1st/2nd Segment Obstacle Correction Factor
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1st/2nd Segment Obstacle Correction Factor
To the performance gurus. I'd like some help in QAing the following procedure:
Our ops manual has a procedure to correct the published TODA/STODA to guarantee that both 1st and 2nd Segments are able to be conducted clear of obstacles. This is due to the reasoning that when using ERSA STODAs, the height and horizontal distance for the limiting obstacle(s) is unknown and the first stage may be compromised.
The fix is to reduce the STODA by a given margin, thereby supposedly containing the 1st stage within the runway strip e.g. If using a 5% STODA, 60m is subtracted, reducing down to a 1.6% STODA correction of 20m. This then gives a corrected TODA, which is used for calculating runway and climb limitations.
Issues:
1. If operating at a non-obstacle limited airfield, the corrected TODA could be longer than the actual true TORA e.g. subtracting 20m on a 1.6% slope would still put the TODA in the clearway (We only calculate a balanced field V1)
Fix: Need to use the lessor of ASDA, TORA or corrected TODA.
2. If they're worried about 1st stage protection, then 60m (197ft) seems a bit small. A max V2 of 150kts (253fps) means that the "buffer" is gone in less than a second, and the aircraft will not be climbing at the 2nd stage gradient when it starts to impinge outside the clearway.
Fix: Better gear retraction time (therefore distance) data?
We don't use this often as most of our ops are covered by RTOW charts.
Does anyone else use a similar procedure, or do you simply accept the fact that the first stage does not actually impose upon published gradients, and only consider 2nd stage performance (or use what ever the ops section gives you?)?
Anyone like to add constructive criticism?
Our ops manual has a procedure to correct the published TODA/STODA to guarantee that both 1st and 2nd Segments are able to be conducted clear of obstacles. This is due to the reasoning that when using ERSA STODAs, the height and horizontal distance for the limiting obstacle(s) is unknown and the first stage may be compromised.
The fix is to reduce the STODA by a given margin, thereby supposedly containing the 1st stage within the runway strip e.g. If using a 5% STODA, 60m is subtracted, reducing down to a 1.6% STODA correction of 20m. This then gives a corrected TODA, which is used for calculating runway and climb limitations.
Issues:
1. If operating at a non-obstacle limited airfield, the corrected TODA could be longer than the actual true TORA e.g. subtracting 20m on a 1.6% slope would still put the TODA in the clearway (We only calculate a balanced field V1)
Fix: Need to use the lessor of ASDA, TORA or corrected TODA.
2. If they're worried about 1st stage protection, then 60m (197ft) seems a bit small. A max V2 of 150kts (253fps) means that the "buffer" is gone in less than a second, and the aircraft will not be climbing at the 2nd stage gradient when it starts to impinge outside the clearway.
Fix: Better gear retraction time (therefore distance) data?
We don't use this often as most of our ops are covered by RTOW charts.
Does anyone else use a similar procedure, or do you simply accept the fact that the first stage does not actually impose upon published gradients, and only consider 2nd stage performance (or use what ever the ops section gives you?)?
Anyone like to add constructive criticism?
Last edited by Ex Douglas Driver; 2nd May 2006 at 01:36. Reason: Edits in Itallics to correct errors
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Ex Douglas Driver,
Unless your aircraft has a very benign first segment performance, your post frightens the living daylights out of me ... sadly it reflects the generally abysmal level of performance knowledge amongst many of the piloting fraternity. It is unfortunate that the Australian fraternity doesn't have to wade through the likes of Perf A as the traditional CASA (and precedent organisations) performance exams (and the related Industry training courses) tend to gloss over the nitty gritty of getting off and away from the bumpy bits. One needs to keep in mind that the first segment may well be the critical takeoff consideration .. albeit that a lot of folk ignore it to a greater or lesser extent.
(a) having done a LOT of work in the past on precisely the same problem with some quite limiting first segment aircraft, I suggest that the 60m/20m possibly are figures plucked out of thin air .. are you able to provide a bit more meat as to the rationale and engineering logic ? Certainly those sort of numbers make no sense when viewed against the geometric constructions I've done in the past ...
(b) a bit risky to mix TORA and TODA/STODA .. bit like apples and oranges.
(c) if you elect to make an artificial "TORA" exceeding the runway declared TORA, who authorises such a practice ? Not sure that I would like to be on the receiving end of that one from a skilled barrister in court after the accident ...
The simplest way to achieve your goal is one of the following ..
(a) make the weight such that the first segment fits in the available TOD. Generally, this is only suitable for one-off get-me-home-quick exercises as it is usually very conservative.
(b) make the weight such that the available first segment gradient is not less than the required obstacle clear surface gradient. Likewise very conservative.
(c) do the obstacle analysis .. quite easy, really .. it certainly is not correct to say that the obstacle data is unknown .. but you might have to do a bit of legwork to track it down ... options -
(i) get the obstacle data .. approach the airport owners and/or the surveyor who did the survey .. often free if one asks nicely but might cost a few dollars or a couple of beers .... or
(ii) work a reverse engineering analysis to figure the STODA/TODA intersections from the RDS data. This will not be entirely accurate with regard to the obstacles due to round off in the ERSA data but will be a bit conservative so all's well. In general, the calculated data is reasonably close to the actual critical obstacles which formed the basis for the RDS figures .. I don't think anyone has done a simple inclino survey for many years, if ever ? Certainly, playing with AFMs over the past thirty odd years as a consulting engineer, I haven't come across one .. always been a discrete survey.
(iii) with the obstacle set (either real or inferred) it is a simple geometric exercise to fit the AFM data to the obstacle profiles
Presuming that you fly for a local operator, you might consider suggesting that an appropriate person in the organisation seek professional guidance on the matter .. in the first instance, I guess that Old Smokey or I would be happy to have a quick look at the engineering philosophy as we are both very familiar with the Oz operating and regulatory environment.
