Category A PC1 or PC2
Join Date: Nov 2000
Location: White Waltham, Prestwick & Calgary
Age: 72
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Alexandre - thank you for your question, but I also agree with this paying too much lip service to engine failure, when you would be in the wrong position for other failures which have a higher category of risk, and a machine that's not as crashworthy as another - and as usual, SASLess makes a very good point. I have always regarded a twin as only being safer when one engine fails - it's not safer just because it's got two engines, which is a problem when it comes to legal liability and the choice between using a 206 or a 355, for example. However much the rules might have been valid way back when, things change and the Authorities don't catch up, largely because the people in charge often don't understand the basics anyway and are afraid to change things (the red flag here is that you say they want you to operate in Cat A - my understanding is that is a certification standard that concerns itself with how the helicopter is built, and PC1/PC2 is built on it).
I have never been a big fan of backwards takeoffs - it's hard on the engines, and I don't feel comfortable going backwards downwind in an avoid curve (yeah, I know everyone pretends if you do it dynamically you are not in it but if you lose an engine, you are. It's difficult because you have to keep inside a profile but outside the H/V curve
). I understand they allow you to use the only good landing site for miles around, but I wouldn't want to go backwards without a crewman in those situations anyway.
I have never been a big fan of backwards takeoffs - it's hard on the engines, and I don't feel comfortable going backwards downwind in an avoid curve (yeah, I know everyone pretends if you do it dynamically you are not in it but if you lose an engine, you are. It's difficult because you have to keep inside a profile but outside the H/V curve
). I understand they allow you to use the only good landing site for miles around, but I wouldn't want to go backwards without a crewman in those situations anyway.
Last edited by paco; 30th May 2023 at 07:46.
Thread Starter
If anyone is interested in learning more about our regulatory agency's view on performance, I'll leave a link to an article.
https://www.scielo.br/j/jatm/a/ZmPfC...at=pdf&lang=en
It would be great to know your views on the matter.
https://www.scielo.br/j/jatm/a/ZmPfC...at=pdf&lang=en
It would be great to know your views on the matter.
Thanks for the paper Vidual.
An interesting paper (because it contains a great deal of information - albeit with some small errors and notable omissions) but, in my view, one that reaches the wrong conclusion.
It is unlikely that a Category A procedure for offshore operations (enforced PC1) will ever be practical for a number of reasons - which include: the necessity keep the landing surface in sight during the initial climb manoeuvre (to retain the ability to rejected without damage) and the lack of space to do other than initially to climb vertically - until losing sight of the deck (shown in the 1990s to be about 20ft - which has been stretched by the OEMs to 30ft); the requirement to miss the deck edge by 15ft during the continued take-off; the ability to remain 35ft above the surface of the water in all conditions; the small size of the FATO/TLOF; the 'obstacle environment'/'wind direction' issue; and, finally, the unrealistic expectation that the installed power will ever allow OEI hover performance in zero wind (which is required if PC1 is ever to be enforced).
Jim
An interesting paper (because it contains a great deal of information - albeit with some small errors and notable omissions) but, in my view, one that reaches the wrong conclusion.
It is unlikely that a Category A procedure for offshore operations (enforced PC1) will ever be practical for a number of reasons - which include: the necessity keep the landing surface in sight during the initial climb manoeuvre (to retain the ability to rejected without damage) and the lack of space to do other than initially to climb vertically - until losing sight of the deck (shown in the 1990s to be about 20ft - which has been stretched by the OEMs to 30ft); the requirement to miss the deck edge by 15ft during the continued take-off; the ability to remain 35ft above the surface of the water in all conditions; the small size of the FATO/TLOF; the 'obstacle environment'/'wind direction' issue; and, finally, the unrealistic expectation that the installed power will ever allow OEI hover performance in zero wind (which is required if PC1 is ever to be enforced).
Jim
The Lightbulb illuminates....short simple explanation even this old Dinosaur can understand.
I was struggling trying to figure out what was being said in that Paper especially when it noted the author had differences with your views.
Is there anything to the apparent concern about the US FAA method of placing Performance Data in the "Limitations Section" of a RFM or did I misunderstand that part of the paper?
I was struggling trying to figure out what was being said in that Paper especially when it noted the author had differences with your views.
Is there anything to the apparent concern about the US FAA method of placing Performance Data in the "Limitations Section" of a RFM or did I misunderstand that part of the paper?
The answer is: Not always for the reasons previously explained in this thread. You noted that you can operate in PC1 at 26,500 lb, at sea level, 32C, using the maximum TDP/Vtoss, but that you have to reduce the gross weight if the temperature goes above 32C. The only way to make the first segment climb requirement not limiting at temperatures above 32C is to increase the TDP/Vtoss. To satisfy your curiosity you should be able to see how much TDP/Vtoss would have to be increased (theoretically) by graphically extrapolating the performance charts.
What I am reminded of, though, is an anomaly in the RFM performance graphs that I tried to correct some years ago. In fact, it was amended, but was subsequently restored in a later update, for some reason. Basically, the Cat A WAT graph states a maximum permitted Vtoss of 62/63 kts (can't recall exactly), with the associated maximum Vtdp which then, by definition, can be considered a limitation. However, the graphs used for calculating rejected and continued take off distances allow a Vtdp of 55 kts, with 70 kts Vtoss. Discussions at the time revealed that the maximum Vtoss stated was actually the speed above which no further increase in MTOM would be achieved, and so was the demarcation between 1st segment limiting and 2nd segment limiting performance. As I say, there was a period when this "maximum permitted" statement was removed, but it reappeared later. Regardless, when I set the criteria for our FATO upgrade, I stipulated a length of 810m as this was the nil wind rejected take off distance for a 55 kts TDP!
All States accept the placing of performance within the Limitations (or within section 1 of the manual). This is only an issue with regard to the limitation of the HV Diagram when the aircraft is operated outside of a Category A procedure.
The probability of having a Category A procedure for offshore operations is vanishingly small (for the reasons stated in my previous post). The very nature of helidecks therefore means that during take-off and landing there will be an incursion into the HV diagram (just think it through). The requirement to apply the limitations of the RFM is (almost always) placed in the basic regulations of the State. If the HV diagram is within the limitations section, the pilot will be in contravention of this limitation. This means that, for those States who understand and recognise the issues of offshore operations, an alleviation must be provided to avoid deliberate breaching of the regulations.
