Category A and Performance Class 1
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Category A and Performance Class 1
This may have all been dealt with before.
Is there any readily available definitive regarding Category A definitions, certification and operations information and some info clarifying profiles and the concept of Performance Class 1.
Some pointers please.
Is there any readily available definitive regarding Category A definitions, certification and operations information and some info clarifying profiles and the concept of Performance Class 1.
Some pointers please.
Make yourself comfortable and try here for starters!
http://www.pprune.org/forums/showthr...light=hardcore
FNW
http://www.pprune.org/forums/showthr...light=hardcore
FNW
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Class 1 Cat A
Nick Lappos et al
The question I believe was more about what these subjects ARE rather than what one's opinion of their relevance is. Having recently been asked the same question by a customer I had to explain the reality of the situation rather than the academics of what it ought to be.
I have to say that what Nick says makes a lot of sense but as we all know our performance mantras have their origins in the fixed wing world and it is likely to be a while yet before we some common sense creeping into the world of helicopter performance.
What the standards posed by Cat A (Group A if you are a Brit) and Class 1 have done is forced the manufacturers to produce helicopters that are almost able to fly throughout the flight range on one engine. Irrespective of your thoughts about the applicability of 'Cat A' I reckon this is a 'good thing'. I recently saw a picture of Bo105 upside down in the 'oggin' in the GoM after it had suffered a single engine failure but been unable to maintain height at the weight he had elected (been forced to more like) operate at.
So - in the big debate about Cat A , is it a good thing or a bad thing - me, I plump for giving the guys a bit more to play with in an unforgiving and unpredictable world. save the Cat B stuff for the military.
Now I see that I haven't answered his question either and I'm not in the mood to write pages and pages about helicopter performance so I'll leave that to somebody else.
The question I believe was more about what these subjects ARE rather than what one's opinion of their relevance is. Having recently been asked the same question by a customer I had to explain the reality of the situation rather than the academics of what it ought to be.
I have to say that what Nick says makes a lot of sense but as we all know our performance mantras have their origins in the fixed wing world and it is likely to be a while yet before we some common sense creeping into the world of helicopter performance.
What the standards posed by Cat A (Group A if you are a Brit) and Class 1 have done is forced the manufacturers to produce helicopters that are almost able to fly throughout the flight range on one engine. Irrespective of your thoughts about the applicability of 'Cat A' I reckon this is a 'good thing'. I recently saw a picture of Bo105 upside down in the 'oggin' in the GoM after it had suffered a single engine failure but been unable to maintain height at the weight he had elected (been forced to more like) operate at.
So - in the big debate about Cat A , is it a good thing or a bad thing - me, I plump for giving the guys a bit more to play with in an unforgiving and unpredictable world. save the Cat B stuff for the military.
Now I see that I haven't answered his question either and I'm not in the mood to write pages and pages about helicopter performance so I'll leave that to somebody else.
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BHAB
Take a wander over to the BHAB site at http://www.bhab.flyer.co.uk/sitenew.htm
A little bit from that site.
"Group A/Class 1 helicopters, on take off or landing, are required, in the event of failure of a power unit, to be capable of rejecting safely onto the take off/landing area available or of flying away on the remaining power unit(s) avoiding all obstacles by a vertical margin of 35 feet."
A little bit from that site.
"Group A/Class 1 helicopters, on take off or landing, are required, in the event of failure of a power unit, to be capable of rejecting safely onto the take off/landing area available or of flying away on the remaining power unit(s) avoiding all obstacles by a vertical margin of 35 feet."
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canthover
I agree with FloaterNorthWest; take the trip to the thread he has indicated and then, if you have any further questions pose them, I'm sure they will be answered.
Definitions - both FAA and JAA are on the first page.
I agree with FloaterNorthWest; take the trip to the thread he has indicated and then, if you have any further questions pose them, I'm sure they will be answered.
Definitions - both FAA and JAA are on the first page.
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Does this help?
Helicopters are certified in one of several groups. For example, JAR classifications are 1, 2 and 3, which are broadly equivalent to the UK Groups A, A(Restricted) and B (see the table below).
These are different from Airworthiness Groups, which dictate how well the airframe stands up to a forced landing. In other words, the terms Category A and Category B (as opposed to Group A or B, or Class 1 or 2) are for certification purposes:
Passengers JAR Class UK AN(G)R
Over 19 1 A
9-19 2 A (Restricted)*
Less than 9 3 B**
Category A means multi-engined helicopters with engine and system isolation as per JAR-27/29, and Flight Manual performance based on a critical engine failure concept providing adequate surface area and performance capability for continued safe flight if an engine fails. In other words, in addition to making sure you have power available (by restricting MAUW) it provides space for rejected takeoffs and landings, and obstacle clearance.
Category B means single- or multi-engined helicopters not fully meeting Category A. They are not guaranteed to stay airborne if an engine fails and an unscheduled landing is assumed, possibly with some damage.
Category A helicopters may operate in Performance Class 1, 2 or 3, but Category B machines may only be operated under Class 3.