Two other thoughts ..
(a) don't forget that the runway slope might just catch up with and smite the aircraft for WAT conditions ..
(b) what does your company do about the third segment acceleration in this general T/O analysis case ?
Unless your aircraft has a very benign first segment performance, your post frightens the living daylights out of me ... sadly it reflects the generally abysmal level of performance knowledge amongst many of the piloting fraternity. It is unfortunate that the Australian fraternity doesn't have to wade through the likes of Perf A as the traditional CASA (and precedent organisations) performance exams (and the related Industry training courses) tend to gloss over the nitty gritty of getting off and away from the bumpy bits. One needs to keep in mind that the first segment may well be the critical takeoff consideration .. albeit that a lot of folk ignore it to a greater or lesser extent.
(a) having done a LOT of work in the past on precisely the same problem with some quite limiting first segment aircraft, I suggest that the 60m/20m possibly are figures plucked out of thin air .. are you able to provide a bit more meat as to the rationale and engineering logic ? Certainly those sort of numbers make no sense when viewed against the geometric constructions I've done in the past ...
(b) a bit risky to mix TORA and TODA/STODA .. bit like apples and oranges.
(c) if you elect to make an artificial "TORA" exceeding the runway declared TORA, who authorises such a practice ? Not sure that I would like to be on the receiving end of that one from a skilled barrister in court after the accident ...
The simplest way to achieve your goal is one of the following ..
(a) make the weight such that the first segment fits in the available TOD. Generally, this is only suitable for one-off get-me-home-quick exercises as it is usually very conservative.
(b) make the weight such that the available first segment gradient is not less than the required obstacle clear surface gradient. Likewise very conservative.
(c) do the obstacle analysis .. quite easy, really .. it certainly is not correct to say that the obstacle data is unknown .. but you might have to do a bit of legwork to track it down ... options -
(i) get the obstacle data .. approach the airport owners and/or the surveyor who did the survey .. often free if one asks nicely but might cost a few dollars or a couple of beers .... or
(ii) work a reverse engineering analysis to figure the STODA/TODA intersections from the RDS data. This will not be entirely accurate with regard to the obstacles due to round off in the ERSA data but will be a bit conservative so all's well. In general, the calculated data is reasonably close to the actual critical obstacles which formed the basis for the RDS figures .. I don't think anyone has done a simple inclino survey for many years, if ever ? Certainly, playing with AFMs over the past thirty odd years as a consulting engineer, I haven't come across one .. always been a discrete survey.
(iii) with the obstacle set (either real or inferred) it is a simple geometric exercise to fit the AFM data to the obstacle profiles
Presuming that you fly for a local operator, you might consider suggesting that an appropriate person in the organisation seek professional guidance on the matter .. in the first instance, I guess that Old Smokey or I would be happy to have a quick look at the engineering philosophy as we are both very familiar with the Oz operating and regulatory environment.
Two other thoughts ..
(a) don't forget that the runway slope might just catch up with and smite the aircraft for WAT conditions ..
(b) what does your company do about the third segment acceleration in this general T/O analysis case ?
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John, many thanks for the reply. I thoroughly agree with your assessment on general knowledge, which is why I'm trying to get a bit more info before suggesting the company fix it. I certainly would've expected that the ops manual would pass professional scrutiny, and was produced using engineered data. Expectation vs reality may differ. This is also why I'm being obtuse about the aircraft type and operator, so let's say it's all generic....
I didn't give the whole flow for determining max TO weight, just the parts that related to post-takeoff segments. There are corrections to TODA for runway slope, which will obviously alter the runway limited weight.
My thoughts (and only mine at this stage) on the 60m is that it's the standard length of a clearway, and nothing more.
As for corrected TORA vs TODA, partially my bad. The flow chart is headed "corrected TORA" (which is wrong), but the small print is correct that a corrected TODA is produced. I'll amend the first post for clarity.
At the end of day, I want (and fully expect) a fool-proof procedure written down that firstly keeps me completely safe, doesn't bust any rules and lastly allows me to haul out the max weight. I think the current way of doing business leans a bit more to the end point, and sacrifices the margins of the first.
I didn't give the whole flow for determining max TO weight, just the parts that related to post-takeoff segments. There are corrections to TODA for runway slope, which will obviously alter the runway limited weight.
My thoughts (and only mine at this stage) on the 60m is that it's the standard length of a clearway, and nothing more.
As for corrected TORA vs TODA, partially my bad. The flow chart is headed "corrected TORA" (which is wrong), but the small print is correct that a corrected TODA is produced. I'll amend the first post for clarity.
At the end of day, I want (and fully expect) a fool-proof procedure written down that firstly keeps me completely safe, doesn't bust any rules and lastly allows me to haul out the max weight. I think the current way of doing business leans a bit more to the end point, and sacrifices the margins of the first.
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Ex Douglas Driver,
My thoughts (and only mine at this stage) on the 60m is that it's the standard length of a clearway, and nothing more.
Standard stopway (RESA) .. clearway varies according to the airport and runway.
I want (and fully expect) a fool-proof procedure ...
Probably no such thing (due to most of us being fools from time to time) but the goal is admirable. Likewise, complete safety doesn't exist .. only levels of hazard and periods of exposure.
However .. a good attitude makes a good place to start ..
My thoughts (and only mine at this stage) on the 60m is that it's the standard length of a clearway, and nothing more.
Standard stopway (RESA) .. clearway varies according to the airport and runway.
I want (and fully expect) a fool-proof procedure ...
Probably no such thing (due to most of us being fools from time to time) but the goal is admirable. Likewise, complete safety doesn't exist .. only levels of hazard and periods of exposure.