The FAA avoids this situation by alleviating from this limitation in FAR 91.9(d) - but only for operations over water. The JAA copied this alleviation into JAR-OPS; during the transposition of JARs to EASA OPS, this was removed - which left all offshore pilots in deliberate breach. After a convoluted discussion where unrealistic alternatives (amendment of Part 29) were proposed, EASA amended the basic regulation to contain an alleviation. similar to that previously written. The difference now is that the FAA only allow this over water but EASA allow it universally (in accordance with the Code of Performance). In addition, the FAA, recognising the difficulties of offshore offshore operations have OpsSpec H 100.
In the paper it is rightly stated that formerly, Category A helicopters were certificated with only the clear area procedure (runway-type). At the time that FAR 29 was written, it was thought that helicopter would only be operated from airfields (the same was true of ICAO Annexes 6, 8 and 14). That this was not true was accepted and FAR 29 was amended as part of NPA 80-25. Realistically, Part 29 has not changed in substance since then. The changes made to Part 29.1 presaged the introduction of the Performance Classes - as the paper stated, Category A, Category B and a hybrid (Performance Class 2).
Even though NPA 80-25 recognised that operations to other than runways would become the norm in the future, the nature of that change was not apparent. Chapter 2 provides a framework for Category A procedures that is completely objective and has no knowledge of the use to which it will be put. Procedures could be provided to suit any operational requirement; it provides a facility for provision of procedures not a compulsion - i.e. a capability. The manufacturer provides a suite of Category A procedures; if required by the Code of Performance, the operator uses one of these procedures and adapts it to the obstacle environment.
In fact, procedures are split into two types: the runway-type - the clear area procedure (very similar to fixed wing); or vertical procedures - where the profile requires a vertical component - i.e. the ascent to the TDP or the descent from the LDP. This vertical component allows the building of potential energy (the height of the TDP) that can be converted to kinetic energy (speed of the helicopter) whilst accelerating over obstacles to reach a speed that permits a safe climb. It is this unique capability of the helicopter (including eVTOL) that allows operations from small heliports (ground level or elevated) in virtually any obstacle environment.
To return to offshore operations: a Category A procedure meeting all of the clauses of Part 29, Chapter 2 and suiting the helideck environmental conditions set out previously would required the power of a Wessex (which could take-off, fly, and land on one engine). The helideck environment has neither the facilities of a runway nor the ability to apply vertical procedures that permit the helicopter to achieve engine failure accountability at reasonable operating masses. It is, and will remain, an outrider that has to be addressed with realistic solutions.
The probability of having a Category A procedure for offshore operations is vanishingly small (for the reasons stated in my previous post). The very nature of helidecks therefore means that during take-off and landing there will be an incursion into the HV diagram (just think it through). The requirement to apply the limitations of the RFM is (almost always) placed in the basic regulations of the State. If the HV diagram is within the limitations section, the pilot will be in contravention of this limitation. This means that, for those States who understand and recognise the issues of offshore operations, an alleviation must be provided to avoid deliberate breaching of the regulations.
The FAA avoids this situation by alleviating from this limitation in FAR 91.9(d) - but only for operations over water. The JAA copied this alleviation into JAR-OPS; during the transposition of JARs to EASA OPS, this was removed - which left all offshore pilots in deliberate breach. After a convoluted discussion where unrealistic alternatives (amendment of Part 29) were proposed, EASA amended the basic regulation to contain an alleviation. similar to that previously written. The difference now is that the FAA only allow this over water but EASA allow it universally (in accordance with the Code of Performance). In addition, the FAA, recognising the difficulties of offshore offshore operations have OpsSpec H 100.
In the paper it is rightly stated that formerly, Category A helicopters were certificated with only the clear area procedure (runway-type). At the time that FAR 29 was written, it was thought that helicopter would only be operated from airfields (the same was true of ICAO Annexes 6, 8 and 14). That this was not true was accepted and FAR 29 was amended as part of NPA 80-25. Realistically, Part 29 has not changed in substance since then. The changes made to Part 29.1 presaged the introduction of the Performance Classes - as the paper stated, Category A, Category B and a hybrid (Performance Class 2).
Even though NPA 80-25 recognised that operations to other than runways would become the norm in the future, the nature of that change was not apparent. Chapter 2 provides a framework for Category A procedures that is completely objective and has no knowledge of the use to which it will be put. Procedures could be provided to suit any operational requirement; it provides a facility for provision of procedures not a compulsion - i.e. a capability. The manufacturer provides a suite of Category A procedures; if required by the Code of Performance, the operator uses one of these procedures and adapts it to the obstacle environment.
In fact, procedures are split into two types: the runway-type - the clear area procedure (very similar to fixed wing); or vertical procedures - where the profile requires a vertical component - i.e. the ascent to the TDP or the descent from the LDP. This vertical component allows the building of potential energy (the height of the TDP) that can be converted to kinetic energy (speed of the helicopter) whilst accelerating over obstacles to reach a speed that permits a safe climb. It is this unique capability of the helicopter (including eVTOL) that allows operations from small heliports (ground level or elevated) in virtually any obstacle environment.
To return to offshore operations: a Category A procedure meeting all of the clauses of Part 29, Chapter 2 and suiting the helideck environmental conditions set out previously would required the power of a Wessex (which could take-off, fly, and land on one engine). The helideck environment has neither the facilities of a runway nor the ability to apply vertical procedures that permit the helicopter to achieve engine failure accountability at reasonable operating masses. It is, and will remain, an outrider that has to be addressed with realistic solutions.
Thread Starter
"The FAA avoids this situation by alleviating from this limitation in FAR 91.9(d) - but only for operations over water." - Same thing here in Brazil.
Jim,
I believe that something that can be added to the content is the Operations without an assured safe forced landing capability (OpsSpec H 305?). Could you write something about it?
