Declared Conditions, calculating t/off & landing distances
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Declared Conditions, calculating t/off & landing distances
In all the books I have about flying up to CPL, I cannot find a proper thorough guide to using the declared charts in CAO 20.7 (appendix)
We use the charts to find the declared conditions, add the elevation... All books state this, but....
Then what?
What do we do with that density height figure?
What do we do if our POH has Pressure height & temperature only in the performance section?
Bear with me because I have been doing it one way which I'll explain, but was recently introduced to another way by another "Bobby" who then told me another "Birdy" does it yet another way!!!
I was taught to to this way, which I'll call "my way" ( not that I invented this, it was taught to me, however, I will stand corrected )
1. Obtain the declared height (say 2500')
2. Add the Elevation (say 1500')
3. With this DH of 4000', I would use in the POH as pressure height intersecting with the corresponding ISA temperature at 4000' which is 7º
4. read off the table the take-off or landing distance.
This next way, I'll call "Bobby's way"
1 & 2 steps - same as above
3. The elevation is 1500' then the temp bobby would use is 12º - this temp came from a standard atmosphere SL temp of 15º corrected for the elevation, ie SL standard temp, less 3º for the 1500' elevation
4. Using 4000 PH on the POH table, read off the distances that intersect with 12º
Finally "Birdy's way"
1 & 2 steps - same as above
3. The elevation is 1500' birdy uses 15º - the standard SL temp
4. Using 4000 PH on the POH table, Birdy reads off the distances that intersect with 15º
"My way" is what I've been using forever (DH4000' convert to PH4000' using ISA 7º at that DH)
"Bobby's way" is slightly safer as the temp is higher (PH4000' 12º)
"Birdy's way" - safer again using a higher temp (PH4000' 15º)
Which way do you use?
Where is a good resource to refer, ATC, Bob Tait dont fully discuss this...
We use the charts to find the declared conditions, add the elevation... All books state this, but....
Then what?
What do we do with that density height figure?
What do we do if our POH has Pressure height & temperature only in the performance section?
Bear with me because I have been doing it one way which I'll explain, but was recently introduced to another way by another "Bobby" who then told me another "Birdy" does it yet another way!!!
I was taught to to this way, which I'll call "my way" ( not that I invented this, it was taught to me, however, I will stand corrected )
1. Obtain the declared height (say 2500')
2. Add the Elevation (say 1500')
3. With this DH of 4000', I would use in the POH as pressure height intersecting with the corresponding ISA temperature at 4000' which is 7º
4. read off the table the take-off or landing distance.
This next way, I'll call "Bobby's way"
1 & 2 steps - same as above
3. The elevation is 1500' then the temp bobby would use is 12º - this temp came from a standard atmosphere SL temp of 15º corrected for the elevation, ie SL standard temp, less 3º for the 1500' elevation
4. Using 4000 PH on the POH table, read off the distances that intersect with 12º
Finally "Birdy's way"
1 & 2 steps - same as above
3. The elevation is 1500' birdy uses 15º - the standard SL temp
4. Using 4000 PH on the POH table, Birdy reads off the distances that intersect with 15º
"My way" is what I've been using forever (DH4000' convert to PH4000' using ISA 7º at that DH)
"Bobby's way" is slightly safer as the temp is higher (PH4000' 12º)
"Birdy's way" - safer again using a higher temp (PH4000' 15º)
Which way do you use?
Where is a good resource to refer, ATC, Bob Tait dont fully discuss this...
Density is just pressure corrected for temp, so the first method would be the correct one if you are using the figures off the declared density altitude charts. If the temp has no deviation from ISA, the PA=DA.
These charts are (same as your take-off question) worst case scenario and are used where a TAF or observed conditions are not available.
If you are at the aerodrome, setting 1013 on your altimeter will give you the pressure altitude and you can get the temp off the aircraft's OAT gauge.
These charts are (same as your take-off question) worst case scenario and are used where a TAF or observed conditions are not available.