However .. a good attitude makes a good place to start ..
Moderator
Ex Douglas Driver,
Now that I've had a look at your edits, the first segment distance consideration depends on the aircraft Type (gear retraction times) and the day ... better performance, more D1, lower performance, less D1.
For those who find this a bit strange .. first segment is that bit of the takeoff from 35ft to the completion of gear retraction .. if today it goes like a sports car, then you will be through 35ft fairly quickly, leaving a greater time for the completion of the (nominally constant) gear retraction cycle time and a corresponding longer D1 .. if, on the other hand, it's a dog .. then most, or all, of the retraction will be completed by 35 ft and there will be little or no remaining retraction cycle part to worry about ..
It follows that some aircraft don't have much of a first segment. The 60m/20m in your post could well be fine .. but some aircraft have 2000 ft plus D1 to contend with.
As this segment is very much a lower gradient than the second segment, runway slopes and obstacles in the immediate takeoff region become quite focussing for the ops engineering folk and, one hopes, the guys and gals in the sharp end.
Now that I've had a look at your edits, the first segment distance consideration depends on the aircraft Type (gear retraction times) and the day ... better performance, more D1, lower performance, less D1.
For those who find this a bit strange .. first segment is that bit of the takeoff from 35ft to the completion of gear retraction .. if today it goes like a sports car, then you will be through 35ft fairly quickly, leaving a greater time for the completion of the (nominally constant) gear retraction cycle time and a corresponding longer D1 .. if, on the other hand, it's a dog .. then most, or all, of the retraction will be completed by 35 ft and there will be little or no remaining retraction cycle part to worry about ..
It follows that some aircraft don't have much of a first segment. The 60m/20m in your post could well be fine .. but some aircraft have 2000 ft plus D1 to contend with.
As this segment is very much a lower gradient than the second segment, runway slopes and obstacles in the immediate takeoff region become quite focussing for the ops engineering folk and, one hopes, the guys and gals in the sharp end.
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767 Flight Study Guide
If both segments were to be applied, then first segment would be more limiting in having to consider the (S)TODA gradient against first segment performance. But this is not what Mr Boeing says....
This is not the aircraft type I was talking about in my first posts, but is taken directly from notes I've got (acquired from a large Australian carrier).
There must be another pilot who can give me an example of their flow chart for determining Max brakes release weight, when all you have to use for the calculation is published runway (S)TODA data and the flight manual. Does any other operator correct (S)TODA to "protect" the first climb segment?
Climb (Segment) Requirements and Terrain Clearance
The B767-200 is only limited, concerning climb requirements, by either the second segment requirements or terrain clearance requirements.
The B767-200 is only limited, concerning climb requirements, by either the second segment requirements or terrain clearance requirements.
Systems Used to Find Maximum Take-Off Weight With Obstacles
1. ....e.g. If the aircraft is capable of attaining 35ft within (say) the 2.2% supplementary take-off distance available (with engine failure at V1) and can attain at least a 2.2% net gradient of climb in the 2nd segment, then it will obviously clear the obstructions. my bold
1. ....e.g. If the aircraft is capable of attaining 35ft within (say) the 2.2% supplementary take-off distance available (with engine failure at V1) and can attain at least a 2.2% net gradient of climb in the 2nd segment, then it will obviously clear the obstructions. my bold
This is not the aircraft type I was talking about in my first posts, but is taken directly from notes I've got (acquired from a large Australian carrier).
There must be another pilot who can give me an example of their flow chart for determining Max brakes release weight, when all you have to use for the calculation is published runway (S)TODA data and the flight manual. Does any other operator correct (S)TODA to "protect" the first climb segment?
Last edited by Ex Douglas Driver; 2nd May 2006 at 12:42.
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Issue 5 of CAO 20.7.1B seems to have tried to shed a little more light on the regulatory requirements of Obstacle Clearance Requirements, over and above that required for the Takeoff Climb Requirements.
No issues with that.
That's what I'm trying to use.
OK - this says that segment 1 MUST be considered as part of the obstacle clearance requirements.
So this brings me back to whether the factors given are an accurate way of moving the end of the 1st segment back to over the runway.
12 OBSTACLE CLEARANCE REQUIREMENTS
12.1 For the purposes of subparagraph 4.1 (ba), the take-off obstacle clearance requirements are met if the net flight path of the aeroplane, following failure of the critical engine so that it is recognised at V1 appropriate to a dry runway, would clear by at least 35 feet vertically all obstacles in the take-off area.
12.1 For the purposes of subparagraph 4.1 (ba), the take-off obstacle clearance requirements are met if the net flight path of the aeroplane, following failure of the critical engine so that it is recognised at V1 appropriate to a dry runway, would clear by at least 35 feet vertically all obstacles in the take-off area.
12.3.1 For paragraph 12.1, an obstacle-clear take-off gradient, for a runway and a direction, published in Aeronautical Information Publications, may be used for the part of the take-off area commencing at the end of the take-off distance available and extending for the length of the surveyed area on which the gradient is based, despite the fact that the rate of divergence of the surveyed area may be less than 0.125D and that the length of the inner edge of the surveyed area may be less than 300 feet.
12.3.2 The requirements mentioned in paragraph 12.1 are met for a part of the takeoff area if the gradient of the net flight path in that part is not less than the obstacle-clear take-off gradient.
So this brings me back to whether the factors given are an accurate way of moving the end of the 1st segment back to over the runway.
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Points to note.