JAR Class 1 (Group A) helicopters offer the highest protection for passengers and require no forced landing provisions if the critical power unit fails - the machine can either land within the takeoff distance or continue (safely) to a suitable landing area, depending on when the failure occurs (that is, before or after CDP - see below). Group A helicopters must (with one engine out) clear all obstacles vertically by 35 feet, and climb (after CDP) at 100 fpm to 500 feet, then continue at 50 fpm (1.5%) between 500-1000. They must be able to maintain MOCA in the cruise.
However, there is an exposure time concept, measured in seconds, during which there is no guarantee of a flyaway or safe forced landing. The maximum permitted exposure time is a statistically derived figure, during which the probability of an engine failure can be discounted. The idea is to allow older helicopters to operate while new stuff comes in, and is due to expire (in JAA-land) in 2010.
JAR Class 2 machines, or Group A (Restricted), are slightly more flexible and can operate to a slightly less demanding regime, so you have a wider choice of landing sites. They have a limited exposure (although occupants and third parties must remain uninjured) - and can normally continue safely, except when the failure occurs early in the takeoff or late in the landing, so a forced landing may be required, under conditions that allow it, in terms of weather, light and terrain - those done from elevated pads in non-hostile conditions must be done by day only, otherwise you must abide by Class 1. Otherwise, cloud and visibility must be above 500 feet AGL and 800 m. In other words, up to 500 feet above the site level, you have to be able to see and avoid obstacles. After that, when you are presumed to be IMC, you must meet Class 1 requirements up to 1000 feet above the site, so watch your takeoff weight (the rate of climb should be 50 ft/min net).
JAR Class 3 multi-engined types (that is, Group B, for multis below 2730 kg) may have to make a forced landing, while single-engined types will (some multis share facilities and are not classed as real twins). Public Transport operations must be done in sight of the surface, by day, with at least a 600' ceiling. Minimum visibility is 800m. Class 3 is not allowed in IMC or at night. An engine failure below 100 feet should ensure a safe engine-off landing, so no manoeuvring should be done.
The JAR screen height is 35 feet, for takeoff and landing. There are no distance requirements.
I'm sure if I've got anything wrong someone will tell me!
Phil
Helicopters are certified in one of several groups. For example, JAR classifications are 1, 2 and 3, which are broadly equivalent to the UK Groups A, A(Restricted) and B (see the table below).
These are different from Airworthiness Groups, which dictate how well the airframe stands up to a forced landing. In other words, the terms Category A and Category B (as opposed to Group A or B, or Class 1 or 2) are for certification purposes:
Passengers JAR Class UK AN(G)R
Over 19 1 A
9-19 2 A (Restricted)*
Less than 9 3 B**
Category A means multi-engined helicopters with engine and system isolation as per JAR-27/29, and Flight Manual performance based on a critical engine failure concept providing adequate surface area and performance capability for continued safe flight if an engine fails. In other words, in addition to making sure you have power available (by restricting MAUW) it provides space for rejected takeoffs and landings, and obstacle clearance.
Category B means single- or multi-engined helicopters not fully meeting Category A. They are not guaranteed to stay airborne if an engine fails and an unscheduled landing is assumed, possibly with some damage.
Category A helicopters may operate in Performance Class 1, 2 or 3, but Category B machines may only be operated under Class 3.
JAR Class 1 (Group A) helicopters offer the highest protection for passengers and require no forced landing provisions if the critical power unit fails - the machine can either land within the takeoff distance or continue (safely) to a suitable landing area, depending on when the failure occurs (that is, before or after CDP - see below). Group A helicopters must (with one engine out) clear all obstacles vertically by 35 feet, and climb (after CDP) at 100 fpm to 500 feet, then continue at 50 fpm (1.5%) between 500-1000. They must be able to maintain MOCA in the cruise.
However, there is an exposure time concept, measured in seconds, during which there is no guarantee of a flyaway or safe forced landing. The maximum permitted exposure time is a statistically derived figure, during which the probability of an engine failure can be discounted. The idea is to allow older helicopters to operate while new stuff comes in, and is due to expire (in JAA-land) in 2010.
JAR Class 2 machines, or Group A (Restricted), are slightly more flexible and can operate to a slightly less demanding regime, so you have a wider choice of landing sites. They have a limited exposure (although occupants and third parties must remain uninjured) - and can normally continue safely, except when the failure occurs early in the takeoff or late in the landing, so a forced landing may be required, under conditions that allow it, in terms of weather, light and terrain - those done from elevated pads in non-hostile conditions must be done by day only, otherwise you must abide by Class 1. Otherwise, cloud and visibility must be above 500 feet AGL and 800 m. In other words, up to 500 feet above the site level, you have to be able to see and avoid obstacles. After that, when you are presumed to be IMC, you must meet Class 1 requirements up to 1000 feet above the site, so watch your takeoff weight (the rate of climb should be 50 ft/min net).
JAR Class 3 multi-engined types (that is, Group B, for multis below 2730 kg) may have to make a forced landing, while single-engined types will (some multis share facilities and are not classed as real twins). Public Transport operations must be done in sight of the surface, by day, with at least a 600' ceiling. Minimum visibility is 800m. Class 3 is not allowed in IMC or at night. An engine failure below 100 feet should ensure a safe engine-off landing, so no manoeuvring should be done.
The JAR screen height is 35 feet, for takeoff and landing. There are no distance requirements.
