How to classify "new advanced aircraft"
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How to classify "new advanced aircraft"
I am working with a group involved in the development of criteria for instrument procedures. Manufacturers and operators have been asking for the current design criteria to be updated to reflect the capabilities of modern “Advanced transport aircraft”.
This class of aircraft might benefit from smaller lateral and vertical approach volumes for precision approaches, but should certainly benefit from reduced height loss values. The current PANS-OPS criteria is based on a errors relating to direct drive altimeters (1968 Report of the UK All Weather Operations Committee). The hysteresis of these is claimed to be eliminated with modern piezoelectric sensors. Just this improvement alone would reduce OCA/H values by 9m.
The problem is how best to identify this class of "advanced" aircraft. So far four possible definitions have been suggested:
1) RVSM approved aircraft – these aircraft must have modern altimeter systems. Unfortunately the altimeter specification is geared to performance above 29000 ft and is not expressed in a way that is easily translated into mean and standard deviation values at normal instrument procedure altitudes.
2) RNP approved aircraft – unfortunately the standard RNP criteria deals only with lateral performance and even 0.1 RNP is large compared with current precision approach criteria. The upcoming RNP/AR (ICAO version of the FAA-SAAAR criteria) does contain a more stringent altimeter error requirement. However, the rather extensive aircraft and operational approval requirements mean that the number of approved operators is likely to be small.
3) Aircraft first certificated after 1982. Various sources have suggested that all such aircraft would have improved altimeter systems (at least for Part 121 aircraft).
4) Aircraft equipped with dual digital ADCs.
If anyone has comments or alternative suggestions, now is the time such advice would be very useful.
As a postcript, you may not know that the current height loss values come from a dynamic model devised by W.J.G. Pinsker of Aero Flight, RAE Bedford. Unfortunately he never explained how he derived the model - it came to us as a graphical solution which was implemeted in a monte-carlo FORTRAN program. It is only this year that we have obtained the full theoretical explanation, plus an update. This came from Dr. Radislav Danilov, of the Russian aircraft certification authority. It transpired that he had written his doctorial thesis on Pinsker's model some 20 years ago. Pinsker died in 1998, and you will be pleased to hear that his family are happy to know that his work continues to be remembered.
This class of aircraft might benefit from smaller lateral and vertical approach volumes for precision approaches, but should certainly benefit from reduced height loss values. The current PANS-OPS criteria is based on a errors relating to direct drive altimeters (1968 Report of the UK All Weather Operations Committee). The hysteresis of these is claimed to be eliminated with modern piezoelectric sensors. Just this improvement alone would reduce OCA/H values by 9m.
The problem is how best to identify this class of "advanced" aircraft. So far four possible definitions have been suggested:
1) RVSM approved aircraft – these aircraft must have modern altimeter systems. Unfortunately the altimeter specification is geared to performance above 29000 ft and is not expressed in a way that is easily translated into mean and standard deviation values at normal instrument procedure altitudes.
2) RNP approved aircraft – unfortunately the standard RNP criteria deals only with lateral performance and even 0.1 RNP is large compared with current precision approach criteria. The upcoming RNP/AR (ICAO version of the FAA-SAAAR criteria) does contain a more stringent altimeter error requirement. However, the rather extensive aircraft and operational approval requirements mean that the number of approved operators is likely to be small.
3) Aircraft first certificated after 1982. Various sources have suggested that all such aircraft would have improved altimeter systems (at least for Part 121 aircraft).
4) Aircraft equipped with dual digital ADCs.
If anyone has comments or alternative suggestions, now is the time such advice would be very useful.
As a postcript, you may not know that the current height loss values come from a dynamic model devised by W.J.G. Pinsker of Aero Flight, RAE Bedford. Unfortunately he never explained how he derived the model - it came to us as a graphical solution which was implemeted in a monte-carlo FORTRAN program. It is only this year that we have obtained the full theoretical explanation, plus an update. This came from Dr. Radislav Danilov, of the Russian aircraft certification authority. It transpired that he had written his doctorial thesis on Pinsker's model some 20 years ago. Pinsker died in 1998, and you will be pleased to hear that his family are happy to know that his work continues to be remembered.
Joined: Apr 2002
Posts: 734
Likes: 0
From: Nirvana South
Robert,
Further thought is that is predicating an approach on a barometric altimeter or ADC still valid? (Despite what Nav Canada would like us to beleive about Temperature Compensation). The majority of current Part 121 & 135 aircraft are going to use a radio altimeter below 2500 feet agl and, if an ILS is available, use a Decision Height (aka RADIO) not the BARO Minimum Descent Altitude.
Future aircraft with Wide Area Augementation System (WAAS) GPS will also not use a baro altimeter but derive it from the GPS for an LPV approach again with a Decision Height lower than the equivalent MDA.
BTW just talked to one of our vendors' engineers who's been flight testing their first WAAS-capable GPS. He said the most remarkable thing both he & the crew noticed was the absence of dither in position - their aircraft had a chart display with an own aircraft symbol and it was rock steady not the usual slight random movement.
Further thought is that is predicating an approach on a barometric altimeter or ADC still valid? (Despite what Nav Canada would like us to beleive about Temperature Compensation). The majority of current Part 121 & 135 aircraft are going to use a radio altimeter below 2500 feet agl and, if an ILS is available, use a Decision Height (aka RADIO) not the BARO Minimum Descent Altitude.
Future aircraft with Wide Area Augementation System (WAAS) GPS will also not use a baro altimeter but derive it from the GPS for an LPV approach again with a Decision Height lower than the equivalent MDA.
BTW just talked to one of our vendors' engineers who's been flight testing their first WAAS-capable GPS. He said the most remarkable thing both he & the crew noticed was the absence of dither in position - their aircraft had a chart display with an own aircraft symbol and it was rock steady not the usual slight random movement.