(a) 12.1 steers the calculation to a discrete obstacle analysis while 12.3.1 provides an acceptable alternative (provided one considers the intention of 12.1)
(b) there may or may not be a first segment. If there is one, then it has to be considered in the obstacle analysis
(c) The B767-200 is only limited, concerning climb requirements.. refers, I suggest, to WAT climb gradients only which are considered independent of obstacle clearance calculations
(d) Systems Used to Find Maximum Take-Off Weight With Obstacles .. can be true IF AND ONLY IF (and I would be very surprised if the particular large Australian carrier to which you refer got something so simple wrong) ..
(i) there is no first segment, and
(ii) the third segment acceleration phase is scheduled at a gross height such that the net third segment height clears all obstacles by 35/50 ft as necessary. This is a major failing by many when using the ERSA RDS data as it is too, too easy just to ignore the third segment and, potentially, run into a bumpy bit, depending on the length of the third segment .. simple geometry at work here
(e) as discussed earlier, the distance deltas which you quote are very specific to the Type and a generalisation, absolutely, is invalid
(f) we could go into a whole raft of different flowcharts dependent on various typical AFM protocols (and there are many varied ways of doing the AFM presentation business) .. suggest you restrict your question to a particular style of AFM presentation and a number of us can give you the story according to how it should be done ...
(a) 12.1 steers the calculation to a discrete obstacle analysis while 12.3.1 provides an acceptable alternative (provided one considers the intention of 12.1)
(b) there may or may not be a first segment. If there is one, then it has to be considered in the obstacle analysis
(c) The B767-200 is only limited, concerning climb requirements.. refers, I suggest, to WAT climb gradients only which are considered independent of obstacle clearance calculations
(d) Systems Used to Find Maximum Take-Off Weight With Obstacles .. can be true IF AND ONLY IF (and I would be very surprised if the particular large Australian carrier to which you refer got something so simple wrong) ..
(i) there is no first segment, and
(ii) the third segment acceleration phase is scheduled at a gross height such that the net third segment height clears all obstacles by 35/50 ft as necessary. This is a major failing by many when using the ERSA RDS data as it is too, too easy just to ignore the third segment and, potentially, run into a bumpy bit, depending on the length of the third segment .. simple geometry at work here
(e) as discussed earlier, the distance deltas which you quote are very specific to the Type and a generalisation, absolutely, is invalid
(f) we could go into a whole raft of different flowcharts dependent on various typical AFM protocols (and there are many varied ways of doing the AFM presentation business) .. suggest you restrict your question to a particular style of AFM presentation and a number of us can give you the story according to how it should be done ...
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Ex Douglas Driver,
I see here a thinking individual who is a little concerned about 1st segment considerations within the Australian system of RDS distances and gradients. A very valid concern. In the creation of RTOWs we typically use the Type ‘A’ runway charts and survey maps for the areas beyond the Type ‘A’ areas, and sometimes STODs and TODA to create obstacle polygons (Not my original idea, I have John_Tullamarine to thank for that gem). In so doing, we can assess the 1st segment obstacle clearance against ‘real’ data for real obstacles at real distances. As you have pointed out, when the RTOW is invalidated for any reason, a ‘fall back’ system is required for the pilot to calculate his own revised RTOW from TODA and STODs, and discrete obstacle data is not available.
The means that I use (and I’m sure that there are others), is to provide data for reduction of TODA and STODs to ensure that the 1st segment always lies above the runway and the obstacle-clear gradient for the STOD under consideration. What I describe here was approved by CASA for the operations for which I do P/E work, you will need approval......
This will not be a small project to use for a ‘one-off’ occasion, the work is far too much for that. Once produced, the table may be applied at any time that the RTOW is invalidated and you have to revert to the published RDS data. Whilst producing an obstacle polygon will give you the best performance, this data is runway specific and time consuming, and you will be far better served to develop a system which may be applied generically for all runways. You will need 4 essential items of information, i.e.
(1) The Runway Slope (RDS),
(2) The STODs and / or TODA Obstacle-Clear Gradients (RDS),
(3) The horizontal length of the 1st segment (AFM),
(4) The greatest difference between 1st and 2nd segment gradients for all Weights, Temperatures, and Pressure Heights (AFM).
Item (4) is the one that will be very time consuming, but you will find after the first few hundred 1st Vs 2nd segment gradient comparisons, that the difference is quite constant. Obtain the largest gradient delta as your base figure, this will cover your worst case scenario, so it can be used in all cases. Let’s call this gradient differential ‘DELTA’. Convert DELTA to degrees, where the angle = ATN(Gradient/100). Let’s call this angle ‘A’.
Next, from the AFM, find the 1st Segment horizontal distance. This will be quite constant even with weight variation, as it is based upon time of gear retraction, and the distance covered during retraction. If the AFM does not give you this, go to the ‘Close in Obstacle’ table, and extract the distance from reference zero to the end of the 1st segment (the point where the line suddenly bends upwards). Let’s call this distance S1D.
Now, subtract DELTA from the STOD Gradient to be used (1.6%, 1.9%, 2.2% etc.). This is the ‘safe’ 1st segment gradient to cover all cases. Let’s call it S1G.
IMPORTANT – As part of the 1st segment will now be flown above the runway, S1G must equal or exceed the runway slope. If it is less than the Slope, calculate the limiting weight for the runway slope as the 1st segment weight limit, and don’t worry about the 2nd segment as the actual gradient will exceed it. e.g. on Melbourne RWY 34 where the slope is +0.9%, calculate the 1st segment limiting weight for +0.9% or more (I ensure a minimum of 0.4% 1st segment gradient in my work, thus, on Melbourne RWY 34 I would ensure a 1.3% 1st segment gradient capability). Back to the main story……
Now, find the gradient and angle that the 1st segment achieves above the runway from the formula : S1G minus SLOPE, where Down Slope is Negative, and Up Slope is Positive. Convert this to degrees, and let’s call this angle S1A.