I'm sure if I've got anything wrong someone will tell me!
Phil
paco,
There are a number of points in your post which need clarification - you offered them up for comment and I will take up the challenge. Leaving aside UK BCARs (Group A and Group A Restricted) and concentrating on FAR/JAR 29, ICAO and JAR-OPS (which seeks to implement the Standards of ICAO), I offer the following:
Paco, this contention is not correct (and if nothing else is taken from this post perhaps this will stick) helicopter are certificated in Category A or Category B; they are operated in Performance Classes 1, 2 or 3.
Category A is a certification standard which provides assurance of continued flight in the event of a failure (using redundancy) or design assessment to reduce the probability of failure. Engine isolation ensures that one engine failure is unlikely to lead to a second, and fire in an engine compartment can be detected, contained and/or extinguished. Also required, for helicopter certificated under FAR/JAR 29, are more comprehensive flight and navigation instruments. Most of these requirements are also specified when smaller helicopters are certificated for Category A under Appendix C of FAR/JAR 27.
Category A also requires the provision of performance data so that One Engine Inoperative (OEI) obstacle clearance from take-off, through climb, cruise and landing can be calculated; this data includes: mass related take-off and landing procedures; heliport/helideck size limitations; distances and climb gradients (or rates of climb); and one-engine inoperative climb performance graphs. From these procedures and graphs an operator/pilot can establish a complete OEI flight trajectory.
The provisions of Category A give a level of confidence that the helicopter can be operated for continuous periods over a hostile environment without undue risk - the operational regulations (not the certification code) will specify whether operations can be conducted in PC1 or PC2 (which affects only the take-off and landing phases).
Category A helicopters may be operated in Performance Class 1, 2 or 3, but Category B machines may only be operated in Performance Class 3. It should be noted that it is Performance Class that specifies OEI obstacle clearance not the Category A procedure (this is always 35ft and not the (minimum of) 15ft that is permitted during the continued take-off of a Category A procedure).
Before moving on to procedures I would like to correct some more points; (1) the break between FAR/JAR 27/29 is 3175kg (and not the 2730kg implied by paco); and (2) there is no screen height used in JAR-OPS 3 although the end of the Take Off Distance Required (TODRH) can not be less than 35ft and the Landing Distance Required (LDRH) is taken from a point 50ft above the landing surface.
Group A and Performance Class 1 should not be contained in a single paragraph as they are two different ways of achieving engine failure accountability. To avoid further confusion only the FAR/JAR performance requirements will be quoted; they are:
There are basically three types of Category A procedure (different names may be used in Flight Manuals): the clear area; the restricted area; and the helipad (ground level and elevated).
The clear area procedure is basically a runway procedure and is always provided as it fulfils the minimum requirement for Category A data specified in FAR/JAR 27/29 (this data is used in PC1 and PC2) - once this is provided a manufacturer has a Category A helicopter. All distances will be provided with this procedure and will consist of: the Rejected Take-off Distance (RTOD); the Take-off Distance Required (TODRH); the Landing Distance Required (LDRH); the first and second segment climb performance data; and the distance to Vy at 200ft (the start of the second segment). This procedure normally uses a fixed Take-Off Decision Point (TDP) after which the helicopter becomes ‘go oriented’ (and before which an engine failure will result in a rejected take-off).
The restricted area (confined space) procedure can provided in a number of ways; an oblique steep climb procedure or a vertical climb procedure with an oblique rejected take-off are two. All distances will be provided as with the clear area. Features of this procedure are: access to variable Vtoss which can reduce the distances against a reduction in take-off mass; and/or a variable TDP which, as it is raised, will permit higher-obstacle clearance relative to the lowest point in the drop-down/min-dip (the min-dip must be shown to be 35ft above the highest obstacle in the continued take-off). The main restriction in this procedure is the amount of rejected take-off distance available as the oblique reject will eat more space as the height of the TDP increases.
The helipad procedures have a single common feature which is that the rejected take-off is restricted to the helipad itself. This procedure can be at ground level or elevated; these procedures feature a vertical or rearward climb which must allow sufficient visibility to provide a return to the take-off surface should an engine fails before TDP. The vertical climb element can be tailored to the application or for obstacle clearance: for offshore take-off where there are usually obstacles behind the helicopter, the vertical section is short and the TDP is not usually more than 30ft; for ground level or elevated heliports - where there are no obstacles behind the aircraft - the vertical section is in a rearward climb and the TDP can be set to any height which provides clearance over obstacles at min-dip. Obviously, drop down beyond the helipad following an engine failure after TDP can be used to gain speed - where obstacles permit.
As procedures become more sophisticated (configurable), they will provide a toolbox of profiles and graphs that can be tailored to any location - that point is being reached at the moment with the AB139 and the latest marks of the small twins (EC135, A109, B429 and MD902).
The definition of Performance Class 1 does not restrict the operator to applying a Category A procedure and obstacle clearance can be shown with alternative procedures. Provision of OEI HOGE performance will obviously divorce the procedure from a rejected take-off (and therefore any restriction on the size of the helipad (FATO)) but obstacle clearance in the continued take-off will have to be shown. The distances from the scheduled data of any Category A procedure can be used and is likely to be conservative.
