Multi Engine Helicopters & the HV Curve
Shawn,
Whilst your statement is true in the sense of basic certification (29.1), it would have to have been certificated with 9 or less seats. That would be rather unusual; for that reason, the overwhelming majority (in fact I cannot think of any to which it doesn't apply) of Part 29 helicopters have the HV diagram in their FM limitations section.
As Hullaballo has already pointed out, the majority of operations with Part 29 helicopters do not operate in PC1 using the CAT A procedures. In fact for offshore operations, none of them do. It is only because of the relief from the HV diagram provided by FAR 91.9(d) and Appendix 1 to JAR-OPS 3.005(c) that they are able to stay legal (and it is not clear how that plays out in States with other regulations).
For onshore operations, JARs have relief but not FARs!
Jim
Whilst your statement is true in the sense of basic certification (29.1), it would have to have been certificated with 9 or less seats. That would be rather unusual; for that reason, the overwhelming majority (in fact I cannot think of any to which it doesn't apply) of Part 29 helicopters have the HV diagram in their FM limitations section.
As Hullaballo has already pointed out, the majority of operations with Part 29 helicopters do not operate in PC1 using the CAT A procedures. In fact for offshore operations, none of them do. It is only because of the relief from the HV diagram provided by FAR 91.9(d) and Appendix 1 to JAR-OPS 3.005(c) that they are able to stay legal (and it is not clear how that plays out in States with other regulations).
For onshore operations, JARs have relief but not FARs!
Jim
Last edited by JimL; 1st Jul 2009 at 16:50.
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It's comparing apples and oranges because of the differences in testing and delivery requirements, but if Nick goes to the Tech Pub library at his current employer and pulls the AH-1W NATOPS manual, he'll see a very useful chart (two charts actually) that provide the minimum hover height and airspeed for a safe OEI landing at a range of density altitudes and gross weights. We understood a "safe landing" as to be one which would result in no injury and minimal aircraft damage.
When I was working as a TP at Pax River on the H-1 program, we had a well defined test process (as did Bell) to develop and test these numbers. To be clear, we verified manufacturer numbers, Bell developed them.
The information was useful, though due to airspeed indicator unreliability below 40 knots, the minimum airspeed number was advisory at best. The ground speed indicator and maintaining an awareness of wind direction was of some help.
There is no reason other than liability concern that prevents manufacturers from providing this data to dual engine helicopter pilots.
When I was working as a TP at Pax River on the H-1 program, we had a well defined test process (as did Bell) to develop and test these numbers. To be clear, we verified manufacturer numbers, Bell developed them.
The information was useful, though due to airspeed indicator unreliability below 40 knots, the minimum airspeed number was advisory at best. The ground speed indicator and maintaining an awareness of wind direction was of some help.
There is no reason other than liability concern that prevents manufacturers from providing this data to dual engine helicopter pilots.
There is no reason other than liability concern that prevents manufacturers from providing this data to dual engine helicopter pilots.
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Multi Engine Helicopters & the HV Curve
Shawn Coyle in his book titled "Cyclic & Collective" on page 338 details an interesting fact about Civil helicopters over 6000Lbs, certified under Part 29, Transport Category with more than 9 passengers ie S76, AS365, B412 etc.
The HV curve is placed in the LIMITATIONS section of the flight manual.
Therefore, conducting a vertical climb for takeoff procedure eg from a confined area (as detailed in the CAT A Supplement) is violating a Flight Manual limitation unless the helicopter is operating at or below the CAT A performance weights.
Exemption
HEMS helicopters however can be exempt from this limitation as they carry less than 9 persons, however a Flight Manual Supplement must be approved by the FAA/CAA for their Air Ambulance Operation.
Does anyone have one of these FM Supplements in their flight manual and are able to email me a PDF copy?
The HV curve is placed in the LIMITATIONS section of the flight manual.
Therefore, conducting a vertical climb for takeoff procedure eg from a confined area (as detailed in the CAT A Supplement) is violating a Flight Manual limitation unless the helicopter is operating at or below the CAT A performance weights.
Exemption
HEMS helicopters however can be exempt from this limitation as they carry less than 9 persons, however a Flight Manual Supplement must be approved by the FAA/CAA for their Air Ambulance Operation.
Does anyone have one of these FM Supplements in their flight manual and are able to email me a PDF copy?
...don't forget the alleviations from the HV curve contained in FAR 91.9(c) and Appendix 1 to JAR-OPS 3.005(c).