Joined: Dec 2002
Posts: 2,774
Likes: 350
From: UK
Robert,
I was privileged to have met Dr Pinsker on several occasions where we discussed the differences between open and closed loop landing flare manoeuvres, and thence go-around manoeuvres. He also introduced me to the idea of lift energy, where the wing generates the energy and the tailplane distributes it. Thus, by using more ‘up’ elevator during a go-around, providing more ‘up’ energy, there is less height loss etc, etc.
I flew many of his test points exploring height loss during go-around, these were mainly from 50 ft in support of the Economic Cat 3 Programme at Bedford. I suspect that the ht loss formula used in JAR AWO stemmed from this work, but it may only be relevant to rad alt operations. I think that ground effect was also considered.
There is an example of achieving a new system ‘sub-classification’ in JAR-OPS 1 (sub part E) with the ‘super fail-passive’ autopilot, where an approved system can benefit from lower visibility minima providing operational procedures are modified – GA for any failure. However the method for this approval requires operational demonstration of ‘a highly reliable system’ in service, and only applies to the automatic components of the AWO system. The piloting aspects were covered by existing GA training from 50 ft – no change.
I assume that the benefits sought from the use of modern altimetry would only apply to Cat 1 or NPA approaches.
Where a pressure source is to be used perhaps the largest altitude error will come from the accuracy in setting the datum, which depends on the human’s ability or ‘desire’ (human factors) for accuracy. Geometric altitude (GPS) should not have this problem, but I do not have sufficient details to speculate further. It might be easier to envisage the certification of GPS altitude in the new role if it were already in common use for all altitude tasks. I note that there are quantified reports of significant GPS altitude errors due to external electronic interference.
The current problem of GA altitude loss from MDA (or just above) has been well researched. And even though in some instances a GA from MDA infringes current safety margins (PANS-OPS / TERPS differ) many regulators judge that the benefits of a stabilised, continuous descent with GA at MDA vastly outway the hazards of a ‘dive and drive’ procedure. Thus the benefits (improved safety) come from viewing the overall operation, consisting of the regulations (‘system’ safety), and the operational flight aspects (crew human factors). Such an approach might be required for the altimeter / GA ht loss proposals.
I would be concerned if the arguments for a revision crept into changing more than the altitude component (OCH/A) i.e. “we can go lower, we will be closer, thus we can reduce the visibility”. As with many weather related operations there are few such direct relationships and it should be noted that the ‘transformational’ weather conditions (Cat 2, Cat 1, and NPA instrument to visual transition) often result in situations that require a GA or in which, having made a decision to land, it can subsequently be incorrect.
There are several examples of such regulatory creep i.e. use of certified HUD landing minima for take-off, but the HUD symbols did not enable safe flight with an engine failure during take-off; an engine failed GA was assumed to be a non HUD instrument task (lateral accelerometer). There are similar debates about lowering Cat 2 visibility minima with the removal of the 80% autopilot coupled rule, but the auto / manual flight aspects in this instance are not related.
Dr Sidney Dekker has written an interesting paper on the problem of small changes, gaps, or assumptions made in regulatory methods, see Past the edge of chaos.
A quote from his paper would be good guidance for any regulator, design team, or test pilot:-
“The most important ingredient of engineering a resilient system is constantly testing whether ideas about risk still match with reality; whether the model of operations (and what makes them safe or unsafe) is still up to date. Helios 522 may suggest that we, in Europe, may still be applying models that no longer are.”
I was privileged to have met Dr Pinsker on several occasions where we discussed the differences between open and closed loop landing flare manoeuvres, and thence go-around manoeuvres. He also introduced me to the idea of lift energy, where the wing generates the energy and the tailplane distributes it. Thus, by using more ‘up’ elevator during a go-around, providing more ‘up’ energy, there is less height loss etc, etc.
I flew many of his test points exploring height loss during go-around, these were mainly from 50 ft in support of the Economic Cat 3 Programme at Bedford. I suspect that the ht loss formula used in JAR AWO stemmed from this work, but it may only be relevant to rad alt operations. I think that ground effect was also considered.
There is an example of achieving a new system ‘sub-classification’ in JAR-OPS 1 (sub part E) with the ‘super fail-passive’ autopilot, where an approved system can benefit from lower visibility minima providing operational procedures are modified – GA for any failure. However the method for this approval requires operational demonstration of ‘a highly reliable system’ in service, and only applies to the automatic components of the AWO system. The piloting aspects were covered by existing GA training from 50 ft – no change.
I assume that the benefits sought from the use of modern altimetry would only apply to Cat 1 or NPA approaches.
Where a pressure source is to be used perhaps the largest altitude error will come from the accuracy in setting the datum, which depends on the human’s ability or ‘desire’ (human factors) for accuracy. Geometric altitude (GPS) should not have this problem, but I do not have sufficient details to speculate further. It might be easier to envisage the certification of GPS altitude in the new role if it were already in common use for all altitude tasks. I note that there are quantified reports of significant GPS altitude errors due to external electronic interference.
The current problem of GA altitude loss from MDA (or just above) has been well researched. And even though in some instances a GA from MDA infringes current safety margins (PANS-OPS / TERPS differ) many regulators judge that the benefits of a stabilised, continuous descent with GA at MDA vastly outway the hazards of a ‘dive and drive’ procedure. Thus the benefits (improved safety) come from viewing the overall operation, consisting of the regulations (‘system’ safety), and the operational flight aspects (crew human factors). Such an approach might be required for the altimeter / GA ht loss proposals.
I would be concerned if the arguments for a revision crept into changing more than the altitude component (OCH/A) i.e. “we can go lower, we will be closer, thus we can reduce the visibility”. As with many weather related operations there are few such direct relationships and it should be noted that the ‘transformational’ weather conditions (Cat 2, Cat 1, and NPA instrument to visual transition) often result in situations that require a GA or in which, having made a decision to land, it can subsequently be incorrect.