I have not included any discussion on PC1 v PC2 as that was done to death on a previous thread.
Jim
There are a number of points in your post which need clarification - you offered them up for comment and I will take up the challenge. Leaving aside UK BCARs (Group A and Group A Restricted) and concentrating on FAR/JAR 29, ICAO and JAR-OPS (which seeks to implement the Standards of ICAO), I offer the following:
Helicopters are certified in one of several groups. For example, JAR classifications are 1, 2 and 3, which are broadly equivalent to the UK Groups A, A(Restricted) and B (see the table below).
Category A is a certification standard which provides assurance of continued flight in the event of a failure (using redundancy) or design assessment to reduce the probability of failure. Engine isolation ensures that one engine failure is unlikely to lead to a second, and fire in an engine compartment can be detected, contained and/or extinguished. Also required, for helicopter certificated under FAR/JAR 29, are more comprehensive flight and navigation instruments. Most of these requirements are also specified when smaller helicopters are certificated for Category A under Appendix C of FAR/JAR 27.
Category A also requires the provision of performance data so that One Engine Inoperative (OEI) obstacle clearance from take-off, through climb, cruise and landing can be calculated; this data includes: mass related take-off and landing procedures; heliport/helideck size limitations; distances and climb gradients (or rates of climb); and one-engine inoperative climb performance graphs. From these procedures and graphs an operator/pilot can establish a complete OEI flight trajectory.
The provisions of Category A give a level of confidence that the helicopter can be operated for continuous periods over a hostile environment without undue risk - the operational regulations (not the certification code) will specify whether operations can be conducted in PC1 or PC2 (which affects only the take-off and landing phases).
Category A helicopters may be operated in Performance Class 1, 2 or 3, but Category B machines may only be operated in Performance Class 3. It should be noted that it is Performance Class that specifies OEI obstacle clearance not the Category A procedure (this is always 35ft and not the (minimum of) 15ft that is permitted during the continued take-off of a Category A procedure).
Before moving on to procedures I would like to correct some more points; (1) the break between FAR/JAR 27/29 is 3175kg (and not the 2730kg implied by paco); and (2) there is no screen height used in JAR-OPS 3 although the end of the Take Off Distance Required (TODRH) can not be less than 35ft and the Landing Distance Required (LDRH) is taken from a point 50ft above the landing surface.
Group A and Performance Class 1 should not be contained in a single paragraph as they are two different ways of achieving engine failure accountability. To avoid further confusion only the FAR/JAR performance requirements will be quoted; they are:
There are basically three types of Category A procedure (different names may be used in Flight Manuals): the clear area; the restricted area; and the helipad (ground level and elevated).
The clear area procedure is basically a runway procedure and is always provided as it fulfils the minimum requirement for Category A data specified in FAR/JAR 27/29 (this data is used in PC1 and PC2) - once this is provided a manufacturer has a Category A helicopter. All distances will be provided with this procedure and will consist of: the Rejected Take-off Distance (RTOD); the Take-off Distance Required (TODRH); the Landing Distance Required (LDRH); the first and second segment climb performance data; and the distance to Vy at 200ft (the start of the second segment). This procedure normally uses a fixed Take-Off Decision Point (TDP) after which the helicopter becomes ‘go oriented’ (and before which an engine failure will result in a rejected take-off).
The restricted area (confined space) procedure can provided in a number of ways; an oblique steep climb procedure or a vertical climb procedure with an oblique rejected take-off are two. All distances will be provided as with the clear area. Features of this procedure are: access to variable Vtoss which can reduce the distances against a reduction in take-off mass; and/or a variable TDP which, as it is raised, will permit higher-obstacle clearance relative to the lowest point in the drop-down/min-dip (the min-dip must be shown to be 35ft above the highest obstacle in the continued take-off). The main restriction in this procedure is the amount of rejected take-off distance available as the oblique reject will eat more space as the height of the TDP increases.
The helipad procedures have a single common feature which is that the rejected take-off is restricted to the helipad itself. This procedure can be at ground level or elevated; these procedures feature a vertical or rearward climb which must allow sufficient visibility to provide a return to the take-off surface should an engine fails before TDP. The vertical climb element can be tailored to the application or for obstacle clearance: for offshore take-off where there are usually obstacles behind the helicopter, the vertical section is short and the TDP is not usually more than 30ft; for ground level or elevated heliports - where there are no obstacles behind the aircraft - the vertical section is in a rearward climb and the TDP can be set to any height which provides clearance over obstacles at min-dip. Obviously, drop down beyond the helipad following an engine failure after TDP can be used to gain speed - where obstacles permit.
As procedures become more sophisticated (configurable), they will provide a toolbox of profiles and graphs that can be tailored to any location - that point is being reached at the moment with the AB139 and the latest marks of the small twins (EC135, A109, B429 and MD902).
The definition of Performance Class 1 does not restrict the operator to applying a Category A procedure and obstacle clearance can be shown with alternative procedures. Provision of OEI HOGE performance will obviously divorce the procedure from a rejected take-off (and therefore any restriction on the size of the helipad (FATO)) but obstacle clearance in the continued take-off will have to be shown. The distances from the scheduled data of any Category A procedure can be used and is likely to be conservative.