Attempting to regulate operations from inside Part 29 was always an unrealistic proposition. This has been recognised for some time but still results in a head-in-the-sand attitude by some regulators. (Explain to me how offshore operations can be conducted in the GOM without breaching this limitation - not just for the helicopters mentioned but also for the S92 and EC225.)
Fortunately there is a move by EASA to resolve this (at least for Europe); they have it on their work programme to be addressed before EASA OPS comes into effect.
The masses have changed in recent years - the break between Part 27 and 27 is now 7,000lbs not 6,000lbs.
Jim
Attempting to regulate operations from inside Part 29 was always an unrealistic proposition. This has been recognised for some time but still results in a head-in-the-sand attitude by some regulators. (Explain to me how offshore operations can be conducted in the GOM without breaching this limitation - not just for the helicopters mentioned but also for the S92 and EC225.)
Fortunately there is a move by EASA to resolve this (at least for Europe); they have it on their work programme to be addressed before EASA OPS comes into effect.
The masses have changed in recent years - the break between Part 27 and 27 is now 7,000lbs not 6,000lbs.
Jim
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...don't forget the alleviations from the HV curve contained in FAR 91.9(c) and Appendix 1 to JAR-OPS 3.005(c).
Fortunately there is a move by EASA to resolve this (at least for Europe); they have it on their work programme to be addressed before EASA OPS comes into effect.
HeliTester,
Yes, the issue needs to be addressed in a more general form than the two alleviations shown (which are under scrutiny because they both contradict the Flight Manual).
The move to introduce exposure into the regulations (and subsequently into the ICAO SARPs) brought this into focus some years ago. The alleviation was seen as sufficient to address the operational necessity to have the required flexibility. Even though the European alleviation was comprehensive, the FAA one wasn't (addressing only over-water departures).
The move to put the European Regulations onto a more legal footing has now resulted in a reluctance to continue with the current rule alleviation and a more permanent solution is being sought (hence the move to remove the HV diagram from the limitation section).
There is no problem for HEMS, or any other operation permitting exposure during the take-off and landing phases. AL 5 introduced ground level exposure, which provided the additional flexibility that was omitted (deliberately) from NP 8. Exposure is now permitted in all but a congested hostile environment; for the HEMS Operating Site this is also permitted. HEMS locations (hospitals) in a congested hostile environment (other than a HEMS Operating Base) are addressed by the Public Interest Site provisions. This is unlikely to change with EASA OPS.
The (apparent) provisions of FAR 29.1 and the inclusion of the HV diagram in the Limitations Section can confine a Part 29 helicopter to operations in Performance Class 1 (using a CAT A procedure). The fact that Europe has a slightly different slant on the interpretation of Part 29.1 is mainly because the definition of CAT A differs between the FAA and Europe (ICAO appears to favour the European position). In the European definition the performance data that is provided in compliance with Part 29 is seen as facilitating the use of PC1, not requiring it.
Jim
Yes, the issue needs to be addressed in a more general form than the two alleviations shown (which are under scrutiny because they both contradict the Flight Manual).
The move to introduce exposure into the regulations (and subsequently into the ICAO SARPs) brought this into focus some years ago. The alleviation was seen as sufficient to address the operational necessity to have the required flexibility. Even though the European alleviation was comprehensive, the FAA one wasn't (addressing only over-water departures).
The move to put the European Regulations onto a more legal footing has now resulted in a reluctance to continue with the current rule alleviation and a more permanent solution is being sought (hence the move to remove the HV diagram from the limitation section).
There is no problem for HEMS, or any other operation permitting exposure during the take-off and landing phases. AL 5 introduced ground level exposure, which provided the additional flexibility that was omitted (deliberately) from NP 8. Exposure is now permitted in all but a congested hostile environment; for the HEMS Operating Site this is also permitted. HEMS locations (hospitals) in a congested hostile environment (other than a HEMS Operating Base) are addressed by the Public Interest Site provisions. This is unlikely to change with EASA OPS.
The (apparent) provisions of FAR 29.1 and the inclusion of the HV diagram in the Limitations Section can confine a Part 29 helicopter to operations in Performance Class 1 (using a CAT A procedure). The fact that Europe has a slightly different slant on the interpretation of Part 29.1 is mainly because the definition of CAT A differs between the FAA and Europe (ICAO appears to favour the European position). In the European definition the performance data that is provided in compliance with Part 29 is seen as facilitating the use of PC1, not requiring it.
Jim
Last edited by JimL; 10th Sep 2010 at 09:24.
It would also help if the HV data was more comprehensive to allow more precise determination of when it is actually extant. The Bell 212 had this over 30 years ago - it's a shame that most current RFMs have such a simplistic indication.