Now, we have 3 important values to compute, namely :
S1A : The Angle that the 1st Segment makes above the runway,
S1D : The horizontal length of the 1st Segment, and
A : The angular difference for the worst case comparison between 1st and 2nd segment angles.
Now, it’s a straight-forward calculation to find the REDUCTION in STOD or TODA length to ensure that the 1st segment remains above both the runway and the Obstacle-Clear Gradient :
REDUCTION = S1D X Sin A / Sin (180 – A – S1A)
Now, repeat it again and again and create a Runway Slope / OCG table for use with any set of RDS data.
Easy isn’t it? Now that you have the reduction, subtract it from the TODA or STOD, and, as you’re using Balanced Field, if the answer is greater than TORA, use the TORA. Mutt would do that, but I suspect that John_Tullamarine and I would use up to TORA+60M if it was available.
An Example :
You’re working with a 2.5% STOD of 1500M. Runway Slope = + 0.3% (UP)
Maximum difference between 1st and 2nd segment gradients in all AFM data is 0.9%.
1st Segment Distance (S1D) = 700 M
DELTA = 0.9 : Angle ‘A’ = ATN (0.9/100) = 0.515648°
For a 2.5% STOD, S1G = 2.5 – 0.9 = 1.6%
Gradient to Runway = S1G minus SLOPE = 1.6 – 0.3 = 1.3% : S1A = 0.744803°
Substituting into the formula REDUCTION = S1D X Sin A / Sin (180 – A – S1A),
REDUCTION = 700 X Sin 0.515648° / Sin (180° - 0.515648° - 0.744803°) = 286.4 M
Useable STOD Distance = 1500 M – 286.4 M = 1213.6 M
A piece of cake.
Hey John_Tullamarine, you worked for XXXX airlines also? So did I, along with about 7,631 other Prooners who wish to remain anonymous. Ummm, there is one chess piece embedded here
Regards,
Old Smokey
I see here a thinking individual who is a little concerned about 1st segment considerations within the Australian system of RDS distances and gradients. A very valid concern. In the creation of RTOWs we typically use the Type ‘A’ runway charts and survey maps for the areas beyond the Type ‘A’ areas, and sometimes STODs and TODA to create obstacle polygons (Not my original idea, I have John_Tullamarine to thank for that gem). In so doing, we can assess the 1st segment obstacle clearance against ‘real’ data for real obstacles at real distances. As you have pointed out, when the RTOW is invalidated for any reason, a ‘fall back’ system is required for the pilot to calculate his own revised RTOW from TODA and STODs, and discrete obstacle data is not available.
The means that I use (and I’m sure that there are others), is to provide data for reduction of TODA and STODs to ensure that the 1st segment always lies above the runway and the obstacle-clear gradient for the STOD under consideration. What I describe here was approved by CASA for the operations for which I do P/E work, you will need approval......
This will not be a small project to use for a ‘one-off’ occasion, the work is far too much for that. Once produced, the table may be applied at any time that the RTOW is invalidated and you have to revert to the published RDS data. Whilst producing an obstacle polygon will give you the best performance, this data is runway specific and time consuming, and you will be far better served to develop a system which may be applied generically for all runways. You will need 4 essential items of information, i.e.
(1) The Runway Slope (RDS),
(2) The STODs and / or TODA Obstacle-Clear Gradients (RDS),
(3) The horizontal length of the 1st segment (AFM),
(4) The greatest difference between 1st and 2nd segment gradients for all Weights, Temperatures, and Pressure Heights (AFM).
Item (4) is the one that will be very time consuming, but you will find after the first few hundred 1st Vs 2nd segment gradient comparisons, that the difference is quite constant. Obtain the largest gradient delta as your base figure, this will cover your worst case scenario, so it can be used in all cases. Let’s call this gradient differential ‘DELTA’. Convert DELTA to degrees, where the angle = ATN(Gradient/100). Let’s call this angle ‘A’.
Next, from the AFM, find the 1st Segment horizontal distance. This will be quite constant even with weight variation, as it is based upon time of gear retraction, and the distance covered during retraction. If the AFM does not give you this, go to the ‘Close in Obstacle’ table, and extract the distance from reference zero to the end of the 1st segment (the point where the line suddenly bends upwards). Let’s call this distance S1D.
Now, subtract DELTA from the STOD Gradient to be used (1.6%, 1.9%, 2.2% etc.). This is the ‘safe’ 1st segment gradient to cover all cases. Let’s call it S1G.
IMPORTANT – As part of the 1st segment will now be flown above the runway, S1G must equal or exceed the runway slope. If it is less than the Slope, calculate the limiting weight for the runway slope as the 1st segment weight limit, and don’t worry about the 2nd segment as the actual gradient will exceed it. e.g. on Melbourne RWY 34 where the slope is +0.9%, calculate the 1st segment limiting weight for +0.9% or more (I ensure a minimum of 0.4% 1st segment gradient in my work, thus, on Melbourne RWY 34 I would ensure a 1.3% 1st segment gradient capability). Back to the main story……
Now, find the gradient and angle that the 1st segment achieves above the runway from the formula : S1G minus SLOPE, where Down Slope is Negative, and Up Slope is Positive. Convert this to degrees, and let’s call this angle S1A.
Now, we have 3 important values to compute, namely :
S1A : The Angle that the 1st Segment makes above the runway,
S1D : The horizontal length of the 1st Segment, and
A : The angular difference for the worst case comparison between 1st and 2nd segment angles.
Now, it’s a straight-forward calculation to find the REDUCTION in STOD or TODA length to ensure that the 1st segment remains above both the runway and the Obstacle-Clear Gradient :
REDUCTION = S1D X Sin A / Sin (180 – A – S1A)
Now, repeat it again and again and create a Runway Slope / OCG table for use with any set of RDS data.