If you are at the aerodrome, setting 1013 on your altimeter will give you the pressure altitude and you can get the temp off the aircraft's OAT gauge.
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We use the charts to find the declared conditions, add the elevation... All books state this, but....
Then what?
Then what?
The Australian set were specially printed, using data from "certification" flights that the aircraft type had to undertake in order to gain Australian "certification". Among other things, the Australian charts used the same distance factors across all aircraft types - the same factors that appear in CAO 20.7
Those charts allowed you to enter them directly with a density altitude. This is where those graphs of declared conditions came in.
Nowadays, new types entering Australia don't have to go through that "certification" process, and you may use the manufacturers performance charts.
Your way of using the declared conditions to arrive at a PA and temperature is the best. The other two methods are adding an unnecessary safety margin. There would already be several safety margins built into the figures you finally arrive at.
Moderator
(a) Then what? What do we do with that density height figure?
Guidance is provided in CAO 20.7.1.App 1 (2) and App 2 (2). The other Orders provide, variously, permissions to use the protocol.
Your technique is fine and accords with the CAO procedure.
(b) In the POH you would find the manufacturers charts, but in the flight manual would also be the Australian set, approved for use by the Australian regulator of the time
In the beginning, there were Certificates of Airworthiness, which included limitations and, subsequently performance requirements.
Eventually, the CofA became sufficiently unwieldy to warrant development of an adjunct document, the Flight Manual. For GA aircraft, the Australian Flight Manual was a bit of a perfunctory document and included the bare bones information. Those who flew pre-GAMA format manuals would be familiar with the old style flight manuals.
At some time (long before I came into the game in the 60s) DCA started issuing P-chart performance data. I suspect that the early heavy charts (DC3 etc) were the immediate precursors .. certainly, they were of a similar style. The P-charts were standardised in terms of equations and format and this was promulgated in internal DCA tech memo documents. If anyone is interested I should be able to dig out my copies from the dusty archives so that you can have the actual equations which we used back then. No reason why you can't apply them to the present POH data to provide whatever levels of conservatism you might consider useful.
The bulk of the GA charts you may have seen were done in accordance with a memo which was written by Ian C and Ronnie S in the late 60s/early 70s and was directed at piston aircraft. Due to some problems the Nomad had with the older standards, ANO 101.22 was revised to accommodate turboprop performance and a revised memo was raised by John F. However, due to the latter document's complexity - some big equations - the superseded memo (and ANO) continued to be used for piston aircraft - which made life easier for simple minded chaps like me ...
So far as flight testing was concerned, the OEMs tended to go for comparatively high cost, high accuracy tests for marketing driven reasons.
Typically, tests were recorded by cinetheodolite for analysis. This device was just a fancy combined movie camera with a parallel azimuth (for distance calculations) and elevation (for height calculations) trace recording unit. Analysis consisted of reading off the traces, doing the distance and height sums (the runway/cinetheodolite arrangement was surveyed prior to setup so it was just a bit of trig work), and applying small error corrections from the movie record to allow for camera mistracking of the aircraft during the takeoff or landing. Quite apart from distance data, one could figure out speeds and accelerations to a reasonable level of accuracy from the plotted distance/height against time traces.
This approach was a bit over the top for a C150 and similar ilk so the DCA technique was a very much cut down version involving some fixed cameras to estimate the 50ft distance point. Trust me, analysing a cinetheodolite series of tests was a right time-wasting and expensive pain.
Turned out that the average of several runs gave pretty reliable and repeatable data so it all worked out fine for comparatively little cost. The results were plugged into the memo equations and the usual graphs drawn up. You would have seen examples both of the DCA format and the more common correction carpet presentation .. both gave much the same utility for the pilot.
In the US market, previously, there had existed a range of flight/operations manuals/handbooks published by the various OEMs.