There are several examples of such regulatory creep i.e. use of certified HUD landing minima for take-off, but the HUD symbols did not enable safe flight with an engine failure during take-off; an engine failed GA was assumed to be a non HUD instrument task (lateral accelerometer). There are similar debates about lowering Cat 2 visibility minima with the removal of the 80% autopilot coupled rule, but the auto / manual flight aspects in this instance are not related.
Dr Sidney Dekker has written an interesting paper on the problem of small changes, gaps, or assumptions made in regulatory methods, see Past the edge of chaos.
A quote from his paper would be good guidance for any regulator, design team, or test pilot:-
“The most important ingredient of engineering a resilient system is constantly testing whether ideas about risk still match with reality; whether the model of operations (and what makes them safe or unsafe) is still up to date. Helios 522 may suggest that we, in Europe, may still be applying models that no longer are.”
Guest
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"Further thought is that is predicating an approach on a barometric altimeter or ADC still valid? (Despite what Nav Canada would like us to beleive about Temperature Compensation). "
We are looking at normal Cat I ILS here, and the height loss values are those in ICAO PANS-OPS (Doc 8168) - NOT the FAA TERPS criteria. Better believe the temerature correction advised by Transport Canada, since they are supported by some very real evidence. Peter Foreman's (IFALPA) report of his discussion with a South American operator who lnaded before him and had a GPWS warning on a very cold day for one, and Don Batgeman's world tour in their instrumented King Air (one UK airport had an 800 ft error). Don Bateman is the engineer who invented the GPWS system. The error is based on the Off Standard atmosphere as defined by the Engneering Sciences Data Unit - it is the standard lapse rate shifted to the required colder temperature. It is recognized that the real lapse rate is often very different (inversions etc), but at least it will prevent some of the CFIT accidents!
"The majority of current Part 121 & 135 aircraft are going to use a radio altimeter below 2500 feet agl and, if an ILS is available, use a Decision Height (aka RADIO) not the BARO Minimum Descent Altitude."
You alarm me a little - For Cat II operations OK, and a radio altimeter OCA/H is normally promulgated. However, for Cat I it is an option but seldom promulgated, while for non-precision, never.
"Future aircraft with Wide Area Augementation System (WAAS) GPS will also not use a baro altimeter but derive it from the GPS for an LPV approach again with a Decision Height lower than the equivalent MDA."
Be sure you know just what is b eing promulgated - there are sites where the terrain in the approach is not suitable for radio altimeters!
Many thanks for your input, so far the best suggestion is the RVSM spec since it willcover those older aircraft that have the modern peizoelectric altimeters.
Robert
We are looking at normal Cat I ILS here, and the height loss values are those in ICAO PANS-OPS (Doc 8168) - NOT the FAA TERPS criteria. Better believe the temerature correction advised by Transport Canada, since they are supported by some very real evidence. Peter Foreman's (IFALPA) report of his discussion with a South American operator who lnaded before him and had a GPWS warning on a very cold day for one, and Don Batgeman's world tour in their instrumented King Air (one UK airport had an 800 ft error). Don Bateman is the engineer who invented the GPWS system. The error is based on the Off Standard atmosphere as defined by the Engneering Sciences Data Unit - it is the standard lapse rate shifted to the required colder temperature. It is recognized that the real lapse rate is often very different (inversions etc), but at least it will prevent some of the CFIT accidents!
"The majority of current Part 121 & 135 aircraft are going to use a radio altimeter below 2500 feet agl and, if an ILS is available, use a Decision Height (aka RADIO) not the BARO Minimum Descent Altitude."
You alarm me a little - For Cat II operations OK, and a radio altimeter OCA/H is normally promulgated. However, for Cat I it is an option but seldom promulgated, while for non-precision, never.
"Future aircraft with Wide Area Augementation System (WAAS) GPS will also not use a baro altimeter but derive it from the GPS for an LPV approach again with a Decision Height lower than the equivalent MDA."
Be sure you know just what is b eing promulgated - there are sites where the terrain in the approach is not suitable for radio altimeters!
Many thanks for your input, so far the best suggestion is the RVSM spec since it willcover those older aircraft that have the modern peizoelectric altimeters.
Robert
Guest
Posts: n/a
Many thanks for your response.
"I flew many of his test points exploring height loss during go-around, these were mainly from 50 ft in support of the Economic Cat 3 Programme at Bedford. I suspect that the ht loss formula used in JAR AWO stemmed from this work, but it may only be relevant to rad alt operations. I think that ground effect was also considered."
I think we must have have met in another incarnation - I was at BLEU 1965-68, but I think before the economic Cat II (or was it III) was going on. I left the RAF in 1970 and joined what was then the Board of Trade, where we asked RAE Farnborough to develop a software to predict height loss and also asked Pinsker to be the technical adviser. After a month he sent me a couple of graphs and a note saying he would rather do it himself instead of watching someone else screw it up! Those graphs predicted height loss and time to lowest point for one combinations of vertical rate, applied g, period of SPO and damping in pitch. RAE Farnborough wrote a Monte Carlo program based on his graphs and flight test data on distributions of vertical rate and g (plus a correlation of 0.5 between vertical rate and g. The altimeter error was based on the 1968 report of the UK All Weather Operations Committee. Unfortunately this was sent to the Public Records Office and I have had no success at all in getting them to respond to requests for retrieval. It gave means and variances for the component errors for direct dreive, servo and corercted servo altimeters. However I want to update these and cannot find an expert who can take the RVSM spec and deduce the equivalent errors for modern peizoelectric altimeters. If you know of one we would be delighted.
"There is an example of achieving a new system ‘sub-classification’ in JAR-OPS 1 (sub part E) with the ‘super fail-passive’ autopilot... However the method for this approval requires operational demonstration of ‘a highly reliable system’ in service..."