Easy isn’t it? Now that you have the reduction, subtract it from the TODA or STOD, and, as you’re using Balanced Field, if the answer is greater than TORA, use the TORA. Mutt would do that, but I suspect that John_Tullamarine and I would use up to TORA+60M if it was available.
An Example :
You’re working with a 2.5% STOD of 1500M. Runway Slope = + 0.3% (UP)
Maximum difference between 1st and 2nd segment gradients in all AFM data is 0.9%.
1st Segment Distance (S1D) = 700 M
DELTA = 0.9 : Angle ‘A’ = ATN (0.9/100) = 0.515648°
For a 2.5% STOD, S1G = 2.5 – 0.9 = 1.6%
Gradient to Runway = S1G minus SLOPE = 1.6 – 0.3 = 1.3% : S1A = 0.744803°
Substituting into the formula REDUCTION = S1D X Sin A / Sin (180 – A – S1A),
REDUCTION = 700 X Sin 0.515648° / Sin (180° - 0.515648° - 0.744803°) = 286.4 M
Useable STOD Distance = 1500 M – 286.4 M = 1213.6 M
A piece of cake.
Hey John_Tullamarine, you worked for XXXX airlines also? So did I, along with about 7,631 other Prooners who wish to remain anonymous. Ummm, there is one chess piece embedded here
Regards,
Old Smokey
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A PS to the post that I just made (because editing tends to disturb the format)............
Recommended to NOT use this technique in Tailwind conditions, which extend the 1st segment distance and reduce the gradient. Any Headwind is, of course, a bonus.
Using this 'fall back' data errs on the conservative side (Good! ), achieving for my main client a 44 ft screen height in lieu of the required 35 ft. 'My' CASA guy likes that, so do I.
Regards,
Old Smokey
Recommended to NOT use this technique in Tailwind conditions, which extend the 1st segment distance and reduce the gradient. Any Headwind is, of course, a bonus.
Using this 'fall back' data errs on the conservative side (Good!
), achieving for my main client a 44 ft screen height in lieu of the required 35 ft. 'My' CASA guy likes that, so do I.Regards,
Old Smokey
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Old Smokey
Many thanks for the info - I really appreciate your time. It'll give me at least a confidence check on the data provided.
Ex DD
It's been a very slow few weeks!!
Many thanks for the info - I really appreciate your time. It'll give me at least a confidence check on the data provided.
Ex DD
It's been a very slow few weeks!!
Moderator
OS,
Missed the chess move .. unless it was the reference to the large carrier ?
Used a similar approach for a while but gave it away for one-offs in preference to the G1 or D1 sledgehammer techniques for simplicity .. and comfort (mine) ... this sort of analysis can be beset by differences of small numbers problems ..
In any case, use of this approach would normally be by means of a standard STODA/TODA correction in the ops manual so there should be no need for the pilot to do other than apply a declared (albeit conservative) correction for the particular Type/configuration ?
A few thoughts/questions ..
(a) I presume that you address the H3 problems by some other rational means for crew use in the field ?
(b) What is the rationale for your running with a 0.4 margin on G1 ?
(c) You could also consider simplifying the expression and procedure a little by replacing
180 - A - S1A
with the equivalent
180 + runway slope - STODA slope
which might help a bit with potential differences errors.
Re TORA and TORA+60, pragmatism dictates the latter, but from a regulatory viewpoint, I would want Regulator concurrence otherwise I would go for the TORA declared value.
Isn't this all jolly good fun ... ?
Missed the chess move .. unless it was the reference to the large carrier ?
Used a similar approach for a while but gave it away for one-offs in preference to the G1 or D1 sledgehammer techniques for simplicity .. and comfort (mine) ... this sort of analysis can be beset by differences of small numbers problems ..
In any case, use of this approach would normally be by means of a standard STODA/TODA correction in the ops manual so there should be no need for the pilot to do other than apply a declared (albeit conservative) correction for the particular Type/configuration ?
A few thoughts/questions ..
(a) I presume that you address the H3 problems by some other rational means for crew use in the field ?
(b) What is the rationale for your running with a 0.4 margin on G1 ?
(c) You could also consider simplifying the expression and procedure a little by replacing
180 - A - S1A
with the equivalent
180 + runway slope - STODA slope
which might help a bit with potential differences errors.
Re TORA and TORA+60, pragmatism dictates the latter, but from a regulatory viewpoint, I would want Regulator concurrence otherwise I would go for the TORA declared value.
Isn't this all jolly good fun ... ?
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John_T,
I just typed a reply to your questions, the length of which rivaled my last post. I took too long, and my sign-in timed out! Danny, we need more time!!!
Gotta hit the sack for an early morning aviation commitment, but in brief - the 60M additive to TORA (Provided that 60M or more of Clearway is available) is accounting for the airborne portion of the Takeoff from Vloff to V2, and the 50% requirement above the runway. And Yes, it is with the manufacturer's and CASA's approval upon official provision of the 'worst case' distance for this manoeuvre.
I just hope that I can remember all the other things that I said for when I get back and can answer you properly. In the mean-time, the mention of the 50% rule should arouse a few JAR-25'ers
To your first question, no, we were competitors in a previous life, a tongue in cheek reference to the generic XXXX airlines of your moderatorial insertion a few posts ago.
Regards,
Old Smokey
I just typed a reply to your questions, the length of which rivaled my last post. I took too long, and my sign-in timed out! Danny, we need more time!!!
Gotta hit the sack for an early morning aviation commitment, but in brief - the 60M additive to TORA (Provided that 60M or more of Clearway is available) is accounting for the airborne portion of the Takeoff from Vloff to V2, and the 50% requirement above the runway. And Yes, it is with the manufacturer's and CASA's approval upon official provision of the 'worst case' distance for this manoeuvre.