I have not included any discussion on PC1 v PC2 as that was done to death on a previous thread.
Jim
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Jim
Thanks for the detailed explanation here. Two points.
Firstly, when requesting a strictly Helipad Procedure departure profile from ATC, what is the correct request to ATC; I assume simply for a "helipad departure", rather than Cat A /Group A/Class 1 departure?
Secondly, to achieve Category A certification, with reference to rejects before TDP following a helipad procedure, what criteria for subsequent life/durability to engines and transmissions are specified/involved? Of course the acft must be operated within all the transient OEI limits in the FM, but when a manufacturer specifies a say 15 second power limit OEI, which is likely to be the limiting factor on a reject, what reduction if any to the TBO of engine/transmissions follow full use of that transient limit?
On the face of it, this is a manufacturer question, but presumably the regulating authorities have specifications that prevent a manufacturer simply taking the view that the transient OEI limit is one that has a say 90% chance of the engine/transmission not failing in such use, though must inevitably then be immediately deemed unservicable and over-hauled?
Thanks for the detailed explanation here. Two points.
Firstly, when requesting a strictly Helipad Procedure departure profile from ATC, what is the correct request to ATC; I assume simply for a "helipad departure", rather than Cat A /Group A/Class 1 departure?
Secondly, to achieve Category A certification, with reference to rejects before TDP following a helipad procedure, what criteria for subsequent life/durability to engines and transmissions are specified/involved? Of course the acft must be operated within all the transient OEI limits in the FM, but when a manufacturer specifies a say 15 second power limit OEI, which is likely to be the limiting factor on a reject, what reduction if any to the TBO of engine/transmissions follow full use of that transient limit?
On the face of it, this is a manufacturer question, but presumably the regulating authorities have specifications that prevent a manufacturer simply taking the view that the transient OEI limit is one that has a say 90% chance of the engine/transmission not failing in such use, though must inevitably then be immediately deemed unservicable and over-hauled?
Last edited by rotorspeed; 9th Apr 2005 at 19:06.
rotorspeed,
Provided ATC know what to expect - the call is immaterial.
The Flight Manual always contains the conditions under which engine limits may be used. The only short term OEI limits that I am aware of are the 30 second plus the 2 minute limit - or for those which do not have a 30 second limit, the 2.5 minute limit (note that the AB139 does not use a 30 second limit - presumably because it is not required).
A rejected take-off is unlikely to come anywhere near that time - unlike the continued take-off where the limits have to be observed and not exceeded. One of the problems seen in the recent past is the reluctance to pull up to limits by drooping the rotors on a reject - with the consequence of an increasing rate of descent and a hard landing. Fortunately most of the occurrences were in training and not during operations.
Depending on the engine, the use of the 30 second limit might result in maintenance procedures (I think that 212man has had something to say about that in the past with the EC155) but is unlikely to have a severe affect on the gearbox.
Whatever the consequence it will have been pre-considered by the State of Design and the Type Certificate Holder and have been part of the certification process - and addressed in the Flight Manual or the Maintenance Procedures.
Most of the profiles/procedures that I described in my last post and PC2e (offshore zero exposure departures), benefit from the use of FADEC (which protects the remaining engine and the transmission) and the stored energy provided by the additional NR.
There have been discussions on FADEC limit override but I am not aware that this has led to changes to FADEC algorithms - that and blow-away power are really tools of last resort.
Jim
Provided ATC know what to expect - the call is immaterial.
The Flight Manual always contains the conditions under which engine limits may be used. The only short term OEI limits that I am aware of are the 30 second plus the 2 minute limit - or for those which do not have a 30 second limit, the 2.5 minute limit (note that the AB139 does not use a 30 second limit - presumably because it is not required).
A rejected take-off is unlikely to come anywhere near that time - unlike the continued take-off where the limits have to be observed and not exceeded. One of the problems seen in the recent past is the reluctance to pull up to limits by drooping the rotors on a reject - with the consequence of an increasing rate of descent and a hard landing. Fortunately most of the occurrences were in training and not during operations.
Depending on the engine, the use of the 30 second limit might result in maintenance procedures (I think that 212man has had something to say about that in the past with the EC155) but is unlikely to have a severe affect on the gearbox.
Whatever the consequence it will have been pre-considered by the State of Design and the Type Certificate Holder and have been part of the certification process - and addressed in the Flight Manual or the Maintenance Procedures.
Most of the profiles/procedures that I described in my last post and PC2e (offshore zero exposure departures), benefit from the use of FADEC (which protects the remaining engine and the transmission) and the stored energy provided by the additional NR.
There have been discussions on FADEC limit override but I am not aware that this has led to changes to FADEC algorithms - that and blow-away power are really tools of last resort.
Jim
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Jim
Thanks. The AS355N actually has a 15 second limit of 140% Tq OEI, (131% 2m 30 sec), so on a reject I assumed this would be the factor that determined max weight for Cat A ops. It would be useful to know how much of a bill might be incurred pulling that, so I'll check with maintenance! Somehow doubt the FADEC on this acft protects from exceeding the engine limits, resulting in Nr droop.
Are you saying that in some acft the FADEC will prevent exceedances in OEI conditions, even though the absence of that might protect the airframe and occupants, even if it trashes an engine? Assuming extreme circumstances, of course.