This was the approach the FAA used in the SAAAR criteria (which I have been assisting in converting into the equivalent ICAO criteria for RNP/AR). They defined a quadratic equation and obtained confirmation from aircraft manufactueres that their aircraft systems could meet it. They then published this in the new ICAO Performance Based Navigation Manual as an aircraft approval requirement. Since this is yet to be published by ICAO I include it here:
-8.8*10E-8*(Elevation)^2 + 6.5*10E-3*(Elevation)+50
This is one option, but it will require operators to spend the money on getting the appropriate approval.
"I assume that the benefits sought from the use of modern altimetry would only apply to Cat 1 or NPA approaches. "
Correct.
"Where a pressure source is to be used perhaps the largest altitude error will come from the accuracy in setting the datum, which depends on the human’s ability or ‘desire’ (human factors) for accuracy."
You are of course corect, the setting error can be relatively large and is presumably a bias error - I do not think it was ever considered as a separate component in the SAAAR criteria. PANS-OPS Vol I does contain updated errors though the much smaller ATIS error was included in the SAAR criteria (20 ft).
"... I note that there are quantified reports of significant GPS altitude errors due to external electronic interference."
Would appreciate details if available. I have heard of the long term drift noted by the Eurocontrol RVSM monitoring but not these errors.
"... The current problem of GA altitude loss from MDA (or just above) has been well researched."
Unfortunately we are looking at extrapolating down to 10E-5 probability and that is always difficult from test data (there is never enough to obtain a sensible confidence level). Hence the need for the height loss model.
"... And even though in some instances a GA from MDA infringes current safety margins (PANS-OPS / TERPS differ)..."
We have been having an interesting debate over the TERPS vs PANS-OPS missed approach. The problem with TERPS is the large reduction in horizontal distance between initiation and SOC if the missed approach gradient is increased. The new ICAO RNP/AR criteria is thus based on the PANS-OPS concept, not TERPS.
"... many regulators judge that the benefits of a stabilised, continuous descent with GA at MDA vastly outway the hazards of a ‘dive and drive’ procedure. Thus the benefits (improved safety) come from viewing the overall operation, consisting of the regulations (‘system’ safety), and the operational flight aspects (crew human factors). Such an approach might be required for the altimeter / GA ht loss proposals."
My friend Theo van der Ven at KLM (Adviser to the IATA Member of the ICAO Obstacle Clearance Panel), also member of the TARA group and others, has been pressing this for the last three Panel meetings. He is faced with opposition from those Members who regard MDA as a never go below height. We are still working on this one.
"... I would be concerned if the arguments for a revision crept into changing more than the altitude component (OCH/A) i.e. “we can go lower, we will be closer, thus we can reduce the visibility”. As with many weather related operations there are few such direct relationships and it should be noted that the ‘transformational’ weather conditions (Cat 2, Cat 1, and NPA instrument to visual transition) often result in situations that require a GA or in which, having made a decision to land, it can subsequently be incorrect."
Thisis an interesting point of view. However, from the procedure design aspect, the end product is an OCA/H that will ensure clearance from obstacles at the desired level of probability (for ILS/MLS/GBAS). The DA/H and RVR associated with the OCA/H are operational matters. Hence the problem is one for JAR-OPS (or its Euro successor).
"... Dr Sidney Dekker has written an interesting paper on the problem of small changes, gaps, or assumptions made in regulatory methods, see Past the edge of chaos. A quote from his paper would be good guidance for any regulator, design team, or test pilot:-
“The most important ingredient of engineering a resilient system is constantly testing whether ideas about risk still match with reality; whether the model of operations (and what makes them safe or unsafe) is still up to date. Helios 522 may suggest that we, in Europe, may still be applying models that no longer are."
Precisely -that is why we are under pressure from manufacturers to update the PANS-OPS criteria to account for "Advanced aircraft and systems" - hence this request for help in finding a definition for same!!!
Many thanks for your input, and interested in any further info.
Robert
"I flew many of his test points exploring height loss during go-around, these were mainly from 50 ft in support of the Economic Cat 3 Programme at Bedford. I suspect that the ht loss formula used in JAR AWO stemmed from this work, but it may only be relevant to rad alt operations. I think that ground effect was also considered."
I think we must have have met in another incarnation - I was at BLEU 1965-68, but I think before the economic Cat II (or was it III) was going on. I left the RAF in 1970 and joined what was then the Board of Trade, where we asked RAE Farnborough to develop a software to predict height loss and also asked Pinsker to be the technical adviser. After a month he sent me a couple of graphs and a note saying he would rather do it himself instead of watching someone else screw it up! Those graphs predicted height loss and time to lowest point for one combinations of vertical rate, applied g, period of SPO and damping in pitch. RAE Farnborough wrote a Monte Carlo program based on his graphs and flight test data on distributions of vertical rate and g (plus a correlation of 0.5 between vertical rate and g. The altimeter error was based on the 1968 report of the UK All Weather Operations Committee. Unfortunately this was sent to the Public Records Office and I have had no success at all in getting them to respond to requests for retrieval. It gave means and variances for the component errors for direct dreive, servo and corercted servo altimeters. However I want to update these and cannot find an expert who can take the RVSM spec and deduce the equivalent errors for modern peizoelectric altimeters. If you know of one we would be delighted.
"There is an example of achieving a new system ‘sub-classification’ in JAR-OPS 1 (sub part E) with the ‘super fail-passive’ autopilot... However the method for this approval requires operational demonstration of ‘a highly reliable system’ in service..."