I just hope that I can remember all the other things that I said for when I get back and can answer you properly. In the mean-time, the mention of the 50% rule should arouse a few JAR-25'ers
To your first question, no, we were competitors in a previous life, a tongue in cheek reference to the generic XXXX airlines of your moderatorial insertion a few posts ago.
Regards,
Old Smokey
Moderator
OS,
.. and then, under the old UK rules, I always could see a little anxiety with 1:2 and a TOR-limited takeoff ..
Ah, I see it now ... red versus blue .. all a long time ago, now.
.. and then, under the old UK rules, I always could see a little anxiety with 1:2 and a TOR-limited takeoff ..
Ah, I see it now ... red versus blue .. all a long time ago, now.
Moderator
(As I did ..) ... it occurred to me that others might be doing a back of a fag packet derivation of OS' formula. If so a couple of points might make it a bit easier to derive .. (if you are playing with TODA, then replace STODA by TODA) ..
(a) draw a sketch of the runway slope with the STODA gradients. (Apologies for no sketch to make it easier but I don't have the facility on this machine)
(b) the presumption is that the second segment gradient is driven to equal the STODA gradient, so draw the first segment from the runway to intersect the STODA gradient. OS has suggested that you use the critical difference between the second and first segments .. that's fine as the difference is pretty constant, however, as you need to check the AFM for the first segment distance, you might just as well use the actual first segment gradient for the calculation .. keep in mind that this is all going on the background as part of generating a table of some sort for the pilot to use ..
(c) in the triangle bounded by
(i) the distance delta (D) to be found
(ii) STODA surface from the runway to the intersection with first segment gradient
(iii) first segment slant distance (d)
the angles are
(i) first segment gradient - runway slope (= G1-GR)
(ii) STODA slope - first segment slope (= GS-G1)
(iii) 180 - (G1-GR) - (GS-G1) .... (sum of angles is 180 degrees)
Sine rule gives ..
D = d/cos(G1) * sin(GS-G1)/sin(180 - (G1-GR) - (GS-G1))
putting cos(G1) = 1 (error in OS' example is a whole 4 cm) gives OS' formula.
The divisor term can be simplified by expanding bracket expressions to get
D = d * sin(GS-G1)/sin(180+GR-GS)
(keep in mind, if you are playing with Excel or similar to do the sums, that you need to convert between radians and degrees for calculations ..)
The preceding presumes that I have counted on all my fingers correctly along the way ....
(a) draw a sketch of the runway slope with the STODA gradients. (Apologies for no sketch to make it easier but I don't have the facility on this machine)
(b) the presumption is that the second segment gradient is driven to equal the STODA gradient, so draw the first segment from the runway to intersect the STODA gradient. OS has suggested that you use the critical difference between the second and first segments .. that's fine as the difference is pretty constant, however, as you need to check the AFM for the first segment distance, you might just as well use the actual first segment gradient for the calculation .. keep in mind that this is all going on the background as part of generating a table of some sort for the pilot to use ..
(c) in the triangle bounded by
(i) the distance delta (D) to be found
(ii) STODA surface from the runway to the intersection with first segment gradient
(iii) first segment slant distance (d)
the angles are
(i) first segment gradient - runway slope (= G1-GR)
(ii) STODA slope - first segment slope (= GS-G1)
(iii) 180 - (G1-GR) - (GS-G1) .... (sum of angles is 180 degrees)
Sine rule gives ..
D = d/cos(G1) * sin(GS-G1)/sin(180 - (G1-GR) - (GS-G1))
putting cos(G1) = 1 (error in OS' example is a whole 4 cm) gives OS' formula.
The divisor term can be simplified by expanding bracket expressions to get
D = d * sin(GS-G1)/sin(180+GR-GS)
(keep in mind, if you are playing with Excel or similar to do the sums, that you need to convert between radians and degrees for calculations ..)
The preceding presumes that I have counted on all my fingers correctly along the way ....
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Hi John_Tullamarine,
This thread is running a bit cold now, but to address the questions posed in you recent post…………
Yup, Red Vs Blue, you got it in one, the chess piece was (and is) a bit more cryptic.
I can agree with you that for the odd-ball occasions where an RTOW is invalidated a simple (and comfortable) single deduction to STOD/TODA might be desirable, but, oh boy!, the variation is enormous even for the same OCG and S1 length, for a variety of Runway slopes. As has been covered (by both of us in fact), when discrete analysis is unavailable and we have to revert to RDS data ‘on the day’ we need to keep the 1st segment above the Runway and the OCP, but what of considerations for steeply sloping runways. Your namesake’s RWY 34 comes to mind here. As we’ve both pontificated, S1 length and Delta G1/G2 is quite constant, and even the use of the worst case data here will only be a minor penalty if applied to the best case. The big factor in this one is the runway slope. Irrespective of the geometric techniques used, a simple one page table of RWY Slope Vs OCG does it all, including the steep runway slope case. (I’d love to post an example here but there goes the anonymity).
H3 problems for the odd-ball days are monitored by ‘Ops Watch’ in my absence, I’ve provided them with a table of highest tolerable obstacles for each runway procedure and the closed (not open) areas that the Takeoff Area covers beyond the worst S2 distance. We use a standard 1000 ft AFL H3, and as most MAA’s are well below this, operational restrictions are rare. If the ‘new’ obstacle is higher than that listed, I get a phone call. I don’t get many phone calls. When the MAA is above 1000 ft (e.g. Albury RWY 07) and a new lump appears, I get a phone call. Similar procedures apply for S2 in the area not covered by Type’A’ charts or the RDS surveyed area.