In the mid-70s GAMA (the General Aviation Manufacturers' Association) published a recommended, standardised, GA aircraft operating manual format (GAMA Specification No. 1, first issued 15 Feb 75). When the GAMA POH (which includes the FAA approved flight manual) came into vogue, DCA accepted that document (with some local additions) as a (far more useful) alternative to the old style DCA flight manual and we gradually saw a swing across to the GAMA manuals during the late 70s and into the early 80s.
So far as performance charts were concerned, the older style DCA charts were still required as the US document gave raw data and didn't include any of the ANO required fudge factors.
As an aside, ICAO subsequently published recommended formats for light aircraft and air service operations manuals (Doc 9516-AN/930 - Guidance on the Preparation of a Pilot's Operating Handbook for Light Aeroplanes, 1st edition, 1991 - which was generally similar to the GAMA document - and Doc 9376-AN/914, 1st Edition, 1990). [Having located the three documents in the dusty archives, I'll keep them to hand in case anyone needs to refer to specific words in future].
Generally, use of the GAMA manual removed the need for specific flight tests as the POH data was, itself, so based. DCA accepted selection of a few points from the POH data and those data were then plugged into the equation machine to produce the Australian charts for inclusion in the POH. Nothing to stop anyone doing some tests but I can't recall anyone doing so.
Subsequently, as part of the harmonisation process, the pendulum swing right across ... the GAMA manual was adopted in toto ... and the old DCA style charts were thrown out with the baby and the bathwater ...
(c) Among other things, the Australian charts used the same distance factors across all aircraft types
Sort of correct .. the use of these charts generally applied to the ANO 101.22 aircraft (lighties)
(d) This is where those graphs of declared conditions came in.
Bit off the mark here, I'm afraid. If we go back a long way, Australia was responsible for PNG and, given the poor performance capability of the earlier piston aircraft and the significant terrain in PNG, there arose a classification known as Developmental Air Services. (These predated my time and, while they would have been applicable to mainland activities, my understanding was that the driver was PNG operations). As far as I can see, apart from a legacy definition which somehow hasn't been culled from the CAO, DAS have gone the way of the dodo. Declared conditions were associated with these older operational standards.
(e) .. and you may use the manufacturers performance charts.
.. but do so with considerable circumspection .. presume that the POH data is barely achievable.
Guidance is provided in CAO 20.7.1.App 1 (2) and App 2 (2). The other Orders provide, variously, permissions to use the protocol.
Your technique is fine and accords with the CAO procedure.
(b) In the POH you would find the manufacturers charts, but in the flight manual would also be the Australian set, approved for use by the Australian regulator of the time
In the beginning, there were Certificates of Airworthiness, which included limitations and, subsequently performance requirements.
Eventually, the CofA became sufficiently unwieldy to warrant development of an adjunct document, the Flight Manual. For GA aircraft, the Australian Flight Manual was a bit of a perfunctory document and included the bare bones information. Those who flew pre-GAMA format manuals would be familiar with the old style flight manuals.
At some time (long before I came into the game in the 60s) DCA started issuing P-chart performance data. I suspect that the early heavy charts (DC3 etc) were the immediate precursors .. certainly, they were of a similar style. The P-charts were standardised in terms of equations and format and this was promulgated in internal DCA tech memo documents. If anyone is interested I should be able to dig out my copies from the dusty archives so that you can have the actual equations which we used back then. No reason why you can't apply them to the present POH data to provide whatever levels of conservatism you might consider useful.
The bulk of the GA charts you may have seen were done in accordance with a memo which was written by Ian C and Ronnie S in the late 60s/early 70s and was directed at piston aircraft. Due to some problems the Nomad had with the older standards, ANO 101.22 was revised to accommodate turboprop performance and a revised memo was raised by John F. However, due to the latter document's complexity - some big equations - the superseded memo (and ANO) continued to be used for piston aircraft - which made life easier for simple minded chaps like me ...
So far as flight testing was concerned, the OEMs tended to go for comparatively high cost, high accuracy tests for marketing driven reasons.