This was the approach the FAA used in the SAAAR criteria (which I have been assisting in converting into the equivalent ICAO criteria for RNP/AR). They defined a quadratic equation and obtained confirmation from aircraft manufactueres that their aircraft systems could meet it. They then published this in the new ICAO Performance Based Navigation Manual as an aircraft approval requirement. Since this is yet to be published by ICAO I include it here:
-8.8*10E-8*(Elevation)^2 + 6.5*10E-3*(Elevation)+50
This is one option, but it will require operators to spend the money on getting the appropriate approval.
"I assume that the benefits sought from the use of modern altimetry would only apply to Cat 1 or NPA approaches. "
Correct.
"Where a pressure source is to be used perhaps the largest altitude error will come from the accuracy in setting the datum, which depends on the human’s ability or ‘desire’ (human factors) for accuracy."
You are of course corect, the setting error can be relatively large and is presumably a bias error - I do not think it was ever considered as a separate component in the SAAAR criteria. PANS-OPS Vol I does contain updated errors though the much smaller ATIS error was included in the SAAR criteria (20 ft).
"... I note that there are quantified reports of significant GPS altitude errors due to external electronic interference."
Would appreciate details if available. I have heard of the long term drift noted by the Eurocontrol RVSM monitoring but not these errors.
"... The current problem of GA altitude loss from MDA (or just above) has been well researched."
Unfortunately we are looking at extrapolating down to 10E-5 probability and that is always difficult from test data (there is never enough to obtain a sensible confidence level). Hence the need for the height loss model.
"... And even though in some instances a GA from MDA infringes current safety margins (PANS-OPS / TERPS differ)..."
We have been having an interesting debate over the TERPS vs PANS-OPS missed approach. The problem with TERPS is the large reduction in horizontal distance between initiation and SOC if the missed approach gradient is increased. The new ICAO RNP/AR criteria is thus based on the PANS-OPS concept, not TERPS.
"... many regulators judge that the benefits of a stabilised, continuous descent with GA at MDA vastly outway the hazards of a ‘dive and drive’ procedure. Thus the benefits (improved safety) come from viewing the overall operation, consisting of the regulations (‘system’ safety), and the operational flight aspects (crew human factors). Such an approach might be required for the altimeter / GA ht loss proposals."
My friend Theo van der Ven at KLM (Adviser to the IATA Member of the ICAO Obstacle Clearance Panel), also member of the TARA group and others, has been pressing this for the last three Panel meetings. He is faced with opposition from those Members who regard MDA as a never go below height. We are still working on this one.
"... I would be concerned if the arguments for a revision crept into changing more than the altitude component (OCH/A) i.e. “we can go lower, we will be closer, thus we can reduce the visibility”. As with many weather related operations there are few such direct relationships and it should be noted that the ‘transformational’ weather conditions (Cat 2, Cat 1, and NPA instrument to visual transition) often result in situations that require a GA or in which, having made a decision to land, it can subsequently be incorrect."
Thisis an interesting point of view. However, from the procedure design aspect, the end product is an OCA/H that will ensure clearance from obstacles at the desired level of probability (for ILS/MLS/GBAS). The DA/H and RVR associated with the OCA/H are operational matters. Hence the problem is one for JAR-OPS (or its Euro successor).
"... Dr Sidney Dekker has written an interesting paper on the problem of small changes, gaps, or assumptions made in regulatory methods, see Past the edge of chaos. A quote from his paper would be good guidance for any regulator, design team, or test pilot:-
“The most important ingredient of engineering a resilient system is constantly testing whether ideas about risk still match with reality; whether the model of operations (and what makes them safe or unsafe) is still up to date. Helios 522 may suggest that we, in Europe, may still be applying models that no longer are."
Precisely -that is why we are under pressure from manufacturers to update the PANS-OPS criteria to account for "Advanced aircraft and systems" - hence this request for help in finding a definition for same!!!
Many thanks for your input, and interested in any further info.
Robert
Joined: Dec 2002
Posts: 2,774
Likes: 350
From: UK
Robert, re GPS geometric altitude errors you should contact Don Bateman.
We probably met during the reporting phase of the ECIII program – to CAA and Gov. The final ECIII report provides examples of risk boundaries re ground contact during go around, but only from 50ft.
At that time (1979) and subsequently, the UK CAA used a fog model which I believe supplemented ECAC doc 17 to approve operating minima dependant on aircraft type. Although complex, the model appeared to provide a very realistic first point of contact and good visual segment information. Again I believe that the model may have had a height loss component; or perhaps it only modelled the basic equation similar to the one which you have.
For a cross section of incidents that might have involved altimetry – failure to set QNH; see Celebrating TAWS ‘Saves’: But lessons still to be learnt.
My continuing investigation into these types of incidents suggests that QNH error, or failure to reset the altimeter, is still a very common error. Although not directly relevant to your question, the problem is related to modern aircraft systems particularly where QNH is used as the datum for VNAV approach waypoints (the majority of cases). Thus, just one small crew setting-error (or failure to cross check), it can affect both main altimeters and the NPA vertical navigation, which may have a visually powerful visual display providing the crew with even greater false confidence in their geometric position. Geometric altitude would provide a useful alerting system for such errors, even if it may not be sufficiently robust for primary use.
We probably met during the reporting phase of the ECIII program – to CAA and Gov. The final ECIII report provides examples of risk boundaries re ground contact during go around, but only from 50ft.
At that time (1979) and subsequently, the UK CAA used a fog model which I believe supplemented ECAC doc 17 to approve operating minima dependant on aircraft type. Although complex, the model appeared to provide a very realistic first point of contact and good visual segment information. Again I believe that the model may have had a height loss component; or perhaps it only modelled the basic equation similar to the one which you have.
For a cross section of incidents that might have involved altimetry – failure to set QNH; see Celebrating TAWS ‘Saves’: But lessons still to be learnt.