The 0.4% margin on G1…. Lines drawn in the sand (by me). I cannot accept the allowance that G1 need only be positive (both aircraft that I answer to CASA for are 2 engined), and the line drawn in the sand is the minimum 1.2% capability required throughout the OEI procedure degraded by the 2 engined aircraft decrement of 0.8%, et voila! 0.4%. In it’s application, G1 minimum must be 0.4% to the horizontal, G1 OCP plus 0.4%, or Runway Slope plus 0.4%, whichever is the greater. In practice, it’s rarely limiting. “My” 2 aircraft have about a 0.9% Delta G1/G2, and as we’re often looking at a minimum Net G2 of 1.6%, at least 0.7% is achieved in any case….. except at your namesake’s 34.
Re TORA and TORA+60…… Another line drawn in the sand, but with manufacturer and CASA concurrence. A bit of simplification at work here, TORA+60M is used as the maximum useable ASDA to preserve the RESA. Protection is needed for the continued Takeoff to ensure that 50% of the airborne portion from Vloff to V2 be over the TORA, and in the interests of simplification and commonality with the ASDA case, 60M use of the Clearway was considered. AFM data from the manufacturer was virtually non-existent here, but I was successful in gaining an official (FAA approved) statement from both manufacturers that Vloff to V2 was ALWAYS more than 120M in any set of circumstances, thus, ‘my’ CASA guy accepted the 60M use of Clearway. Thus, the greatest credit taken for Stopway or Clearway is 60M.
Thanks for the simplified geometric calculation, Yep, it works the same, but as I did my original post developed it on a piece of paper beside me as I typed the post (too lazy to dig through my programmes). I’m always worried when throwing formulae at people not using mathematics every day to exercise great care with Gradient, Gradians, Radians, and Degrees, which is why I went through the more laborious process of first converting everything to degrees. You always could simplify to a simple one-liner couldn’t you? .
A bit of a thumb nail sketch, there’s much more, that’s the gist of it, includes a fair bit of personal policy to enable better sleeping habits by me.
Yes, it continues to be jolly good fun, does it not?
Regards,
Old Smokey
This thread is running a bit cold now, but to address the questions posed in you recent post…………
Yup, Red Vs Blue, you got it in one, the chess piece was (and is) a bit more cryptic.
I can agree with you that for the odd-ball occasions where an RTOW is invalidated a simple (and comfortable) single deduction to STOD/TODA might be desirable, but, oh boy!, the variation is enormous even for the same OCG and S1 length, for a variety of Runway slopes. As has been covered (by both of us in fact), when discrete analysis is unavailable and we have to revert to RDS data ‘on the day’ we need to keep the 1st segment above the Runway and the OCP, but what of considerations for steeply sloping runways. Your namesake’s RWY 34 comes to mind here. As we’ve both pontificated, S1 length and Delta G1/G2 is quite constant, and even the use of the worst case data here will only be a minor penalty if applied to the best case. The big factor in this one is the runway slope. Irrespective of the geometric techniques used, a simple one page table of RWY Slope Vs OCG does it all, including the steep runway slope case. (I’d love to post an example here but there goes the anonymity).
H3 problems for the odd-ball days are monitored by ‘Ops Watch’ in my absence, I’ve provided them with a table of highest tolerable obstacles for each runway procedure and the closed (not open) areas that the Takeoff Area covers beyond the worst S2 distance. We use a standard 1000 ft AFL H3, and as most MAA’s are well below this, operational restrictions are rare. If the ‘new’ obstacle is higher than that listed, I get a phone call. I don’t get many phone calls. When the MAA is above 1000 ft (e.g. Albury RWY 07) and a new lump appears, I get a phone call. Similar procedures apply for S2 in the area not covered by Type’A’ charts or the RDS surveyed area.
The 0.4% margin on G1…. Lines drawn in the sand (by me). I cannot accept the allowance that G1 need only be positive (both aircraft that I answer to CASA for are 2 engined), and the line drawn in the sand is the minimum 1.2% capability required throughout the OEI procedure degraded by the 2 engined aircraft decrement of 0.8%, et voila! 0.4%. In it’s application, G1 minimum must be 0.4% to the horizontal, G1 OCP plus 0.4%, or Runway Slope plus 0.4%, whichever is the greater. In practice, it’s rarely limiting. “My” 2 aircraft have about a 0.9% Delta G1/G2, and as we’re often looking at a minimum Net G2 of 1.6%, at least 0.7% is achieved in any case….. except at your namesake’s 34.
Re TORA and TORA+60…… Another line drawn in the sand, but with manufacturer and CASA concurrence. A bit of simplification at work here, TORA+60M is used as the maximum useable ASDA to preserve the RESA. Protection is needed for the continued Takeoff to ensure that 50% of the airborne portion from Vloff to V2 be over the TORA, and in the interests of simplification and commonality with the ASDA case, 60M use of the Clearway was considered. AFM data from the manufacturer was virtually non-existent here, but I was successful in gaining an official (FAA approved) statement from both manufacturers that Vloff to V2 was ALWAYS more than 120M in any set of circumstances, thus, ‘my’ CASA guy accepted the 60M use of Clearway. Thus, the greatest credit taken for Stopway or Clearway is 60M.
Thanks for the simplified geometric calculation, Yep, it works the same, but as I did my original post developed it on a piece of paper beside me as I typed the post (too lazy to dig through my programmes). I’m always worried when throwing formulae at people not using mathematics every day to exercise great care with Gradient, Gradians, Radians, and Degrees, which is why I went through the more laborious process of first converting everything to degrees. You always could simplify to a simple one-liner couldn’t you?
.A bit of a thumb nail sketch, there’s much more, that’s the gist of it, includes a fair bit of personal policy to enable better sleeping habits by me.
Yes, it continues to be jolly good fun, does it not?
Regards,
Old Smokey