Thanks. The AS355N actually has a 15 second limit of 140% Tq OEI, (131% 2m 30 sec), so on a reject I assumed this would be the factor that determined max weight for Cat A ops. It would be useful to know how much of a bill might be incurred pulling that, so I'll check with maintenance! Somehow doubt the FADEC on this acft protects from exceeding the engine limits, resulting in Nr droop.
Are you saying that in some acft the FADEC will prevent exceedances in OEI conditions, even though the absence of that might protect the airframe and occupants, even if it trashes an engine? Assuming extreme circumstances, of course.
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thanks jiml - that made a couple of points clearer, though there has always been some confusion in the use of the words group and category interchangeably for certification and performance purposes
"Paco, this contention is not correct (and if nothing else is taken from this post perhaps this will stick) helicopter are certificated in Category A or Category B; they are operated in Performance Classes 1, 2 or 3."
That's exactly what I said!
"In other words, the terms Category A and Category B (as opposed to Group A or B, or Class 1 or 2) are for certification purposes"
So what do people mean when they say Cat A performance?
phil
"Paco, this contention is not correct (and if nothing else is taken from this post perhaps this will stick) helicopter are certificated in Category A or Category B; they are operated in Performance Classes 1, 2 or 3."
That's exactly what I said!
"In other words, the terms Category A and Category B (as opposed to Group A or B, or Class 1 or 2) are for certification purposes"
So what do people mean when they say Cat A performance?
phil
Last edited by paco; 9th Apr 2005 at 19:16.
A couple of points about the engine ratings etc.
Jim, I may be wrong but I would guess the reason the AB-139 does not have a 30 second rating is because it uses the PT-6. Generally the engines with 30 second ratings have new technology materials (such as single crystal blades etc) and I doubt that even the -67 version would have this.
The point made about FADEC controlled engines limiting power at the expense of the airframe is a bit misleading I feel. For the type I am familiar with (EC-155 which has dual channel FADEC and no cockpit engine control other than a switch) when operting in twin engine operations (AEO) the FADECs will normally control the engines such that they remain within the normal AEO limits. However, that is not to say that they will respect the transmission limits and so it is still possible to 'overtorque' the MGB to prevent mishaps. If this proves to still be not enough power to prevent the problem, and continued application of collective results in the Nr drooping, the FADECs will abandon the AEO limits and apply the OEI 2 minute limits.
If this still proves insufficient then tough!
The point I feel is misleading, though, is that this latter case is no different to a conventionally governed engine where if you pull in a big handful of collective, both engines will provide power up to the maximum contingency rating (2.5 minute) but no more. It's the same situation. The difference is that one limit is applied through the computer whereas the other is the topping setting set mechanically within the governing unit (AFCU).
Now, if you really want to see a system with an odd priority, look at the B-212 where the AFCU is designed to save the gearbox at the expense of the airframe. If you apply collective above 104.3% TQ the AFCU will prevent the engines producing more power. In fact it's worse than that; because the AFCU is respecting a torque limitation, if you droop the Nr (which you probably will do to prevent a heavy landing) the N2 will drop and so for a given torque value the actual SHP will be less. So the situation will escalate.
Jim, I may be wrong but I would guess the reason the AB-139 does not have a 30 second rating is because it uses the PT-6. Generally the engines with 30 second ratings have new technology materials (such as single crystal blades etc) and I doubt that even the -67 version would have this.
The point made about FADEC controlled engines limiting power at the expense of the airframe is a bit misleading I feel. For the type I am familiar with (EC-155 which has dual channel FADEC and no cockpit engine control other than a switch) when operting in twin engine operations (AEO) the FADECs will normally control the engines such that they remain within the normal AEO limits. However, that is not to say that they will respect the transmission limits and so it is still possible to 'overtorque' the MGB to prevent mishaps. If this proves to still be not enough power to prevent the problem, and continued application of collective results in the Nr drooping, the FADECs will abandon the AEO limits and apply the OEI 2 minute limits.
If this still proves insufficient then tough!
The point I feel is misleading, though, is that this latter case is no different to a conventionally governed engine where if you pull in a big handful of collective, both engines will provide power up to the maximum contingency rating (2.5 minute) but no more. It's the same situation. The difference is that one limit is applied through the computer whereas the other is the topping setting set mechanically within the governing unit (AFCU).
Now, if you really want to see a system with an odd priority, look at the B-212 where the AFCU is designed to save the gearbox at the expense of the airframe. If you apply collective above 104.3% TQ the AFCU will prevent the engines producing more power. In fact it's worse than that; because the AFCU is respecting a torque limitation, if you droop the Nr (which you probably will do to prevent a heavy landing) the N2 will drop and so for a given torque value the actual SHP will be less. So the situation will escalate.
paco,
I think that I have already covered your question in my first post:
and is the provision of procedures, masses and data in compliance with the respective rules of FAR/JAR 29.45 - 29.67 to the satisfaction of the Certificating Authority. This set of rules specify (along with the guidance in AC 29-2C): no descent below 15ft (when the TDP is above 15ft) in the take-off path; require a level surface over which the take-off is being conducted; no obstacles in the 'Takeoff path'; the provision of the minimum climb performance - i.e. 100ft/min up to 200ft at Vtoss and 150ft/min at 1000ft at Vy; and the provision of the respective distances. None of that is in question, the point that was being made was more fundamental - when, what and how?