My continuing investigation into these types of incidents suggests that QNH error, or failure to reset the altimeter, is still a very common error. Although not directly relevant to your question, the problem is related to modern aircraft systems particularly where QNH is used as the datum for VNAV approach waypoints (the majority of cases). Thus, just one small crew setting-error (or failure to cross check), it can affect both main altimeters and the NPA vertical navigation, which may have a visually powerful visual display providing the crew with even greater false confidence in their geometric position. Geometric altitude would provide a useful alerting system for such errors, even if it may not be sufficiently robust for primary use.
Guest
Posts: n/a
Safetypee, How right you are:
"... incidents that might have involved altimetry – failure to set QNH"
On a separate issue I am interested in these because I have been involved in a number of aeronautical studies under the provisions of Annex 14 (penetrations of certain obstacle limitation surfaces can be permitted following an aeronautical study). There is no gudiance material at all in ICAO documents - just a basic concept that regularity and safety are to be considered. The regularity is simple - just check the effect on all the OCA/H for the aerodrome (including the various clearance angles for VOR, ASR and RSR etc).
The safety is the big problem. Allow one penetration and it is hard to reject the next, the end result a growing forest of obstacles penetrating the Annex 14 surfaces. I have now concluded that the airspace between the PANS-OPS obstacle clearance surfaces and the Annex 14 obstacle limitation surfaces is the only thing that protects the non-normal operation. Bear in mind that PANS-OPS specifically states it is for normal operations only.
This was brought home to me when contractors started asking for the maximum elevation instead of a specific height. The State had introduced a slum clearance scheme whereby constructors could level the slums around the airport and re-house the tennants in new apartment blocks - the profit lay in an equivalent number of apartments the could sell on the private market. I have since recommended against all subsequent requests pending the State establishing some criteria to limit these constructions (this is a State respibsibility, not mine!). There is now a backlog of 120 applications!
Hence I was very interested in the type of non-normal accident you mentioned. I believe there was one at East Midlands recently when a crew forgot to reset the altimeter and flew the approach 1000ft too low. Of course these are very infrequent - but this is balanced by the probable impact on the aerodrome operations of the public enquiry that usually follows an accident of that magnitude (think Schiphol and the 747 that hit an apartment block).
I identified this problem at a recent ICAO meeting, as a result of which I have to produce some proposals - your suggestion will be most useful. Thank you.
Robert
"... incidents that might have involved altimetry – failure to set QNH"
On a separate issue I am interested in these because I have been involved in a number of aeronautical studies under the provisions of Annex 14 (penetrations of certain obstacle limitation surfaces can be permitted following an aeronautical study). There is no gudiance material at all in ICAO documents - just a basic concept that regularity and safety are to be considered. The regularity is simple - just check the effect on all the OCA/H for the aerodrome (including the various clearance angles for VOR, ASR and RSR etc).
The safety is the big problem. Allow one penetration and it is hard to reject the next, the end result a growing forest of obstacles penetrating the Annex 14 surfaces. I have now concluded that the airspace between the PANS-OPS obstacle clearance surfaces and the Annex 14 obstacle limitation surfaces is the only thing that protects the non-normal operation. Bear in mind that PANS-OPS specifically states it is for normal operations only.
This was brought home to me when contractors started asking for the maximum elevation instead of a specific height. The State had introduced a slum clearance scheme whereby constructors could level the slums around the airport and re-house the tennants in new apartment blocks - the profit lay in an equivalent number of apartments the could sell on the private market. I have since recommended against all subsequent requests pending the State establishing some criteria to limit these constructions (this is a State respibsibility, not mine!). There is now a backlog of 120 applications!
Hence I was very interested in the type of non-normal accident you mentioned. I believe there was one at East Midlands recently when a crew forgot to reset the altimeter and flew the approach 1000ft too low. Of course these are very infrequent - but this is balanced by the probable impact on the aerodrome operations of the public enquiry that usually follows an accident of that magnitude (think Schiphol and the 747 that hit an apartment block).
I identified this problem at a recent ICAO meeting, as a result of which I have to produce some proposals - your suggestion will be most useful. Thank you.
Robert
Joined: Apr 2002
Posts: 734
Likes: 0
From: Nirvana South
Robert,
If the largest error comes from the baro correction on the ground, why not use all radio-based aids? My previous post just pointed out that all "new advanced aircraft" will have (at least) one radio altimeter and (at least) one GPS - soon to be updated if the GA market is anything to go by to WAAS-capable units that provide accurate altitudes above ground level irrespective of baro pressure measurement or temperature effects. I appreciate that the modern Air Data Computer also provides extremely accurate local pressure measurement but it is only as good as that taken at the ground and worse if there is any appreciable delay since that reading (& the temperature if cold) was taken & transmitted to the aircrew.
If the largest error comes from the baro correction on the ground, why not use all radio-based aids? My previous post just pointed out that all "new advanced aircraft" will have (at least) one radio altimeter and (at least) one GPS - soon to be updated if the GA market is anything to go by to WAAS-capable units that provide accurate altitudes above ground level irrespective of baro pressure measurement or temperature effects. I appreciate that the modern Air Data Computer also provides extremely accurate local pressure measurement but it is only as good as that taken at the ground and worse if there is any appreciable delay since that reading (& the temperature if cold) was taken & transmitted to the aircrew.
Guest
Posts: n/a
Dear ICT SLB,
The radio altimeter may be OK for the lower decision heights of Category II operations, but terrain profiles are not always suitable for the distance before the threshold applicable for Category I. It is an option in PANS-OPS for ILS/MLS and GBAS, but I do not know of any State which has provided it. Use for Cat I would require flight checks by the requestor and approval and I suppose the associated costs have been considered by the operators and rejected.
Regarding SBAS, the basic procedure design criteria specifies the use of the barometric altimeter, not the GNSS system, to establish decision height. Whilst GNSS is very accurate inthe horizontal plane, this is not the same in the vertical.