Typically, tests were recorded by cinetheodolite for analysis. This device was just a fancy combined movie camera with a parallel azimuth (for distance calculations) and elevation (for height calculations) trace recording unit. Analysis consisted of reading off the traces, doing the distance and height sums (the runway/cinetheodolite arrangement was surveyed prior to setup so it was just a bit of trig work), and applying small error corrections from the movie record to allow for camera mistracking of the aircraft during the takeoff or landing. Quite apart from distance data, one could figure out speeds and accelerations to a reasonable level of accuracy from the plotted distance/height against time traces.
This approach was a bit over the top for a C150 and similar ilk so the DCA technique was a very much cut down version involving some fixed cameras to estimate the 50ft distance point. Trust me, analysing a cinetheodolite series of tests was a right time-wasting and expensive pain.
Turned out that the average of several runs gave pretty reliable and repeatable data so it all worked out fine for comparatively little cost. The results were plugged into the memo equations and the usual graphs drawn up. You would have seen examples both of the DCA format and the more common correction carpet presentation .. both gave much the same utility for the pilot.
In the US market, previously, there had existed a range of flight/operations manuals/handbooks published by the various OEMs.
In the mid-70s GAMA (the General Aviation Manufacturers' Association) published a recommended, standardised, GA aircraft operating manual format (GAMA Specification No. 1, first issued 15 Feb 75). When the GAMA POH (which includes the FAA approved flight manual) came into vogue, DCA accepted that document (with some local additions) as a (far more useful) alternative to the old style DCA flight manual and we gradually saw a swing across to the GAMA manuals during the late 70s and into the early 80s.
So far as performance charts were concerned, the older style DCA charts were still required as the US document gave raw data and didn't include any of the ANO required fudge factors.
As an aside, ICAO subsequently published recommended formats for light aircraft and air service operations manuals (Doc 9516-AN/930 - Guidance on the Preparation of a Pilot's Operating Handbook for Light Aeroplanes, 1st edition, 1991 - which was generally similar to the GAMA document - and Doc 9376-AN/914, 1st Edition, 1990). [Having located the three documents in the dusty archives, I'll keep them to hand in case anyone needs to refer to specific words in future].
Generally, use of the GAMA manual removed the need for specific flight tests as the POH data was, itself, so based. DCA accepted selection of a few points from the POH data and those data were then plugged into the equation machine to produce the Australian charts for inclusion in the POH. Nothing to stop anyone doing some tests but I can't recall anyone doing so.
Subsequently, as part of the harmonisation process, the pendulum swing right across ... the GAMA manual was adopted in toto ... and the old DCA style charts were thrown out with the baby and the bathwater ...
(c) Among other things, the Australian charts used the same distance factors across all aircraft types
Sort of correct .. the use of these charts generally applied to the ANO 101.22 aircraft (lighties)
(d) This is where those graphs of declared conditions came in.
Bit off the mark here, I'm afraid. If we go back a long way, Australia was responsible for PNG and, given the poor performance capability of the earlier piston aircraft and the significant terrain in PNG, there arose a classification known as Developmental Air Services. (These predated my time and, while they would have been applicable to mainland activities, my understanding was that the driver was PNG operations). As far as I can see, apart from a legacy definition which somehow hasn't been culled from the CAO, DAS have gone the way of the dodo. Declared conditions were associated with these older operational standards.
(e) .. and you may use the manufacturers performance charts.
.. but do so with considerable circumspection .. presume that the POH data is barely achievable.
Moderator
Previous post edited to correct a temporary brain f@rt problem on my part .. the GAMA Ops Manual document predated the ICAO and the documentation citations are now included if anyone is interested.
Edited by Tail Wheel
Edited by Tail Wheel
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Interesting jt... the old P-charts were still in use in NZ until relatively recently, with nothing really significant provided since to replicate the calculations they provided. To my way of thinking, they should be able to be reproduced electronically -if the calculations/factors used in producing the charts are still available/published somewhere... and quite a bit of time spent getting them sorted. From memory (I don't have an old P-chart to refer to) most of the factors should have been fairly linear... so fairly easy to reproduce. Others would require a bit of mathematics...