When is the operator required to apply the performance data, what obstacle clearance has to be shown and where is that specified? Clearly there is a difference of opinion as the highlighted section in the definition of Category A between the FAA and the JAA/ICAO indicates:
The JAA clearly believes that the provision of performance data must be supplemented by the appropriate operating rules in the JARs. The FAA does not as there are no helicopter performance rules in FAR 91 or 135 (unlike Appendix A to FAR 135 for 10 or more passenger airplanes).
It is the operational regulation which must indicate how an operation can be conducted; certainly JAR-OPS contains not only the indication when to operate within a certain Performance Class but also provides the requirements, compliance with which will give appropriate obstacle clearance in PC1 (and PC2 - outside of the take-off and landing phases).
In the absence of performance rules in the operational FARs, the FAA have to rely upon an interpretation of FAR 29.1 and in particular FAR 29.1(c):
All who followed the debate on the earlier thread will understand the implication of that. This is not a problem with JAR-OPS as operations in Performance Class 2 can be conducted when the number of passenger seats is 19 or below. For operations under FARs this has also been set aside for the time being with the issue of OpSpec H100 - which in other terms, specifies PC2 for offshore operations.
212man,
Yes on re-reading my earlier post I gave the wrong impression - it is only the engines that are controlled.
Jim
PS Edited on 18th April for clarity.
I think that I have already covered your question in my first post:
Category A also requires the provision of performance data so that One Engine Inoperative (OEI) obstacle clearance from take-off, through climb, cruise and landing can be calculated; this data includes: mass related take-off and landing procedures; heliport/helideck size limitations; distances and climb gradients (or rates of climb); and one-engine inoperative climb performance graphs. From these procedures and graphs an operator/pilot can establish a complete OEI flight trajectory.
When is the operator required to apply the performance data, what obstacle clearance has to be shown and where is that specified? Clearly there is a difference of opinion as the highlighted section in the definition of Category A between the FAA and the JAA/ICAO indicates:
(JAA) Category A, with respect to rotorcraft, means a multi-engined rotorcraft designed with engine and system isolation features specified in JAR–27 / JAR–29 and capable of operations using take-off and landing data scheduled under a critical engine failure concept which assures adequate designated surface area and adequate performance capability for continued safe flight or safe rejected take-off in the event of engine failure.
(FAA) Category A, with respect to transport category rotorcraft, means multiengine rotorcraft designed with engine and system isolation features specified in Part 29 and utilizing scheduled takeoff and landing operations under a critical engine failure concept which assures adequate designated surface area and adequate performance capability for continued safe flight in the event of engine failure.
(FAA) Category A, with respect to transport category rotorcraft, means multiengine rotorcraft designed with engine and system isolation features specified in Part 29 and utilizing scheduled takeoff and landing operations under a critical engine failure concept which assures adequate designated surface area and adequate performance capability for continued safe flight in the event of engine failure.
It is the operational regulation which must indicate how an operation can be conducted; certainly JAR-OPS contains not only the indication when to operate within a certain Performance Class but also provides the requirements, compliance with which will give appropriate obstacle clearance in PC1 (and PC2 - outside of the take-off and landing phases).
In the absence of performance rules in the operational FARs, the FAA have to rely upon an interpretation of FAR 29.1 and in particular FAR 29.1(c):
All who followed the debate on the earlier thread will understand the implication of that. This is not a problem with JAR-OPS as operations in Performance Class 2 can be conducted when the number of passenger seats is 19 or below. For operations under FARs this has also been set aside for the time being with the issue of OpSpec H100 - which in other terms, specifies PC2 for offshore operations.
212man,
Yes on re-reading my earlier post I gave the wrong impression - it is only the engines that are controlled.
Jim
PS Edited on 18th April for clarity.
Last edited by JimL; 18th Apr 2005 at 08:26.
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One of the reasons why a manufacturer may choose not to use the 30 second ratings is that the transients allowed for this rating may not be as large as those allowed if you use the 2.5 minute ratings. (Go figure...)
For certification purposes, transients are not allowed to be used to demonstrate performance, and even for category A machines, you cannot use the 30 second rating for the takeoff engine failure portion (strange as this may seem - read the Part 29 sections if you don't believe me).
While this is a strange way to do things, it means that in a real engine failure you will have better performance than in the flight manual, which is a comforting thought.
For certification purposes, transients are not allowed to be used to demonstrate performance, and even for category A machines, you cannot use the 30 second rating for the takeoff engine failure portion (strange as this may seem - read the Part 29 sections if you don't believe me).
While this is a strange way to do things, it means that in a real engine failure you will have better performance than in the flight manual, which is a comforting thought.
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Cat A vs Perf Class 1 and OEI Hover
Thanks for all the input - in essence it appears there is a lot of debate surrounding why Cat A and Perf Class 1 and what term is used when.