The radio altimeter may be OK for the lower decision heights of Category II operations, but terrain profiles are not always suitable for the distance before the threshold applicable for Category I. It is an option in PANS-OPS for ILS/MLS and GBAS, but I do not know of any State which has provided it. Use for Cat I would require flight checks by the requestor and approval and I suppose the associated costs have been considered by the operators and rejected.
Regarding SBAS, the basic procedure design criteria specifies the use of the barometric altimeter, not the GNSS system, to establish decision height. Whilst GNSS is very accurate inthe horizontal plane, this is not the same in the vertical.
Guest
Posts: n/a
New modern aircraft definitoin
Back again - still looking for a definition and also for updated altimeter specs. The current ones have not changed since the 1950s and the ECAC Working Group currently involved do not appear to be making much progress (difficulty getting consensus from manufacturers).
The pressure altimeter spec used in the Monte Carlo model inplementing the Pinsker solution is that given in the Board of Trade Report of the UK All Weather Operations Committee about 1968. Unfortunately this report was sent to the Public Records Office under the 30 year rule, and efforts to trace it have proved fruitless. If anyone knows where w can find a copy please let me know!
The RVSM criteria are not much help as it concentrates on errors at 40,000 ft., not on approach to land. We have also the FAA SAAAR altimeter error ASE equation (a quadratic with height as the variable), but that is no good as it was devised from data on one aircraft flown at max Mach number or IAS through a range of heights. Again, not quite the approach to land!
By the way, we never had any theoretical background on Pinsker's solution - only the two non-dimensionalised graphs. However, we now do have the ful background from Dr. Radislav Danilov from Russia, who wrote his PhD thesis on it many years ago. Jerry Robinson from Boeing fixed a contract to have him write it up and it should appear in the new Collision Risk Algorithm Manual from ICAO later this year. There will also be details of a validation made by Dr. Dave Staplelton using data from a KC10 program.
So - still looking for a definition for "new advance aircraft".
The pressure altimeter spec used in the Monte Carlo model inplementing the Pinsker solution is that given in the Board of Trade Report of the UK All Weather Operations Committee about 1968. Unfortunately this report was sent to the Public Records Office under the 30 year rule, and efforts to trace it have proved fruitless. If anyone knows where w can find a copy please let me know!
The RVSM criteria are not much help as it concentrates on errors at 40,000 ft., not on approach to land. We have also the FAA SAAAR altimeter error ASE equation (a quadratic with height as the variable), but that is no good as it was devised from data on one aircraft flown at max Mach number or IAS through a range of heights. Again, not quite the approach to land!
By the way, we never had any theoretical background on Pinsker's solution - only the two non-dimensionalised graphs. However, we now do have the ful background from Dr. Radislav Danilov from Russia, who wrote his PhD thesis on it many years ago. Jerry Robinson from Boeing fixed a contract to have him write it up and it should appear in the new Collision Risk Algorithm Manual from ICAO later this year. There will also be details of a validation made by Dr. Dave Staplelton using data from a KC10 program.
So - still looking for a definition for "new advance aircraft".
Joined: Dec 2001
Posts: 1,835
Likes: 3
From: Philadelphia PA
Robert:
Have you looked at how many times altimeter errors come in from human sources? Everything from mis-reported on the METAR report, to mis-transmitted to mis-heard to mis-set?
A Canadian friend of mine did a survey in Canada several years ago and found a shocking number of errors just in the METARs. He also found that even without WAAS, GPS height was as statistically accurate as barometric pressure.
Have you looked at how many times altimeter errors come in from human sources? Everything from mis-reported on the METAR report, to mis-transmitted to mis-heard to mis-set?
A Canadian friend of mine did a survey in Canada several years ago and found a shocking number of errors just in the METARs. He also found that even without WAAS, GPS height was as statistically accurate as barometric pressure.
Joined: Sep 2006
Posts: 2,181
Likes: 1
From: any town as retired.
Altimeter correction for cold ops
I would appreciate some guidance for the following typical winter ops in the USSR.!!!!
Gulfstream 550 operating into Estana: Temp -25c, pressure 1042, and almost sea level.
As an aside they were giving temp: fzra, 200mts rvr, and zero VV.
Cat 1 ILS, with say mins at 200ft.
Airport and aircraft CAT 2, but crew not current, and airport not declaring LVP.
All ops based on QNH, so no FMS complications.
What if any corrections should be added to the 200ft, for a) temperature, and b) pressure differences from ISA.
Many thanks, it was a cold Christmas there, as we managed to land, just on mins...(whatever they were!).
Temperature corrections are easy to locate and this was added, but I am concerned that there should also be a pressure difference correction.
glf
Gulfstream 550 operating into Estana: Temp -25c, pressure 1042, and almost sea level.
As an aside they were giving temp: fzra, 200mts rvr, and zero VV.
Cat 1 ILS, with say mins at 200ft.
Airport and aircraft CAT 2, but crew not current, and airport not declaring LVP.
All ops based on QNH, so no FMS complications.
What if any corrections should be added to the 200ft, for a) temperature, and b) pressure differences from ISA.
Many thanks, it was a cold Christmas there, as we managed to land, just on mins...(whatever they were!).
Temperature corrections are easy to locate and this was added, but I am concerned that there should also be a pressure difference correction.
glf
Joined: Dec 2002
Posts: 2,774
Likes: 350
From: UK
Robert, sorry to be a ‘killjoy’, but any definition of a ‘new advanced aircraft’ will be outdated by what ever comes next.
An attempt to provide a specific set of limits for separate classes of aircraft could result in a chaotic or confusing regulatory system. An example is with JAR-OPS 1 part H, where AWO limits attempt to cover most flight guidance systems ranging from autos, FDs, to HUD, intertwined with airborne and ground system integrity, and capped with lighting requirements. (and why do the crews require currency?). The resulting tables/matrices are a nightmare for most operators and the compromise minima generally the lower of previous national limits across Europe. One might question if this approach is conducive to improving safety.
An alternative approach might be to consider what the operators require – avoiding the outrageous requests for bigger, better, and more. We might conclude that the current regulatory system is good enough if the resulting capability was more widely available.
Operating capability has been limited by ground systems, thus the advent of the new airborne facilities.
Current operational limits are based on the inherent guidance accuracy-integrity (ground/air), flight technical error (what the aircraft can achieve), and altimetry. Staying with this concept then there is no need to change existing obstacle clearances / collision risk models providing that the overall system meets the current accuracy-integrity values. Thus conceptually a GPS/FMS could fly Cat3 anywhere provided that the altimetry requirements are met – fix the approach terrain; not forgetting that flt guidance systems might rely on accurate rad alt (flat approach). The operators / airports must bear some cost for the improvement in capability.
The major operating advantage would be at airports with nil/non precision approach that can be improved to Cat 1, which is probably all that is required / justified. Thus, providing that any new advanced aircraft system meets the current criteria there should be no objection to the operation.
One current pitfall is that some believe that the new systems improve the overall integrity of the operation, i.e. single GPS/WAAS for Cat 3. The danger in this is that the regulators might believe that is justified based on a relatively good Cat2/3 safety record.
We should heed the warning of the safety gurus who cite that the most dangerous time is during periods of change and the failure to listen to ‘history’.
An attempt to provide a specific set of limits for separate classes of aircraft could result in a chaotic or confusing regulatory system. An example is with JAR-OPS 1 part H, where AWO limits attempt to cover most flight guidance systems ranging from autos, FDs, to HUD, intertwined with airborne and ground system integrity, and capped with lighting requirements. (and why do the crews require currency?). The resulting tables/matrices are a nightmare for most operators and the compromise minima generally the lower of previous national limits across Europe. One might question if this approach is conducive to improving safety.
An alternative approach might be to consider what the operators require – avoiding the outrageous requests for bigger, better, and more. We might conclude that the current regulatory system is good enough if the resulting capability was more widely available.
Operating capability has been limited by ground systems, thus the advent of the new airborne facilities.
Current operational limits are based on the inherent guidance accuracy-integrity (ground/air), flight technical error (what the aircraft can achieve), and altimetry. Staying with this concept then there is no need to change existing obstacle clearances / collision risk models providing that the overall system meets the current accuracy-integrity values. Thus conceptually a GPS/FMS could fly Cat3 anywhere provided that the altimetry requirements are met – fix the approach terrain; not forgetting that flt guidance systems might rely on accurate rad alt (flat approach). The operators / airports must bear some cost for the improvement in capability.
The major operating advantage would be at airports with nil/non precision approach that can be improved to Cat 1, which is probably all that is required / justified. Thus, providing that any new advanced aircraft system meets the current criteria there should be no objection to the operation.
One current pitfall is that some believe that the new systems improve the overall integrity of the operation, i.e. single GPS/WAAS for Cat 3. The danger in this is that the regulators might believe that is justified based on a relatively good Cat2/3 safety record.
We should heed the warning of the safety gurus who cite that the most dangerous time is during periods of change and the failure to listen to ‘history’.
Per Ardua ad Astraeus
Joined: Mar 2000
Posts: 18,575
Likes: 4
From: UK
RW - it may not be of significance, but while I was flying for BA (pre-2004) they did publish (for 737) Radio DH's for CatI at certain airfields with the order that 'where published they should be used' so assuming the regulators were awake 
this must have been an 'approved' procedure.
this must have been an 'approved' procedure.
Joined: Feb 2005
Posts: 340
Likes: 1
From: KPHL
Robert,
As already mentioned, the time it takes to create this category and then certify aircraft within that category could be long enough that the specification may be outdated before it is used.
Rather than defining a new category that captures some of the improved precision now available, why don't you start at the beginning, determine a level of instrumentation performance that is required to reduce minima, reduce seperation, and/or increase traffic volume, and then define a category that meets those criteria?
For altimeter setting errors, I think most of those would be eliminated if the METAR was also transmitted digitally, and the aircraft announced if the aircraft altimeter settings differ from the one transmitted. Temperature correction errors could also be mitigated.
Height loss on overshoot is not something I've considered before. However, I have worked on height loss following engine failure with a second engine intentionally shut down. So many factors were involved that one solution wasn't possible, but applying a height to each factor was straight forward. Perhaps this approach would work for your specification. One aircraft might have excellent altimetry, but poor OEI climb performance. It may also be possible to apply reduced height loss based on procedures or training.
I have little else to add onthe content of the definition, but I would avoid the term "new advanced aircraft" and just focus on approach instrumentation performance.
Cheers,
Matthew.
As already mentioned, the time it takes to create this category and then certify aircraft within that category could be long enough that the specification may be outdated before it is used.
Rather than defining a new category that captures some of the improved precision now available, why don't you start at the beginning, determine a level of instrumentation performance that is required to reduce minima, reduce seperation, and/or increase traffic volume, and then define a category that meets those criteria?
For altimeter setting errors, I think most of those would be eliminated if the METAR was also transmitted digitally, and the aircraft announced if the aircraft altimeter settings differ from the one transmitted. Temperature correction errors could also be mitigated.
Height loss on overshoot is not something I've considered before. However, I have worked on height loss following engine failure with a second engine intentionally shut down. So many factors were involved that one solution wasn't possible, but applying a height to each factor was straight forward. Perhaps this approach would work for your specification. One aircraft might have excellent altimetry, but poor OEI climb performance. It may also be possible to apply reduced height loss based on procedures or training.
I have little else to add onthe content of the definition, but I would avoid the term "new advanced aircraft" and just focus on approach instrumentation performance.
Cheers,
Matthew.