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212man,
I am familiar with the more comprehensive H-V diagrams to which you refer. Figure AC 29.79-2 shows three different ways to present H-V data, the most simplistic of which is the one commonly used today where the H-V avoid area is fixed and accommodates all gross weight/density altitude conditions at up to the HOGE weight (for all altitudes and temperatures within the certification envelope).
I understand your desire for a more precise determination of the H-V avoid area. But H-V testing is a risky business, and one could argue that exposing the test aircraft and crew to the number of engine cuts necessary to develop a more comprehensive H-V diagram is not worth the risk. It is my observation that more parts are bent during H-V testing than during structural demonstration testing, including hard landing tests where the aircraft is flown into the ground at a pre-determined airspeed and ROD.
HT
I am familiar with the more comprehensive H-V diagrams to which you refer. Figure AC 29.79-2 shows three different ways to present H-V data, the most simplistic of which is the one commonly used today where the H-V avoid area is fixed and accommodates all gross weight/density altitude conditions at up to the HOGE weight (for all altitudes and temperatures within the certification envelope).
I understand your desire for a more precise determination of the H-V avoid area. But H-V testing is a risky business, and one could argue that exposing the test aircraft and crew to the number of engine cuts necessary to develop a more comprehensive H-V diagram is not worth the risk. It is my observation that more parts are bent during H-V testing than during structural demonstration testing, including hard landing tests where the aircraft is flown into the ground at a pre-determined airspeed and ROD.
HT
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Gents,
I know this is a very old thread, but it seems that there's plenty of misinterpretations in my current field of operation - off-shore and seemingly in other fields too.
Cat A and Cat B are design and build certification requirements - correct. The manufacturers will tick the boxes as laid down to certify the Cat A and B requirements. This will be i the form of Profiles, Performance Charts and Emergency Procedures. Ultimately the aircraft is certified to use the Cat A and Cat B procedures as published. How the aircraft is "Operated" then becomes a matter of Performance Classes. This will be dictated by the area of operation and the level of risk that the client or operator is prepared to accept. The considerations would be take off/landing environment, surface as well as the relevant altitude and temperatures.
Some articles and threads I've read recently state that Cat A Profiles assure that the H/V Areas will be avoided. I thought that this was only the case for the Cat B profiles? Cat A assures the OEi capability, and Cat B assures the Cat B profile will keep you out of the H/V Curve.
Surely the H/V Diagrams are only concerned with Auto-rotational landings - hence engine failure in a single engine helicopter and double engine failure in a twin ?
Cat A Profiles and Emergency Procedures are only concerned with OEi accountability - correct? And thus there will be Cat A profiles that do put the helicopter squarely inside the H/V Curves in many cases
I'm listening for your inputs and insight
Respectfully
I know this is a very old thread, but it seems that there's plenty of misinterpretations in my current field of operation - off-shore and seemingly in other fields too.
Cat A and Cat B are design and build certification requirements - correct. The manufacturers will tick the boxes as laid down to certify the Cat A and B requirements. This will be i the form of Profiles, Performance Charts and Emergency Procedures. Ultimately the aircraft is certified to use the Cat A and Cat B procedures as published. How the aircraft is "Operated" then becomes a matter of Performance Classes. This will be dictated by the area of operation and the level of risk that the client or operator is prepared to accept. The considerations would be take off/landing environment, surface as well as the relevant altitude and temperatures.
Some articles and threads I've read recently state that Cat A Profiles assure that the H/V Areas will be avoided. I thought that this was only the case for the Cat B profiles? Cat A assures the OEi capability, and Cat B assures the Cat B profile will keep you out of the H/V Curve.
Surely the H/V Diagrams are only concerned with Auto-rotational landings - hence engine failure in a single engine helicopter and double engine failure in a twin ?
Cat A Profiles and Emergency Procedures are only concerned with OEi accountability - correct? And thus there will be Cat A profiles that do put the helicopter squarely inside the H/V Curves in many cases
I'm listening for your inputs and insight
Respectfully
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Flexshaft, basically no.
The ME avoid curve is derived from the H/V combination where a safe landing is not assured after losing one engine. I.e going from AEO to OEI. Nothing to do with autorotations.
Due to various torque/engine/pilot limitations you are not necessarily "safe single engine" in all phases of twin-engine flight.
As an example the Lynx which I flew typically had a minimum single engine level flight speed (MSELFS) of 0-50kts, depending on the environmental conditions and AUM. Flying below this speed at an altitude which did not allow a descent to increase speed to recover is inside the twin HV curve.
Hope this helps.