Am I correct in saying:
Cat A is a set of certification criteria
Perf Class 1 implies you will have a successful departure/landing in the event of a critical power unit failure and indeed be able to stay aloft en route at the time of flight, BUT -
It still appears that Cat A is often referred to as the profile and as such can be either a towering one (with reversal) for say rigs/helidecks or an acceleration to Vtoss for a departure from a field - which allows for a safe reject.
SO in a nutshell - your aircraft is Cat A cetified but to be Perf Class 1 compliant you need to follow a particular profile on take-off or landing, which may require a reversal and then you need to ensure that you can stay aloft en-route.
THe other great Q that was posed is that of Cat A implying OEI hover capability - Me thinks not??????
Now for the interesting part - how is the A109 Power/K2 a Category A "equivalent" aircraft. Is this purely because the Part 29 def of Cat A is for large transport helicopters??
Am I correct in saying:
Cat A is a set of certification criteria
Perf Class 1 implies you will have a successful departure/landing in the event of a critical power unit failure and indeed be able to stay aloft en route at the time of flight, BUT -
It still appears that Cat A is often referred to as the profile and as such can be either a towering one (with reversal) for say rigs/helidecks or an acceleration to Vtoss for a departure from a field - which allows for a safe reject.
SO in a nutshell - your aircraft is Cat A cetified but to be Perf Class 1 compliant you need to follow a particular profile on take-off or landing, which may require a reversal and then you need to ensure that you can stay aloft en-route.
THe other great Q that was posed is that of Cat A implying OEI hover capability - Me thinks not??????
Now for the interesting part - how is the A109 Power/K2 a Category A "equivalent" aircraft. Is this purely because the Part 29 def of Cat A is for large transport helicopters??
canthover,
Yes, Category A is a set of certificating criteria.
Yes, PC1 provides engine failure accountability in all phases of flight - however a little more can be said:
The proposed revised definition of PC1 in ICAO:
Helideck/rig procedures can never use back-up as it is too dangerous (vertical sections greater than 20ft cause problems as the pilot has a tendency to move back to keep the deck in sight).
Don’t dismiss OEI HOGE as the small twins are beginning to have this capability; Category A procedures come with a minimum helipad size; the ability to hover on one engine removes this limitation whilst still permitting PC1 (there are many (small) elevated heliports in Europe which can benefit from such a capability).
To my knowledge the A109 Power and K2 have full Category A certification in compliance with Appendix C of FAR/JAR 27 (which calls up a number of rules from FAR/JAR 29). Aircraft which were certificated before Appendix C of FAR 27 (or in compliance with the FAA AC) do not meet the airworthiness requirements. These aircraft include early marks of the AS355, the A109 and the Bo105 - some of which like the Bo105 have an STC which, when applied, can provide an equivalence that is accepted in JAR-OPS 3.
Even after the advent of Appendix C to FAR/JAR 27, some manufacturers did not apply for certification under Appendix C - the B427 comes into that category as does the MD900 - hence the B429 and the MD902. To operate in PC1 or PC2 in Europe, a helicopter has to be certificated in Category A.
Yes, Category A is a set of certificating criteria.
Yes, PC1 provides engine failure accountability in all phases of flight - however a little more can be said:
The proposed revised definition of PC1 in ICAO:
Helideck/rig procedures can never use back-up as it is too dangerous (vertical sections greater than 20ft cause problems as the pilot has a tendency to move back to keep the deck in sight).
Don’t dismiss OEI HOGE as the small twins are beginning to have this capability; Category A procedures come with a minimum helipad size; the ability to hover on one engine removes this limitation whilst still permitting PC1 (there are many (small) elevated heliports in Europe which can benefit from such a capability).
To my knowledge the A109 Power and K2 have full Category A certification in compliance with Appendix C of FAR/JAR 27 (which calls up a number of rules from FAR/JAR 29). Aircraft which were certificated before Appendix C of FAR 27 (or in compliance with the FAA AC) do not meet the airworthiness requirements. These aircraft include early marks of the AS355, the A109 and the Bo105 - some of which like the Bo105 have an STC which, when applied, can provide an equivalence that is accepted in JAR-OPS 3.
Even after the advent of Appendix C to FAR/JAR 27, some manufacturers did not apply for certification under Appendix C - the B427 comes into that category as does the MD900 - hence the B429 and the MD902. To operate in PC1 or PC2 in Europe, a helicopter has to be certificated in Category A.
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All very confusing
Thanks for the info - all makes sense BUT - maybe I am being thick here:
I had a look at the A109K2 RCFM (page 7 of App 25) says it is not certified to JAR 27 CAT A, but shows a whole whack of profiles for take-offs less than and greater than 2720 kilograms - so CAT A can be done as a back up or from a clear area with gauranteed safe reject.
A quick peek at the CAT A back up (30 m recommended) appears to be for elevated helipads (helidecks). I presume then that there is no vertical climb profile that exists for the aircraft which is typical of the rig departure profile.
I had a look at the A109K2 RCFM (page 7 of App 25) says it is not certified to JAR 27 CAT A, but shows a whole whack of profiles for take-offs less than and greater than 2720 kilograms - so CAT A can be done as a back up or from a clear area with gauranteed safe reject.
A quick peek at the CAT A back up (30 m recommended) appears to be for elevated helipads (helidecks). I presume then that there is no vertical climb profile that exists for the aircraft which is typical of the rig departure profile.