I found this Advisory Circular from CASA:
https://www.google.com/url?sa=t&rct=...--F1nH32pflzgH
FAA has already authorized Bristow to operate in this manner. Can we consider a breakthrough? Should other countries follow?
https://www.google.com/url?sa=t&rct=...qioq8TNreJjOyc
212man,
"The Category Ahorizontal takeoff procedure shown diagrammatically in Figure 4-7 features variable Takeoff Decision Points (TDP) and Takeoff Safety Speeds (Vtoss). The TDP, expressed only in terms of airspeed, is selectable in 1 knot increments between 30 and 48 knots. Vtoss is TDP + 15 knots. This permits payload to be traded off against available field length in such a manner that Category Aone engine inoperative (OEI) climb performance minima can be maintained over a wide range of environmental conditions."
As you can see, maximum permitted VTOSS goes up to 62kt (shouldn't it be 63kt?)
Graphic with ANTI-ICE ON goes up to 63kt.
The second Graphic is first segment climb performance, and there is a 70kt VTOSS on it... but if you use 63kt you will find 34°C, that matches with the second segment climb performance and PC2 maximum takeoff and landing gross weight.
Jim,
I believe that something that can be added to the content is the Operations without an assured safe forced landing capability (OpsSpec H 305?). Could you write something about it?
I found this Advisory Circular from CASA:
https://www.google.com/url?sa=t&rct=...--F1nH32pflzgH
FAA has already authorized Bristow to operate in this manner. Can we consider a breakthrough? Should other countries follow?
https://www.google.com/url?sa=t&rct=...qioq8TNreJjOyc
212man,
"The Category Ahorizontal takeoff procedure shown diagrammatically in Figure 4-7 features variable Takeoff Decision Points (TDP) and Takeoff Safety Speeds (Vtoss). The TDP, expressed only in terms of airspeed, is selectable in 1 knot increments between 30 and 48 knots. Vtoss is TDP + 15 knots. This permits payload to be traded off against available field length in such a manner that Category Aone engine inoperative (OEI) climb performance minima can be maintained over a wide range of environmental conditions."
As you can see, maximum permitted VTOSS goes up to 62kt (shouldn't it be 63kt?)
Graphic with ANTI-ICE ON goes up to 63kt.
The second Graphic is first segment climb performance, and there is a 70kt VTOSS on it... but if you use 63kt you will find 34°C, that matches with the second segment climb performance and PC2 maximum takeoff and landing gross weight.
Last edited by alexandre.vidual; 1st Jun 2023 at 12:22. Reason: add content
The FAA exemption follows the European/ÍCAO model using the graphs provided in Part 2 Section III of the S92 RFM. This originates from the work done on JARs and has been available since the late 90s. It merely allows Bristow to operate as they had previously under other Codes (my guess is that this would be allowed for other applicants).
The AC from CASA is an interpretation of the concepts and text of ICAO Doc 10110 - its contents are well worth reading if you cannot get access to the ICAO Doc.
I haven't read OpsSpec H 305 so cannot comment on its content.
What these references indicate is that most States are now making available the ability to operate in line with the contents of Annex 6, Part III and ICAO Doc 10110 - Helicopter Code of Performance Development Manual; perhaps without actually providing such a code. During the extensive discussions on the subject in the ICAO Helicopter Sub-Group, the FAA representatives always said that, whilst they had filed a difference with ICAO on the contents of Annex 6, Part III, Chapter 3 (i.e. no Code of Performance) because of the difficulty in making changes to the basic regulations, they did regulate through the use of OpsSpecs.
What I previously omitted to mention was that the ICAO based Code of Performance, requires PC1 when more than 19 passengers are carried. The ICAO break points for helicopters are:
PC3 - 9 or fewer
PC2 - 19 or fewer
PC1 - as specified in the Code of Performance or more than 19.
The best document on all of these subjects is ICAO Doc 10110. It may be lengthy but it contains a description of concepts that have been applied world-wide. The only criticism I have of the current document is that it is lacking the comprehensive index it had when it was written, and cross references have been stripped out (navigating in the original was simple). It is not a novel and so should not be read cover-to-cover; it is a reference manual for those trying to understand what a Code of Performance might contain - hence the shame about the lack of an electronic version with cross references.
The AC from CASA is an interpretation of the concepts and text of ICAO Doc 10110 - its contents are well worth reading if you cannot get access to the ICAO Doc.
I haven't read OpsSpec H 305 so cannot comment on its content.
What these references indicate is that most States are now making available the ability to operate in line with the contents of Annex 6, Part III and ICAO Doc 10110 - Helicopter Code of Performance Development Manual; perhaps without actually providing such a code. During the extensive discussions on the subject in the ICAO Helicopter Sub-Group, the FAA representatives always said that, whilst they had filed a difference with ICAO on the contents of Annex 6, Part III, Chapter 3 (i.e. no Code of Performance) because of the difficulty in making changes to the basic regulations, they did regulate through the use of OpsSpecs.
What I previously omitted to mention was that the ICAO based Code of Performance, requires PC1 when more than 19 passengers are carried. The ICAO break points for helicopters are:
PC3 - 9 or fewer
PC2 - 19 or fewer
PC1 - as specified in the Code of Performance or more than 19.
The best document on all of these subjects is ICAO Doc 10110. It may be lengthy but it contains a description of concepts that have been applied world-wide. The only criticism I have of the current document is that it is lacking the comprehensive index it had when it was written, and cross references have been stripped out (navigating in the original was simple). It is not a novel and so should not be read cover-to-cover; it is a reference manual for those trying to understand what a Code of Performance might contain - hence the shame about the lack of an electronic version with cross references.
Last edited by JimL; 3rd Jun 2023 at 05:22.
"The FAA avoids this situation by alleviating from this limitation in FAR 91.9(d) - but only for operations over water." - Same thing here in Brazil.
Jim,
I believe that something that can be added to the content is the Operations without an assured safe forced landing capability (OpsSpec H 305?). Could you write something about it?
I found this Advisory Circular from CASA:
https://www.google.com/url?sa=t&rct=...--F1nH32pflzgH
FAA has already authorized Bristow to operate in this manner. Can we consider a breakthrough? Should other countries follow?
https://www.google.com/url?sa=t&rct=...qioq8TNreJjOyc
212man,
"The Category Ahorizontal takeoff procedure shown diagrammatically in Figure 4-7 features variable Takeoff Decision Points (TDP) and Takeoff Safety Speeds (Vtoss). The TDP, expressed only in terms of airspeed, is selectable in 1 knot increments between 30 and 48 knots. Vtoss is TDP + 15 knots. This permits payload to be traded off against available field length in such a manner that Category Aone engine inoperative (OEI) climb performance minima can be maintained over a wide range of environmental conditions."
As you can see, maximum permitted VTOSS goes up to 62kt (shouldn't it be 63kt?)
Graphic with ANTI-ICE ON goes up to 63kt.
The second Graphic is first segment climb performance, and there is a 70kt VTOSS on it... but if you use 63kt you will find 34°C, that matches with the second segment climb performance and PC2 maximum takeoff and landing gross weight.
Jim,
I believe that something that can be added to the content is the Operations without an assured safe forced landing capability (OpsSpec H 305?). Could you write something about it?
I found this Advisory Circular from CASA:
https://www.google.com/url?sa=t&rct=...--F1nH32pflzgH
FAA has already authorized Bristow to operate in this manner. Can we consider a breakthrough? Should other countries follow?
https://www.google.com/url?sa=t&rct=...qioq8TNreJjOyc
212man,
"The Category Ahorizontal takeoff procedure shown diagrammatically in Figure 4-7 features variable Takeoff Decision Points (TDP) and Takeoff Safety Speeds (Vtoss). The TDP, expressed only in terms of airspeed, is selectable in 1 knot increments between 30 and 48 knots. Vtoss is TDP + 15 knots. This permits payload to be traded off against available field length in such a manner that Category Aone engine inoperative (OEI) climb performance minima can be maintained over a wide range of environmental conditions."
As you can see, maximum permitted VTOSS goes up to 62kt (shouldn't it be 63kt?)
Graphic with ANTI-ICE ON goes up to 63kt.
The second Graphic is first segment climb performance, and there is a 70kt VTOSS on it... but if you use 63kt you will find 34°C, that matches with the second segment climb performance and PC2 maximum takeoff and landing gross weight.
Thread Starter
Thanks for the paper Vidual.
An interesting paper (because it contains a great deal of information - albeit with some small errors and notable omissions) but, in my view, one that reaches the wrong conclusion.
It is unlikely that a Category A procedure for offshore operations (enforced PC1) will ever be practical for a number of reasons - which include: the necessity keep the landing surface in sight during the initial climb manoeuvre (to retain the ability to rejected without damage) and the lack of space to do other than initially to climb vertically - until losing sight of the deck (shown in the 1990s to be about 20ft - which has been stretched by the OEMs to 30ft); the requirement to miss the deck edge by 15ft during the continued take-off; the ability to remain 35ft above the surface of the water in all conditions; the small size of the FATO/TLOF; the 'obstacle environment'/'wind direction' issue; and, finally, the unrealistic expectation that the installed power will ever allow OEI hover performance in zero wind (which is required if PC1 is ever to be enforced).
Jim
An interesting paper (because it contains a great deal of information - albeit with some small errors and notable omissions) but, in my view, one that reaches the wrong conclusion.
It is unlikely that a Category A procedure for offshore operations (enforced PC1) will ever be practical for a number of reasons - which include: the necessity keep the landing surface in sight during the initial climb manoeuvre (to retain the ability to rejected without damage) and the lack of space to do other than initially to climb vertically - until losing sight of the deck (shown in the 1990s to be about 20ft - which has been stretched by the OEMs to 30ft); the requirement to miss the deck edge by 15ft during the continued take-off; the ability to remain 35ft above the surface of the water in all conditions; the small size of the FATO/TLOF; the 'obstacle environment'/'wind direction' issue; and, finally, the unrealistic expectation that the installed power will ever allow OEI hover performance in zero wind (which is required if PC1 is ever to be enforced).
Jim
Almost all these requirements that you mentioned are already fulfilled when we operate Helideck no exposure in the S92. (Clear deck edge by 15ft, water by 35ft and possibility to calculate available droopdown). You can claim that sea state is an issue for the 35ft, but you can easily identify it and add it to the calculation.
The vertical ascent is already performed on CAT A ground level helipad procedure. Situation in which we also lost sight of the landing site when we climbed to TDP (in some situations higher than 100ft). The minimum helipad size limitation for CAT A Ground level helipad is 102 foot square. (I really don't know how anyone manages to reject a takeoff at a height of 100ft, descending vertically, on such a small helipad with a S92).
As for OEI hover performance, would it be IGE or OGE?
Why do helicopters like AW139 have CAT A procedures for elevated helideck in their RFMs?
And why didn't Sikorsky choose to call this procedure as PC2e or to fly test CAT A elevated helideck and put it on RFM part 1, section IV?
Vidual,
I think the point that is important is contained in your first sentence:
The explanation for why PC2e and not Category A is fully explained in Chapter 3.2.4.4 of Doc 10110 (to which you have provided a reference). Here are a couple of extracts:
‘Performance Class 2 enhanced’ (PC2e) is where exposure is present only for a small percentage of flights – i.e. when the helideck environment prevents engine-failure accountability. It requires performance with deck-edge miss and continued flight* following an engine failure on take-off or landing without meeting Category A criteria.
* In the case where flights are being conducted in conditions of low wind and calm seas, operating in ‘pure performance class 2’ would permit a greater take-off mass than PC2e. This would be subject to ‘deck-edge clearance’ assurance and acceptance by the customer that a safe forced landing (ditching) is an acceptable outcome to an engine failure during take-off.
Category A elevated helideck procedures establish profiles and masses (adjusted for wind, temperature and pressure) which assure a 15 ft deck edge clearance on take-off and landing; drop-down must be calculated and, once clear of the helideck, a helicopter operating in PC1 would be expected to meet the 10.7m (35 ft) obstacle clearance (from the sea).
These procedures and clearances can be assured only when: the helideck is of the required size; the take-off or landing is oriented into the obstacle free sector* (OFS); and, the profile is flown as defined. Because these conditions cannot always be fulfilled in offshore operations, a prescriptive regulation requiring operation in PC1 is not regarded as practical (OEI HOGE could be employed but this would result in a severe and unwarranted restriction on payload/range).
* For offshore helidecks, the Obstacle Free Sector (OFS) should extend through a minimum of 210⁰. This consists of a surface clear of obstacles, out to a specified distance, at the helideck level - within which is a 180⁰ arc that is free of obstacles down to sea level (see Annex 14, Volume II, Figures 4-7 and 4-8).
PC2e mass calculation provides notional* performance. Actual performance is dependent upon:
- accuracy of the calculation;
- how close actual conditions are to those planned;
- whether the optimum profile can be flown; and,
- the orientation of the take-off and landing with respect to the OFS.
Planned obstacle clearances should be achieved when the defined profile is flown, and take-off or landing is directly within the OFS; if these conditions cannot be met, exposure might be present**.
* Notional because of the assumption that: the profile is defined and oriented into the OFS; the deck height above sea level is constant; and, the procedure is flown as published.
** Although exposure may only be present for a very small proportion of arrivals/departures, the requirement for PC2e should be contained within a variation that permits exposure.
The text goes on to provide example of when these assurance cannot be met (not shown here). It then continues:
Under these, and other, circumstances, the Commander might adjust the profiles to address a hazard more serious, or more likely, than that presented by an engine failure; regardless of these issues, the calculation of mass should still remain as defined in above.
Because of these, and other (unforeseen) circumstances, a prescriptive requirement for PC2e obstacle clearance cannot be applied*. However, a target of 15 ft deck-edge, and 10.7 m (35 ft) obstacle, clearance should, where possible, be considered.
* If the requirement for PC2e is stated as an objective within a Code of Performance, the method(s) of compliance should specify how the ‘notional’ take-off/landing mass is calculated.
The basis for provision of procedures in Part 2 of the RFMs is provided on the last clause of the referenced text:
This [ed. the procedure] will require manufacturers’ information reflecting these elements. It is expected that such information will be produced by utilising performance modelling/simulation using a model validated through limited flight testing.
The flight testing of a category A procedure is complicated and very expensive - when it is known that it will only be used in principle. It is understood that, for PC2e, manufacturers use their library of flight test data to stitch together a profile (procedure) and then model the outcome to establish it meets the specified clearances. The procedure is put into Part 2 of the RFM which does not require approval by the certificating authority. Although the procedure may well satisfy all the elements of a category A procedure, it cannot be regarded as such.
As this response is getting long, I'll pause and move on to the other points in the next post.
I think the point that is important is contained in your first sentence:
Almost all these requirements that you mentioned are already fulfilled...
‘Performance Class 2 enhanced’ (PC2e) is where exposure is present only for a small percentage of flights – i.e. when the helideck environment prevents engine-failure accountability. It requires performance with deck-edge miss and continued flight* following an engine failure on take-off or landing without meeting Category A criteria.
* In the case where flights are being conducted in conditions of low wind and calm seas, operating in ‘pure performance class 2’ would permit a greater take-off mass than PC2e. This would be subject to ‘deck-edge clearance’ assurance and acceptance by the customer that a safe forced landing (ditching) is an acceptable outcome to an engine failure during take-off.
Category A elevated helideck procedures establish profiles and masses (adjusted for wind, temperature and pressure) which assure a 15 ft deck edge clearance on take-off and landing; drop-down must be calculated and, once clear of the helideck, a helicopter operating in PC1 would be expected to meet the 10.7m (35 ft) obstacle clearance (from the sea).
These procedures and clearances can be assured only when: the helideck is of the required size; the take-off or landing is oriented into the obstacle free sector* (OFS); and, the profile is flown as defined. Because these conditions cannot always be fulfilled in offshore operations, a prescriptive regulation requiring operation in PC1 is not regarded as practical (OEI HOGE could be employed but this would result in a severe and unwarranted restriction on payload/range).
* For offshore helidecks, the Obstacle Free Sector (OFS) should extend through a minimum of 210⁰. This consists of a surface clear of obstacles, out to a specified distance, at the helideck level - within which is a 180⁰ arc that is free of obstacles down to sea level (see Annex 14, Volume II, Figures 4-7 and 4-8).
PC2e mass calculation provides notional* performance. Actual performance is dependent upon:
- accuracy of the calculation;
- how close actual conditions are to those planned;
- whether the optimum profile can be flown; and,
- the orientation of the take-off and landing with respect to the OFS.
Planned obstacle clearances should be achieved when the defined profile is flown, and take-off or landing is directly within the OFS; if these conditions cannot be met, exposure might be present**.
* Notional because of the assumption that: the profile is defined and oriented into the OFS; the deck height above sea level is constant; and, the procedure is flown as published.
** Although exposure may only be present for a very small proportion of arrivals/departures, the requirement for PC2e should be contained within a variation that permits exposure.
The text goes on to provide example of when these assurance cannot be met (not shown here). It then continues:
Under these, and other, circumstances, the Commander might adjust the profiles to address a hazard more serious, or more likely, than that presented by an engine failure; regardless of these issues, the calculation of mass should still remain as defined in above.
Because of these, and other (unforeseen) circumstances, a prescriptive requirement for PC2e obstacle clearance cannot be applied*. However, a target of 15 ft deck-edge, and 10.7 m (35 ft) obstacle, clearance should, where possible, be considered.
* If the requirement for PC2e is stated as an objective within a Code of Performance, the method(s) of compliance should specify how the ‘notional’ take-off/landing mass is calculated.
The basis for provision of procedures in Part 2 of the RFMs is provided on the last clause of the referenced text:
This [ed. the procedure] will require manufacturers’ information reflecting these elements. It is expected that such information will be produced by utilising performance modelling/simulation using a model validated through limited flight testing.
The flight testing of a category A procedure is complicated and very expensive - when it is known that it will only be used in principle. It is understood that, for PC2e, manufacturers use their library of flight test data to stitch together a profile (procedure) and then model the outcome to establish it meets the specified clearances. The procedure is put into Part 2 of the RFM which does not require approval by the certificating authority. Although the procedure may well satisfy all the elements of a category A procedure, it cannot be regarded as such.
As this response is getting long, I'll pause and move on to the other points in the next post.
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Vidual,
The helipad procedure has distinct advantages with respect to lateral visual cues. It is stated in AC 29-2C that two sides of the helipad should be in sight during the vertical ascent (however, it is only guidance material). It is noted that you quote a minimum ground level helipad size of 210 ft = 31 m; with lateral visual cues, that allows some leeway.
The surface of helidecks world-wide are generally built for a design D of 22m (the D of the S61). It was shown (in trials with the S61N in the early 90s) that with a deck of this size, visual reference is lost at about 20 ft. From that point pilots (inadvertently) start to drift backward to maintain visual reference. (Experienced offshore pilots almost always take their reference from the obstacles within the 150 degree sector at the side of the helicopter - this prevents a backward drift.)
In the referenced material OEI OGE is stated.
When the AW139 was certificated it was a helicopter with very good installed power. It could provide helideck Category A performance (meeting the 15 ft deck-edge clearance) within a TDP of 30 ft at maximum mass. In fact in most cases, there would be no drop down below the deck and min dip was well ahead of the rig. Weight growth has gradually eroded that power reserve. Because of this installed power, there was little (financial or operational) risk in an offshore trial leading to certification in Category A for this procedure. It would prove to be a very sound decision.
Even so, there would be occasions when the profile could not be flown (e.g. wind through the derick outside the cross-wind limits). As is stated in the Doc 10110 text:
Under these [ed. provided in the reference], and other, circumstances, the Commander might adjust the profiles to address a hazard more serious, or more likely, than that presented by an engine failure; regardless of these issues, the calculation of mass should still remain as defined in above.
The pilot would then have to revert to using it as PC2e - if within the operational approval.
As for the S92 nomenclature, I think this was originally the case but, for political/commercial reasons, it was changed. The reasons for not running an offshore flight testing regime and seeking approval were discussed above. The S76 approval flight trials took months and imposed a huge administrative/logistical/financial burden on the company - my guess is that Sikorsky, in concert with other manufacturers, took the view that a Category A helideck procedure would never be forced upon them. (The experience with the limited provision of S76 modification kits, that were required to apply the Category A procedure, probably showed that the uptake of the procedure was, in fact, limited in nature.)
The helipad procedure has distinct advantages with respect to lateral visual cues. It is stated in AC 29-2C that two sides of the helipad should be in sight during the vertical ascent (however, it is only guidance material). It is noted that you quote a minimum ground level helipad size of 210 ft = 31 m; with lateral visual cues, that allows some leeway.
The surface of helidecks world-wide are generally built for a design D of 22m (the D of the S61). It was shown (in trials with the S61N in the early 90s) that with a deck of this size, visual reference is lost at about 20 ft. From that point pilots (inadvertently) start to drift backward to maintain visual reference. (Experienced offshore pilots almost always take their reference from the obstacles within the 150 degree sector at the side of the helicopter - this prevents a backward drift.)
In the referenced material OEI OGE is stated.
When the AW139 was certificated it was a helicopter with very good installed power. It could provide helideck Category A performance (meeting the 15 ft deck-edge clearance) within a TDP of 30 ft at maximum mass. In fact in most cases, there would be no drop down below the deck and min dip was well ahead of the rig. Weight growth has gradually eroded that power reserve. Because of this installed power, there was little (financial or operational) risk in an offshore trial leading to certification in Category A for this procedure. It would prove to be a very sound decision.
Even so, there would be occasions when the profile could not be flown (e.g. wind through the derick outside the cross-wind limits). As is stated in the Doc 10110 text:
Under these [ed. provided in the reference], and other, circumstances, the Commander might adjust the profiles to address a hazard more serious, or more likely, than that presented by an engine failure; regardless of these issues, the calculation of mass should still remain as defined in above.
The pilot would then have to revert to using it as PC2e - if within the operational approval.
As for the S92 nomenclature, I think this was originally the case but, for political/commercial reasons, it was changed. The reasons for not running an offshore flight testing regime and seeking approval were discussed above. The S76 approval flight trials took months and imposed a huge administrative/logistical/financial burden on the company - my guess is that Sikorsky, in concert with other manufacturers, took the view that a Category A helideck procedure would never be forced upon them. (The experience with the limited provision of S76 modification kits, that were required to apply the Category A procedure, probably showed that the uptake of the procedure was, in fact, limited in nature.)
Last edited by JimL; 5th Jun 2023 at 12:25.
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Thread Starter
Thanks Jim,
I'll leave a link to a performance-related crash.
Mi-172 Crash
You don't need to lose an engine to have to correctly calculate the available performance for each flight, how many times do we neglect this planning?
Today we have tablet and mobile apps that quickly give us the numbers we need to know. Everything has become much easier, we just need to realize how important this is for our flight and how much it can help us make the right decisions.
fly safe
I'll leave a link to a performance-related crash.
Mi-172 Crash
You don't need to lose an engine to have to correctly calculate the available performance for each flight, how many times do we neglect this planning?
Today we have tablet and mobile apps that quickly give us the numbers we need to know. Everything has become much easier, we just need to realize how important this is for our flight and how much it can help us make the right decisions.
fly safe
Last edited by alexandre.vidual; 5th Jun 2023 at 19:26.
That article in Vertical by KP Sanjeev Kumar (referred to by Vidual), is extremely well written and easy to follow. At the end is contained a pointer to - 'Reject or Continue? Understanding Category A Performance' - another written by KP. There are some small errors in both but he has the ability to capture his reader.
Have you ever pondered over the relevance of the two minimum climb standards - first segment 100ft/min and second segment 150ft/min to the operating environment. Well, very little.
During the provision and amendment of Part 29 (the certification code which contains the provisions for certification in Category A) it was proposed that minimum gradients should be specified. Some parties contended that only a minimum climb standard should be specified (that contained in 29.67) with the gradient data provided as information - specified in 29.1587 as the provision of:
"The steady gradient of climb for each weight, altitude, and temperature for which take-off data are to be scheduled..."
It is this data that relates to the operating environment; it is provided (as in the S92A manual) as graphs showing:
"Mean height gained in 100ft horizontal distance applicable ..."
i.e. to: (1) the specified Vtoss applicable from 35ft - 200ft; or (2) the best rate of climb speed (BROC) applicable from 200ft - 1000ft, (both adjusted for installed equipment - i.e. anti-ice, air conditioner etc.). This is effectively shown as a percentage - i.e. height gained in feet/100.
These gradients can be related to the heliport data - for example the gradient of the take-off 'design slope category A', is 4.5% (also shown as a ratio of 1:22.2) providing an angle of 2.58 degrees.
The pilot is now able to relate the data i.e. rejected take-off distance (to the length of the FATO), take-off distance required (to the length of the FATO plus any clearway), and climb gradient (the gradient of the take-off surface), to heliport information and obstacle data.
Far from the steep slopes that are usually shown in RFM or presentation diagrams (of which I am myself guilty), a 100ft/min climb at a Vtoss of 60kts in ISA conditions provides (only) a gradient of 1.6% or climb angle of about 0.9 degrees.
Not exactly 'Formula 1' stuff is it?
Have you ever pondered over the relevance of the two minimum climb standards - first segment 100ft/min and second segment 150ft/min to the operating environment. Well, very little.
During the provision and amendment of Part 29 (the certification code which contains the provisions for certification in Category A) it was proposed that minimum gradients should be specified. Some parties contended that only a minimum climb standard should be specified (that contained in 29.67) with the gradient data provided as information - specified in 29.1587 as the provision of:
"The steady gradient of climb for each weight, altitude, and temperature for which take-off data are to be scheduled..."
It is this data that relates to the operating environment; it is provided (as in the S92A manual) as graphs showing:
"Mean height gained in 100ft horizontal distance applicable ..."
i.e. to: (1) the specified Vtoss applicable from 35ft - 200ft; or (2) the best rate of climb speed (BROC) applicable from 200ft - 1000ft, (both adjusted for installed equipment - i.e. anti-ice, air conditioner etc.). This is effectively shown as a percentage - i.e. height gained in feet/100.
These gradients can be related to the heliport data - for example the gradient of the take-off 'design slope category A', is 4.5% (also shown as a ratio of 1:22.2) providing an angle of 2.58 degrees.
The pilot is now able to relate the data i.e. rejected take-off distance (to the length of the FATO), take-off distance required (to the length of the FATO plus any clearway), and climb gradient (the gradient of the take-off surface), to heliport information and obstacle data.
Far from the steep slopes that are usually shown in RFM or presentation diagrams (of which I am myself guilty), a 100ft/min climb at a Vtoss of 60kts in ISA conditions provides (only) a gradient of 1.6% or climb angle of about 0.9 degrees.
Not exactly 'Formula 1' stuff is it?
Thread Starter
Jim,
If the minimum required performance standard cannot immediately cope (because of the shallow gradients) with runway-type sites, how can PC1 operations to a ground level or elevated helipad be
conducted?
Regards,
Vidual
If the minimum required performance standard cannot immediately cope (because of the shallow gradients) with runway-type sites, how can PC1 operations to a ground level or elevated helipad be
conducted?
Regards,
Vidual
Meeting the minimum certification standard does not, in itself, provide any capability other than allowing compliance with the limitations of the RFM. It is the operations manual that needs to specify the performance standard for PC1 – normally, in conformance with a State’s Code of Performance.
(Depending on the speed specified for the type/procedure, the minimum required performance for the first segment might only provide a climb gradient of 1.6% or 0.9°- which is almost indistinguishable from level flight. Minimum performance in the second segment is almost as bad at 1.8% or 1.06°. The shallowest available slope at a PC1 heliport is 4.5% or 2.58°.)
It should therefore be clear that minimum Category A performance standards are not, in themselves, sufficient to provide obstacle clearance; that is why, in many performance presentations, it is stated that PC1 is a Category A procedure plus application of (obstacle) clearance to the local environment.
Minimum Category A climb performance is not really applicable to any known obstacle environment, it is performance in a semantic bubble. This is not just true of helipads, it also applies to runway-type heliports.
It is only possible to take-off in PC1 from a heliport when the following are known and/or accounted for (or standard company procedures assuring obstacle clearance are in place):
For a runway procedure: the rejected distance, continued take-off distance (which may, or may not, include a clearway), and take-off climb slope;
For a helipad procedure (including one within a limited area): the size of the helipad surface (for reject), the elevation and dimension of the clearway, and take-off climb slope;
Whatever profile is used, two things are necessary (which are in themselves obvious): (1) when flying to the TDP it must be possible to keep the rejected area in sight at all times; and (2), sufficient space must be available to allow the rotorcraft to accelerate from TDP to Vtoss prior to commencing the initial climb.
For other than a runway-type procedure, (2) above will inevitably require a vertical procedure where completion of the acceleration to Vtoss is conducted outside the boundary of the heliport - in most cases over obstacles.
In order for the pilot to ensure that min-dip remains (the required height) above obstacles in the continued take-off, the provision of an elevated clearway is necessary. The elevated clearway provides: a level datum for establishing the height of the TDP, at a length sufficient to allow completion of the acceleration to Vtoss.
For those who have not read the whole thread, here is a pointer to a number of slides that illustrate the above:
https://www.dropbox.com/s/i5am5zyg5a...sion.pptx?dl=0
The required procedure will be found in the Category A supplement; the take-off mass should, as well meeting the WAT, allow the required climb gradient (normally 4.5%) throughout the first, level and second segments (as constructed in the RFM supplement).
Almost all modern helicopters provide a suite of Category A (vertical) procedures; most can achieve take-off at a practical operating mass even when the clearway is elevated to a substantial height above the take-off surface (to raise it, and the take-off climb surface, above all obstacles). Power reserve provided by the 30 second and 2 minute settings (or 2.5 minutes if no 30 second setting is stipulated) can provide access to heliports (and required climb performance) in even the most complex obstacle environment (i.e. city centres with high rise buildings).
(Depending on the speed specified for the type/procedure, the minimum required performance for the first segment might only provide a climb gradient of 1.6% or 0.9°- which is almost indistinguishable from level flight. Minimum performance in the second segment is almost as bad at 1.8% or 1.06°. The shallowest available slope at a PC1 heliport is 4.5% or 2.58°.)
It should therefore be clear that minimum Category A performance standards are not, in themselves, sufficient to provide obstacle clearance; that is why, in many performance presentations, it is stated that PC1 is a Category A procedure plus application of (obstacle) clearance to the local environment.
Minimum Category A climb performance is not really applicable to any known obstacle environment, it is performance in a semantic bubble. This is not just true of helipads, it also applies to runway-type heliports.
It is only possible to take-off in PC1 from a heliport when the following are known and/or accounted for (or standard company procedures assuring obstacle clearance are in place):
For a runway procedure: the rejected distance, continued take-off distance (which may, or may not, include a clearway), and take-off climb slope;
For a helipad procedure (including one within a limited area): the size of the helipad surface (for reject), the elevation and dimension of the clearway, and take-off climb slope;
Whatever profile is used, two things are necessary (which are in themselves obvious): (1) when flying to the TDP it must be possible to keep the rejected area in sight at all times; and (2), sufficient space must be available to allow the rotorcraft to accelerate from TDP to Vtoss prior to commencing the initial climb.
For other than a runway-type procedure, (2) above will inevitably require a vertical procedure where completion of the acceleration to Vtoss is conducted outside the boundary of the heliport - in most cases over obstacles.
In order for the pilot to ensure that min-dip remains (the required height) above obstacles in the continued take-off, the provision of an elevated clearway is necessary. The elevated clearway provides: a level datum for establishing the height of the TDP, at a length sufficient to allow completion of the acceleration to Vtoss.
For those who have not read the whole thread, here is a pointer to a number of slides that illustrate the above:
https://www.dropbox.com/s/i5am5zyg5a...sion.pptx?dl=0
The required procedure will be found in the Category A supplement; the take-off mass should, as well meeting the WAT, allow the required climb gradient (normally 4.5%) throughout the first, level and second segments (as constructed in the RFM supplement).
Almost all modern helicopters provide a suite of Category A (vertical) procedures; most can achieve take-off at a practical operating mass even when the clearway is elevated to a substantial height above the take-off surface (to raise it, and the take-off climb surface, above all obstacles). Power reserve provided by the 30 second and 2 minute settings (or 2.5 minutes if no 30 second setting is stipulated) can provide access to heliports (and required climb performance) in even the most complex obstacle environment (i.e. city centres with high rise buildings).
A number of my colleagues having seen this thread unfold, have expressed a view that the understanding of some of the issues would be enhanced with a simple guide (not necessarily referenced based but a personal and historical view) with less emphasis on the Performance Classes for those States in which they are not, necessarily, mandated.
This has been done and it is referenced below in its latest iteration:
The introduction and evolution of Category A procedures - from runways to heliports in city centres
It provides a view of the introduction and evolution of Category A procedures and their progression from the original intent to mirror those of fixed-wing, to their use on small sites and city centres - both at ground level and elevated. It leans heavily on the recent work of the Heliport Design Committee on the ICAO Heliport Manual (ICAO Doc 9261) and goes beyond the contents of the ICAO Performance Manual (ICAO Doc 10110).
Some of the techniques are not yet in use as ICAO Standards but are expected to be in the near future. The more interesting parts - for pilots who follow the development of hospital sites and their required procedures - will be familiar, if only because they reflect the continuing development of Category A supplements for use in HEMS operations - mostly in Europe but also those States for which the risk to third parties (property as well as persons) is mandated in regulations.
As usual, your comments are welcome.
This has been done and it is referenced below in its latest iteration:
The introduction and evolution of Category A procedures - from runways to heliports in city centres
It provides a view of the introduction and evolution of Category A procedures and their progression from the original intent to mirror those of fixed-wing, to their use on small sites and city centres - both at ground level and elevated. It leans heavily on the recent work of the Heliport Design Committee on the ICAO Heliport Manual (ICAO Doc 9261) and goes beyond the contents of the ICAO Performance Manual (ICAO Doc 10110).
Some of the techniques are not yet in use as ICAO Standards but are expected to be in the near future. The more interesting parts - for pilots who follow the development of hospital sites and their required procedures - will be familiar, if only because they reflect the continuing development of Category A supplements for use in HEMS operations - mostly in Europe but also those States for which the risk to third parties (property as well as persons) is mandated in regulations.
As usual, your comments are welcome.
The following users liked this post:
A number of my colleagues having seen this thread unfold, have expressed a view that the understanding of some of the issues would be enhanced with a simple guide (not necessarily referenced based but a personal and historical view) with less emphasis on the Performance Classes for those States in which they are not, necessarily, mandated.
This has been done and it is referenced below in its latest iteration:
The introduction and evolution of Category A procedures - from runways to heliports in city centres
It provides a view of the introduction and evolution of Category A procedures and their progression from the original intent to mirror those of fixed-wing, to their use on small sites and city centres - both at ground level and elevated. It leans heavily on the recent work of the Heliport Design Committee on the ICAO Heliport Manual (ICAO Doc 9261) and goes beyond the contents of the ICAO Performance Manual (ICAO Doc 10110).
Some of the techniques are not yet in use as ICAO Standards but are expected to be in the near future. The more interesting parts - for pilots who follow the development of hospital sites and their required procedures - will be familiar, if only because they reflect the continuing development of Category A supplements for use in HEMS operations - mostly in Europe but also those States for which the risk to third parties (property as well as persons) is mandated in regulations.
As usual, your comments are welcome.
This has been done and it is referenced below in its latest iteration:
The introduction and evolution of Category A procedures - from runways to heliports in city centres
It provides a view of the introduction and evolution of Category A procedures and their progression from the original intent to mirror those of fixed-wing, to their use on small sites and city centres - both at ground level and elevated. It leans heavily on the recent work of the Heliport Design Committee on the ICAO Heliport Manual (ICAO Doc 9261) and goes beyond the contents of the ICAO Performance Manual (ICAO Doc 10110).
Some of the techniques are not yet in use as ICAO Standards but are expected to be in the near future. The more interesting parts - for pilots who follow the development of hospital sites and their required procedures - will be familiar, if only because they reflect the continuing development of Category A supplements for use in HEMS operations - mostly in Europe but also those States for which the risk to third parties (property as well as persons) is mandated in regulations.
As usual, your comments are welcome.
The following users liked this post:
Since putting this document up on the board, there have been a number of suggestions for improving its comprehension - they have been accepted. However, as always, the responsibility for all faults remain with me.
The changes have been made in situ but, if you have already downloaded the document to pass to colleagues, please pick it up again. The link continues to work with the revised text.
Enjoy.
The changes have been made in situ but, if you have already downloaded the document to pass to colleagues, please pick it up again. The link continues to work with the revised text.
Enjoy.