Any idea where I would be able to source the calculations used to generate the charts? And the fudge-factors too? I'm assuming the fudge-factors for most aircraft (light singles/twins) were fairly common across the board? Would the fudge factors have been used predominantly to allow for the differing skill-sets of various pilots likely to operate the airframe, weighted towards the lower end of the scale?
Any idea where I would be able to source the calculations used to generate the charts? And the fudge-factors too? I'm assuming the fudge-factors for most aircraft (light singles/twins) were fairly common across the board? Would the fudge factors have been used predominantly to allow for the differing skill-sets of various pilots likely to operate the airframe, weighted towards the lower end of the scale?
Moderator
Edited by Tail Wheel 
.. cheeky bugger !!
RadioSaigon,
they should be able to be reproduced electronically
Dead easy, the earlier calculation set was quite simple and you could set it up on a spreadsheet in five minutes, tops. However, I suggest that John F's memo be avoided as it is in a different league .. big equations ... and not really necessary for piston aeroplanes but pretty good for light turboprops.
if the calculations/factors used in producing the charts are still available/published somewhere
Internal DCA memo reports from a long time ago (head scratching here ... AF-43 ?) and you probably would have great trouble getting them from CASA due to all the staff changes and the fact that no-one uses them any more. I would guess that the only blokes in house who might have a copy of the old memo tucked away would be Nick C or Dave P.
However, apropos of nothing, I just happened to run across my file copies the other week so I'll dig the earlier memo out again during the next couple of weeks and post the basics for anyone who might be interested. The fudge factors came out of the old ANO (CAO) 101.22 which has long been consigned to the waste bin .. although chaps like me and DJPil still have copies tucked away in the bottom drawer of the filing cabinet somewhere ...
Would the fudge factors have been used predominantly to allow for the differing skill-sets of various pilots likely to operate the airframe, weighted towards the lower end of the scale?
Not really ... In the flight test side of things, we toss out "bad" results, even if we just don't like the way that that run went ... and then the aerodynamicist who analyses the stuff does likewise .... so the final dataset tends to be a bit on the optimistic side of things.
The aim is to have realistic factors incorporated into the published results so that there is a margin for the real world and the average pilot punter on the one hand .. but not so much of a margin that the numbers are held up to ridicule as being unrealistic and are ignored by the folk whom they are intended to help in day to day operations.
.. cheeky bugger !!
RadioSaigon,
they should be able to be reproduced electronically
Dead easy, the earlier calculation set was quite simple and you could set it up on a spreadsheet in five minutes, tops. However, I suggest that John F's memo be avoided as it is in a different league .. big equations ... and not really necessary for piston aeroplanes but pretty good for light turboprops.
if the calculations/factors used in producing the charts are still available/published somewhere
Internal DCA memo reports from a long time ago (head scratching here ... AF-43 ?) and you probably would have great trouble getting them from CASA due to all the staff changes and the fact that no-one uses them any more. I would guess that the only blokes in house who might have a copy of the old memo tucked away would be Nick C or Dave P.
However, apropos of nothing, I just happened to run across my file copies the other week so I'll dig the earlier memo out again during the next couple of weeks and post the basics for anyone who might be interested. The fudge factors came out of the old ANO (CAO) 101.22 which has long been consigned to the waste bin .. although chaps like me and DJPil still have copies tucked away in the bottom drawer of the filing cabinet somewhere ...
Would the fudge factors have been used predominantly to allow for the differing skill-sets of various pilots likely to operate the airframe, weighted towards the lower end of the scale?
Not really ... In the flight test side of things, we toss out "bad" results, even if we just don't like the way that that run went ... and then the aerodynamicist who analyses the stuff does likewise .... so the final dataset tends to be a bit on the optimistic side of things.
The aim is to have realistic factors incorporated into the published results so that there is a margin for the real world and the average pilot punter on the one hand .. but not so much of a margin that the numbers are held up to ridicule as being unrealistic and are ignored by the folk whom they are intended to help in day to day operations.
