operational Length (EOL), and you're using Balanced Field data from the AFM, then the operation is still BFL, even though you're not availing yourself of the full runway length.
Obstacle clearance is considered to 1500 feet, or GREATER, if required to satisfy obstacles (That's a very short version of the total picture).
Regards,
Old Smokey (Taking holidays now to enable sensible discourse to resume on PPruNe)
.
I think that the scariest in recent history was the gentleman believing that V1 was an arbitrary figure derived from the WAT limit.
yawskidball, a BFL condition will exist entirely dependant upon the type of AFM data that you're using. Most use it, some don't, some use Clearway and/or unequal Stopway, some don't. I prefer to work with unbalanced data (basically because I'm a very unbalanced person), it gives greater flexibility, particularly when factors affecting Accelerate-Stop, but not affecting Accelerate-Go (such as Anti-Skid being Inop) exist. One then flies at the most limiting of the 2 conditions.
If obstacles have forced you to optimise the Obstacle Climb Limit against the Field length used, thus reducing the Effective Operational Length (EOL), and you're using Balanced Field data from the AFM, then the operation is still BFL, even though you're not availing yourself of the full runway length.
Obstacle clearance is considered to 1500 feet, or GREATER, if required to satisfy obstacles (That's a very short version of the total picture).
Regards,
Old Smokey (Taking holidays now to enable sensible discourse to resume on PPruNe)
.
But I doubt WAT limit can be enough to determine V1...
After all, what I see of the definitions...
A "balanced field" seems to make no sense except for airplanes that have more than one engine and can safely climb with one of engines inoperative, but no other failures.
The balanced field means that:
- an aircraft accelerates with all engines functional
- at a certain point, 1 engine out of 2 goes out - but no other failures occur
- 2 seconds later the aircraft shuts down the good engine, but does not apply reverse thrust
- and then the aircraft stops precisely at the end of the balanced field
- ass-uming that the wind throughout the accelerate-stop sequence is precisely unchanging
- ass-uming an ass-umed total mass of the craft, including payload (not the real, physical weight! loaded planes are NOT weighed!, cannot be done at a gate subject to wind)
and the BFL is then the shortest field length where the aircraft also could unstick, reach certain arbitrary height (15 feet?) before the end of runway and continue to climb at a certain rather arbitrary speed (V2) and quite arbitrary gradient (2,4 %, 2,7 %, 3,0 %, ...)
Surely there are plenty of other details, but it seems that you are already riddled with rather arbitrary ass-umptions, some of which are enacted by law, though.
So, V1 is already arbitrary on the, itself arbitrary, balanced field. Now think of a field longer than arbitrary...
Depending on the OEI thrust and WAT, several planes are known to be able to take off with OEI from the start of roll. Does it mean V1 equals zero, or negative for the matter?
And on the other hand, with a short take-off/landing plane on a long runway, it seems possible to get airborne in a short stretch of runway, hop to 35 or 15 or something feet and proceed to land on the rest of the same runway. Does it mean V1>>V2?
I understand that the stopping distance is relatively well physically constrained for a given real groundspeed of plane, real unchanging braking conditions and real unchanging functionality of the brakes. With, say, 4000 feet of runway left, the V1 might make a difference between coming to a halt 100 feet short of the runway end or tipping over to a ravine 100 feet beyond.
But obviously, it makes all the difference where you are at "V1": whether it actually is 3000 feet left, or 5000 feet...
Oh, and another example. Suppose headwinds increase at some point in takeoff. Does it mean that you are suddenly beyond V1? But you still have a lot of runway ahead, and your Accelerate-Stop chances are actually slightly improved (more wind drag). And the opposite - headwind decreasing or tailwind gusting, stops you from reaching V1 as the airspeed does not increase as planned, AND Accelerate-Go gets much harder - yet Accelerate-Stop is not getting any easier, and delaying abort would surely mean disastrous overrun...
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Woomera West
... indeed, good sir ... nothing quite as fine as a good port from a coffee cup in the cantina to protect the guilty from accusations of inappropriate consumption of spirituous and fermented beverages.
Old Smokey and I last spoke about 25-30 years ago before he got into the flying side of the game .. he recalls me quite clearly but I cannot put a face to the memory (clearly my Alzheimers is more advanced than is his ..) .. so far we haven't been able to catch up for a convivial. I have no doubt that a three-way port session would be a delightful way to have three fine chaps converse on matters technical, hysterical, and nautical.
chornedsnorkack
I'm sure there is something subtle in your handle although my lack of imagination causes it to remain elusive in the recesses of my tiny brain ..
V1 most certainly is NOT arbitrary (although one could/can schedule an acceptable V1 range for the day if one so wished and data were available).
WAT has naught to do with it as WAT relates solely to minimum climb performance standards as prescribed in the relevant aircraft Design Standard.
BFL generally and largely is irrelevant as it is only a convenience construct and has no great significance in its own right .. in the same vein as the datum position for weight and balance calculations ...
What you are saying is fine and can be summarised very simply .. certification performance data is artificial in that it establishes lines in the sand for very well defined boundary test conditions. If the line pilot wants to reproduce the data, he needs to have the same boundary conditions and that prerequisite, generally, is unachieveable. It follows that the line pilot probably is going to be able to go close (to a greater or lesser extent) but not quite get to the mark .. and, if achieving the mark is important (rocks at the end of the runway ?), then maybe that difficulty needs to be factored into the operational decision making equation along the way somewhere ... ?
... indeed, good sir ... nothing quite as fine as a good port from a coffee cup in the cantina to protect the guilty from accusations of inappropriate consumption of spirituous and fermented beverages.
Old Smokey and I last spoke about 25-30 years ago before he got into the flying side of the game .. he recalls me quite clearly but I cannot put a face to the memory (clearly my Alzheimers is more advanced than is his ..) .. so far we haven't been able to catch up for a convivial. I have no doubt that a three-way port session would be a delightful way to have three fine chaps converse on matters technical, hysterical, and nautical.
chornedsnorkack
I'm sure there is something subtle in your handle although my lack of imagination causes it to remain elusive in the recesses of my tiny brain ..
V1 most certainly is NOT arbitrary (although one could/can schedule an acceptable V1 range for the day if one so wished and data were available).
WAT has naught to do with it as WAT relates solely to minimum climb performance standards as prescribed in the relevant aircraft Design Standard.
BFL generally and largely is irrelevant as it is only a convenience construct and has no great significance in its own right .. in the same vein as the datum position for weight and balance calculations ...
What you are saying is fine and can be summarised very simply .. certification performance data is artificial in that it establishes lines in the sand for very well defined boundary test conditions. If the line pilot wants to reproduce the data, he needs to have the same boundary conditions and that prerequisite, generally, is unachieveable. It follows that the line pilot probably is going to be able to go close (to a greater or lesser extent) but not quite get to the mark .. and, if achieving the mark is important (rocks at the end of the runway ?), then maybe that difficulty needs to be factored into the operational decision making equation along the way somewhere ... ?
Last edited by john_tullamarine; 1st Feb 2006 at 21:06.
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Originally Posted by john_tullamarine
chornedsnorkack
I'm sure there is something subtle in your handle although my lack of imagination causes it to remain elusive in the recesses of my tiny brain ..
I'm sure there is something subtle in your handle although my lack of imagination causes it to remain elusive in the recesses of my tiny brain ..
Originally Posted by john_tullamarine
V1 most certainly is NOT arbitrary (although one could/can schedule an acceptable V1 range for the day if one so wished and data were available).
WAT has naught to do with it as WAT relates solely to minimum climb performance standards as prescribed in the relevant aircraft Design Standard.
WAT has naught to do with it as WAT relates solely to minimum climb performance standards as prescribed in the relevant aircraft Design Standard.
Originally Posted by john_tullamarine
What you are saying is fine and can be summarised very simply .. certification performance data is artificial in that it establishes lines in the sand for very well defined boundary test conditions. If the line pilot wants to reproduce the data, he needs to have the same boundary conditions and that prerequisite, generally, is unachieveable. It follows that the line pilot probably is going to be able to go close (to a greater or lesser extent) but not quite get to the mark .. and, if achieving the mark is important (rocks at the end of the runway ?), then maybe that difficulty needs to be factored into the operational decision making equation along the way somewhere ... ?
It is not true that the interior of the Flight Envelope is all white and safe. There is plenty of gray everywhere, and there are corners which actually are rather dark gray. On the other hand, many of the lines are drawn right across rather light gray.
So, a line pilot must first be aware of where exactly the black and dark grey exist. Second, the pilot must not assume that the interior of the envelope is white throughout, or that it is uniformly light grey. Third, the pilot should be aware of the lines across light gray.
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A reference to Harry Potter series.
ah ... that would explain why it meant naught to me ..
Surely the climb performance and Weight, Altitude, Temperature are vitally important to V1 choice?
Unrelated.
Climb to screen will depend on weight etc., and that is wrapped up in the TOD calculations.
WAT limits are certification Design Standard lines in the sand to limit maximum weights to values at which the aircraft can demonstrate a modest OEI climb gradient capability in the various segments .. nothing to do with runway considerations.
V1 looks at handling (Vmcg, Vmu), ASD (higher V1), TOR (lower V1), and TOD (lower V1).
This highlights the need for the takeoff calculation to go through all the various limiting calculations to determine which is the most limiting and that limit then determines the RTOW on the day.
As an anecdotal tale to illustrate this need .. I was involved in an audit on an operator some years ago and, sitting in a little terminal in the middle of nowhere waiting for a flight from A to B, I idly did some back-of-a-fag-packet calculations to compare their RTOW tables to the AFM charts. It rapidly became apparent that they had based all their calculations (for a runway which was particularly critical for the company paying for the audit) on ASD limits. Unfortunately, TOD1 was the limiting animal and they were operating significantly above the limiting RTOW day in day out. The client rapidly suggested that I take off my auditor hat and put on my ops engineer version and fix the problem pronto .. which we could do only to a limited extent. Of interest, some years later, I had to train a number of pilots from that operator onto the 737 and the management folk recognised me straight away from the previous encounter ... appears I had acquired a bit of a cult respect within the flight operations group for picking up the error (which was, in fact, quite obvious after a few minutes work while sitting in the aforementioned terminal).
the certified Flight Envelope is an envelope of sharp lines and corners drawn across a picture of shades of gray
The man wins the $64 ... you got it in one ... where the sharpness relates to an idealised world ... and the greys relate to the real world.
ah ... that would explain why it meant naught to me ..
Surely the climb performance and Weight, Altitude, Temperature are vitally important to V1 choice?
Unrelated.
Climb to screen will depend on weight etc., and that is wrapped up in the TOD calculations.
WAT limits are certification Design Standard lines in the sand to limit maximum weights to values at which the aircraft can demonstrate a modest OEI climb gradient capability in the various segments .. nothing to do with runway considerations.
V1 looks at handling (Vmcg, Vmu), ASD (higher V1), TOR (lower V1), and TOD (lower V1).
This highlights the need for the takeoff calculation to go through all the various limiting calculations to determine which is the most limiting and that limit then determines the RTOW on the day.
As an anecdotal tale to illustrate this need .. I was involved in an audit on an operator some years ago and, sitting in a little terminal in the middle of nowhere waiting for a flight from A to B, I idly did some back-of-a-fag-packet calculations to compare their RTOW tables to the AFM charts. It rapidly became apparent that they had based all their calculations (for a runway which was particularly critical for the company paying for the audit) on ASD limits. Unfortunately, TOD1 was the limiting animal and they were operating significantly above the limiting RTOW day in day out. The client rapidly suggested that I take off my auditor hat and put on my ops engineer version and fix the problem pronto .. which we could do only to a limited extent. Of interest, some years later, I had to train a number of pilots from that operator onto the 737 and the management folk recognised me straight away from the previous encounter ... appears I had acquired a bit of a cult respect within the flight operations group for picking up the error (which was, in fact, quite obvious after a few minutes work while sitting in the aforementioned terminal).
the certified Flight Envelope is an envelope of sharp lines and corners drawn across a picture of shades of gray
The man wins the $64 ... you got it in one ... where the sharpness relates to an idealised world ... and the greys relate to the real world.