The ME avoid curve is derived from the H/V combination where a safe landing is not assured after losing one engine. I.e going from AEO to OEI. Nothing to do with autorotations.
Due to various torque/engine/pilot limitations you are not necessarily "safe single engine" in all phases of twin-engine flight.
As an example the Lynx which I flew typically had a minimum single engine level flight speed (MSELFS) of 0-50kts, depending on the environmental conditions and AUM. Flying below this speed at an altitude which did not allow a descent to increase speed to recover is inside the twin HV curve.
Hope this helps.
As Katfish says, you don't have to have an engine failure to end up on one engine: engine chip, false fire warning, loss of oil pressure, are all events I've seen in the recent past.
How many Engine Chip lights preceded an actual engine failure?
If Brother Lappos thinks we worry about a mere 5%.....I would submit that worrying about an Engine Chip Light being any kind of warning that requires any sort of immediate action beyond re-setting the Master Caution Light then monitoring some instruments and listening for abnormalities..... is really over the top.
I guess some folks whistle as they walk by a cemetery at night too thinking that helps keep the Haints away.
I would submit that worrying about an Engine Chip Light being any kind of warning that requires any sort of immediate action beyond re-setting the Master Caution Light then monitoring some instruments and listening for abnormalities..... is really over the top
Did a US Army accident course at Headshed Vietnam and they showed an interesting video of the establishment of the zero airspeed line of the OH6 HV curve. Started high and worked his way down in altitude, you could see things were getting progressively more exciting, the final rolling into a ball and coming to rest on its side. Driver climbed out unscathed, turned, looked at the wreck, removed helmet and threw it at the comatose Hughes.
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Interesting Thread.
My old and wise instructor told me that the H/V curve in a CAT A certified machine was only associated with the clear area T/O and landing profiles.
It is not relevant to VTOL procedures for obvious reasons.
And applys to all CAT B operations. It applys to clear area PC 1 and PC2 as it’s only the TDP and LDP points that change.
I am sure I will get some feed back on these thoughts.
My old and wise instructor told me that the H/V curve in a CAT A certified machine was only associated with the clear area T/O and landing profiles.
It is not relevant to VTOL procedures for obvious reasons.
And applys to all CAT B operations. It applys to clear area PC 1 and PC2 as it’s only the TDP and LDP points that change.
I am sure I will get some feed back on these thoughts.
Flexshaft,
The requirement is established in 29.1517:
Sec. 29.1517
Limiting height-speed envelope.
[For Category A rotorcraft, if a range of heights exists at any speed, including zero, within which it is not possible to make a safe landing following power failure, the range of heights and its variation with forward speed must be established, together with any other pertinent information, such as the kind of landing surface.]
Amdt. 29-21, Eff. 3/2/83
The overall position is discussed in the following paragraph from a 'response' document sent to EASA:
The issue is complex but if you have the stomach for an interpretation of the issue, it can be found in the 'response' document here:
The requirement is established in 29.1517:
Sec. 29.1517
Limiting height-speed envelope.
[For Category A rotorcraft, if a range of heights exists at any speed, including zero, within which it is not possible to make a safe landing following power failure, the range of heights and its variation with forward speed must be established, together with any other pertinent information, such as the kind of landing surface.]
Amdt. 29-21, Eff. 3/2/83
The overall position is discussed in the following paragraph from a 'response' document sent to EASA:
All Category A and B procedures (provided in accordance with Subpart B ‘Flight’ of Part 29) ensure that the helicopter can tolerate an engine failure on take-off or landing: for Category A, by providing profiles that have demonstrated engine-failure accountability; and, for Category B, by providing profiles that remain clear of the H-V avoid curve.
All dual qualified helicopters have a ‘capability’ (as expressed in the EASA definition of Category A) of using the Category A or Category B procedures; helicopters cannot be ‘operated’ in Category A or Category B they have to be ‘operated’ in accordance with the Performance Classes (or with exposure) – i.e. it is the ‘Code of Performance’ that determines which Performance Class has to be employed. Certification in Category A does not, by itself, mandate the use of the Category A procedures.
All dual qualified helicopters have a ‘capability’ (as expressed in the EASA definition of Category A) of using the Category A or Category B procedures; helicopters cannot be ‘operated’ in Category A or Category B they have to be ‘operated’ in accordance with the Performance Classes (or with exposure) – i.e. it is the ‘Code of Performance’ that determines which Performance Class has to be employed. Certification in Category A does not, by itself, mandate the use of the Category A procedures.
JimL.....the comedian....whoever would have guessed!
The issue is complex but if you have the stomach for an interpretation of the issue, it can be found in the 'response' document here:
