Go Back  PPRuNe Forums > Aircrew Forums > Rotorheads
Reload this Page >

Performance class two enhanced (offshore)

Rotorheads A haven for helicopter professionals to discuss the things that affect them

Performance class two enhanced (offshore)

Old 14th Feb 2010, 18:42
  #1 (permalink)  
manfromuncle
Guest
 
Posts: n/a
Performance class two enhanced (offshore)

I understand the rules are changing regarding this? For European offshore operations

I understand this will have a major impact in the Southern North Sea.

Can anyone point me in the direction of the details?
 
Old 15th Feb 2010, 17:35
  #2 (permalink)  
Deutz
Guest
 
Posts: n/a
PC2(e)

I’m not sure that you mean performance class two‘enhanced’. PC2(e) was a term which meant PC2 with exposure period during which a safe forced landing is not possible.

There is a good explanation of the concept in a closed JAA NPA. Try googling ‘JAA NPA OPS 38’. This has been lifted by EASA and is included in EASA NPA 2009-2B, for which a comment response document following the first round of consultation is awaited.
 
Old 15th Feb 2010, 17:47
  #3 (permalink)  
 
Join Date: Oct 1999
Location: Nigeria
Age: 54
Posts: 4,807
Deutz,
PC2e most certainly does not mean "with exposure period", in fact quite the opposite! The NPA you refer to was incorporated in JAR OPS-3 Amdt 5, and if you re-read it you will see that in essence what PC2e tries to achieve is a quasi - PC1, whilst recognising that a full PC1 guarantee is not possible in the offshore environment.

I'm sure JimL can give you chapter and verse on the subject, should he feel fit.
212man is offline  
Old 15th Feb 2010, 18:22
  #4 (permalink)  
 
Join Date: Aug 2004
Location: Aberdeen
Age: 64
Posts: 2,043
Just to be awkward, I would say that PC2E is performance class 2 with exposure time, where that exposure time is nominally zero. Which as 212man points out, is certainly not PC1.

The question is, is the probability of having an engine failure and ditching during the typical 4 seconds or so of exposure time when flying PC2, greater or less than the probability of having some other problem resulting from having to operate with minimum fuel to satisfy PC2E, such as:

Getting short of fuel because the TAF for your Coastal Airfield was way out (its fogged in) and you don't have enough fuel for an alternate, so you have no choice but to fly the approach anyway even though the RVR is 100m. Or something similar!

And what about the effect on overall safety by having to fly more sectors, because the payload for each sector is less due to PC2E constraints?

And what about some of the PC2E profiles the manufacturers have come up with - eg you must keep 40kts IAS on til the last moment, then big nose up attitude to stop in time, hopefully not hitting the structure in the process when you can't really see where you are going due to the nose up.

When did the last accident occur from an engine failure just on takeoff or landing? By contrast, how many aircraft have hit the structure due to misjudgment, or become dangerously short of fuel?

These are the sorts of reasons why some of the operators, and UK CAA, are rather against PC2E. Yes, when the other option was PC1 (impossible offshore) it was a good idea. Now EU Ops is all up for grabs, we think that the status quo is best - ie PC2 with controlled exposure time and the equipment (UMS etc) to retain confidence in engine reliability.

HC

Last edited by HeliComparator; 15th Feb 2010 at 18:51. Reason: typo
HeliComparator is offline  
Old 15th Feb 2010, 18:40
  #5 (permalink)  
 
Join Date: Oct 1999
Location: Nigeria
Age: 54
Posts: 4,807
JimL can give you chapter and verse on the subject, should he feel fit.
.....and HC will read you the other chapters and verses!
212man is offline  
Old 16th Feb 2010, 08:42
  #6 (permalink)  
 
Join Date: May 2003
Location: Europe
Posts: 870
Manfromuncle,

The rules were changed at AL5.

The effect on the SNS will depend on the equipment used; for the AW139 there will be no effect at all.

The effect on all NS operations will depend upon the operator's application of the rules. Take-off and landing in Subpart H (PC2) was always divided between: (a) the original ICAO principle of a safe-forced-landing (Pure PC); and (b) the use of Exposure. This did not change with AL5.

Examination of the revised JAR-OPS 3 will show that (both for take-off and landing):
Clause (a)(1) of the rule requires the base-line performance (second segment climb);

Clause (a)(2) is for operations other than with Exposure (with a SFL - i.e. Pure PC2); and

Clause (a)(3) is for operation with Exposure
The operator has the opportunity for application of either Pure PC2 or Enhanced PC2 (PC2e).

PC2e comes within (a)(3) because it is well known that (described in the guidance - as it was in the explanatory material for the NPA) environmental conditions of helideck operations do not always permit a deterministic outcome as prescribed in the Category A procedure. This is one of the reasons why operations cannot be in PC1 (another is the required size of the helideck surface (the TLOF)).

Application of Pure PC2 requires a safe-forced-landing - in the case of helideck operations that implies: (a) no deck-edge strike; and (b) a landing without injury to persons in the helicopter (a safe ditching). It has long been recognised that such a safe landing can be conducted in Sea State 4 and below (from AC 29-2C, significant wave height of 4ft - 8ft and wind between 17kts and 21kts).

Provided that a safe-forced-landing can be achieved, Pure PC2 can be conducted.

Helidecks have to be designed to provide a 180 obstacle free sector - oriented into the prevailing wind. Leaving aside the case of a sea that is running high with a slack wind (which is an issue that does has to be addressed) it follows that with a reported wind of 21kts or less, a departure or arrival will always be possible within the 180 obstacle free sector regardless of wind direction. If, for take-off, that is combined with a profile that assures deck-edge clearance, the conditions for Pure PC2 are satisfied. As wind accountability is never built in to the manufacturers procedures other than for drop down, a cross wind has no effect on deck-edge clearance.

Compare that with the pre-AL5 conditions and you can see that (for winds of 21kts or below) the only additional requirement is the provision of a profile that provides deck-edge clearance. (This does not take cognisance of the provisions that have already been made for low wind operations discussed in the other thread.)

The use of Pure PC2 is tied to a wind speed of 21kts or less (with the rider about significant wave height); this break is hard - i.e. not factored. If that wind is exceeded, then a safe-forced-landing is not assured and the operator has to apply the conditions of the provisions of (a)(3). If the break is hard, it can logically be argued that progression into PC2e should permit full credit for the first 21kts of the wind. Whilst this could not be permitted for a Category A procedure, it can for PC2e because of the flexibility of the provision:
"take-off mass takes into account: the procedure; deck-edge miss; and drop down appropriate to the height of the helideck..."
The situation with institutionalised ditching (albeit tied to a limit of SS4) provides an ethical dilemma for the oil companies; the acceptance of this situation is for them to deal with because it is one of duty of care. Before extensively flaming me for accepting this situation, please examine the status quo - operations with Exposure which encompass both the probability of a deck-edge strike and ditching in an undefined sea state.

In order not to provide a dense post, I will pause at this stage and let you consider what has been said.

I will resume later with: the provision of performance data based upon manufacturers graphs; the situation when the wind is in excess of 21kts and in the 150 limited obstacle sector; addressing the lack of (explicit) data for the HAPS landing manoeuvre by utilising manufacturer's statements and graphs; and examination of the 'proportion' of operations that may have to be conducted with an exposure element.

Hopefully, by the time the entirety of this has been discussed, you will see that most of HCs apocalyptic predictions are not based upon fact.

Jim

Last edited by JimL; 18th Feb 2010 at 19:14. Reason: Improved grammar
JimL is offline  
Old 16th Feb 2010, 14:33
  #7 (permalink)  
 
Join Date: May 2003
Location: Europe
Posts: 870
Firstly to the take-off masses:

Some mass figures which relate to the observations in the post above (addressing Pure PC2 and PC2e).

Using the manufacturer's data for, the AW139, the EC225 (included for HC's benefit), the EC155 and the S76C++.

Taking ISA SL conditions the following masses are provided by the graphs:

For the AW139:
PC2e - there is no drop-down with a mass of 6,400kg in nil wind up to ISA + 20
For the EC225:
The Pure PC2 mass is 10,875kg

The PC2e mass with an unfactored wind of 20kts is:
10,500kg for a 50ft drop down; and

11,000kg for a 100ft drop down (limited by the deck-edge mass of 10,875kg)

Zero drop down is achieved with an unfactored wind of about 35kts (extrapolated)
For the EC155:
The Pure PC2 mass is 4,750kg

The PC2e mass with an unfactored wind of 20kts is:
4,920kg for a 30 ft drop down (limited to 4,750kg)

Zero drop down is achieved with an unfactored wind of 27kts
For the S-92:
The Pure PC2 mass is 26,250lbs

The PC2e mass with an unfactored wind of 20kts is:
26,500lbs for a 50ft drop down
Zero drop down is achieved with an unfactored wind of 30kts
For the S=76C++:
The Pure PC2 mass is 11,500lbs (wind up to 10kts)

The PC2e mass with an unfactored wind of 20kts is:
11,700lbs with a drop down of 15ft

Zero drop down is achieved at 11,700lbs with 23kts of wind (extrapolated)
NB 'Zero drop down' is no drop down below deck level.

Jim

Last edited by JimL; 27th Feb 2010 at 15:23. Reason: Edited to add the S92 to the figures
JimL is offline  
Old 17th Feb 2010, 11:38
  #8 (permalink)  
 
Join Date: May 2003
Location: Europe
Posts: 870
To continue to the landing manoeuvre.

HC is absolutely correct when he points to the inappropriateness of some of the Helideck CAT A landing procedures. We can speculate that this was as a result of a decision to replicate the onshore helipad procedures. The onshore procedure provides a straight in continuous approach through the LDP to the landing point. (Previous versions of the guidance material also had a clause to include a landing after a failure at any point on the approach path - in later versions this is removed.) The LDP is the last point from which a balked landing can be carried out.

When providing procedures for a ground level helipad, a straight in approach with an LDP of about 40kts is reasonable because the (peripheral) cueing environment is sufficient to allow the positioning of the helicopter to the correct touchdown spot and it maximises the landing mass. For straight in offshore approaches there may be few peripheral cues and even those in front of the helicopter disappear from view when in a decelerative manoeuvre close to the helideck (one of the reasons for tail-rotor strikes).

It was for this reason that the HAPS landing profile was defined; with the HAPS profile, the Committal Point (CP) represents the last point from where a OEI SFL/balked landing can be carried out and the first point where a OEI sidestep landing can be safely performed (meeting the requirement for a SFL). It is recommended that the Dynamic CP is set to a point where: the helicopter blades are clear of the deck; the handling pilot has the deck at 2 or 10-O-clock; and with a closing speed of 10kts. If there are obstructions, the Offset CP can be used; this is at the side of the deck (not necessarily in the hover).

Manufacturers have been extremely reluctant to provide profiles using an LDP as defined for the Dynamic CP. We can only speculate that this is because the landing masses for a balked landing with nil wind will result in a large drop down. This HAPS manoeuvre with a CP was modelled some years ago and established that an engine failure one second before the CP resulted in a drop down slightly less than that experienced for the HAPS take-off manoeuvre in similar winds. (This is intuitive for those who have flown extensively on the North Sea using the HAPS landing profiles.) Using the Dynamic CP also reduces the drop down because there is always a residual speed of 10kts.

Up to recently it has been difficult to establish the drop down in the absence of appropriate landing profiles. However, in a recent manufacturer's publication, it was stated that drop down can be established from the take-off graph by using the actual mass and speed of the helicopter as an equivalent of unfactored wind.

As provided in the regulations quoted before, actions following an engine failure at or before the CP can be either: continue OEI and perform a SFL on the surface; or perform a OEI balked landing. Actions at or after the CP are to continue and perform a SFL on the helideck. Applying the regulations to the landing mass and using the methodology provided above and manufacturer's data, we have the following.

Taking ISA SL conditions (and the residual 10kts A/S) and applying a hard limit of 20kts unfactored.

The following masses are provided by the graphs for a Dynamic CP (for an Offset CP, the landing mass would be the same as the take-off mass):

For the AW139:
PC2e - there is no drop-down with a mass of 6,400kg in nil wind up to ISA + 20
For the EC225:
The Pure PC2 mass is 10,875kg (from the WAT graph)

The PC2e mass with an unfactored wind of 20kts is:
11,000kg for a 50ft drop down (limited to 10,875kg)
Zero drop down is achieved with an unfactored wind of about 25kts (extrapolated)
For the EC155:
The Pure PC2 mass is 4,750kg

PC2e zero drop down is achieved with an unfactored wind of 17kts
For the S-92:
The Pure PC2 mass is 26,500lbs

The PC2e mass with an unfactored wind of 20kts is:
26,500lbs for zero drop down
Zero drop down is achieved with an unfactored wind of 20kts
For the S=76C++:
The Pure PC2 mass is 11,500lbs (wind up to 10kts)

PC2e zero drop down is achieved at 11,700lbs with 13kts of wind (extrapolated)
NB 'Zero drop down' is no drop down below deck level.

The implication of the zero drop down is that the arrival sector widens to the 210 degrees of the limited obstacle sector (where all obstacles have to be below the level of the deck).

Last edited by JimL; 27th Feb 2010 at 15:21. Reason: Edited to add the S92 to the figures
JimL is offline  
Old 17th Feb 2010, 22:54
  #9 (permalink)  
 
Join Date: Aug 2004
Location: Aberdeen
Age: 64
Posts: 2,043
Blimey JimL, you are on a roll!

Just picking up on your "apocalyptic" comment at the end of your first post, neither the introduction of PC2e, nor the non-introduction of PC2e would be apocalyptic. However I suggest that there is little point in changing established procedure and introducing additional complexity unless a clear safety benefit can be identified.

Both the probability of an engine failure on takeoff or landing causing a crash/ditch without PC2e, and the probability of one of my "apocalyptic scenarios" occuring with PC2e, are very slight. However it has to be said that the former has never occured in the history of the N Sea, whereas the latter has occurred from time to time, in at least 1 case with fatal consequences.

So which ever path is finally taken, there will be little effect on overall safety. My point is why make a change for change's sake when the previous sentence is true? And without any proper analysis so far, it might well turn out that in fact the introduction of PC2e reduces overall safety.

But this argument is probably unanswerable with current information.

So how about:

If PC2e relies on accurate offshore wind data for performance calculations, will all offshore installations have to have approved wind measurement equipment/locations? (currently they are not approved as far as I am aware).

If I am shuttling and have arranged my fuel / arrival and departure weights to be within PC2e limits for the current offshore reported wind and client load, but whilst I am on deck for the normal 15 mins or so, the wind drops a bit so now I am over weight, what should I do? Bump passengers?

If I have that (admittedly never yet experienced) engine failure on rotation and clip the tail on the deck edge, spin into the water and kill someone, and its discovered in the investigation that I rotated 0.5 seconds (4ft) too early compared to the profile used to calculate deck edge clearance, will I go to prison?

HC
HeliComparator is offline  
Old 18th Feb 2010, 08:46
  #10 (permalink)  
 
Join Date: May 2003
Location: Europe
Posts: 870
Hi HC,

As you know from our previous discussions, there is nothing new in my posts I am merely using data that is currently available, and restating other facts.

All aircraft use the existing wind measuring equipment to apply the limitations contained in the HLL. Will that change? Probably not. Even at this time JAR-OPS, permits the operator to take advantage of an improved wind factor - surely that is an incentive to improve this equipment. In order to strengthen your argument, you have a tendency to make assumptions that were not part of any proposal. Why was it do you think that the authors went to such trouble to emphasize the difficult nature of the offshore environment? Your whole argument depends upon something that you state you wish to avoid - confusion between PC1 (and the Category A procedure) and PC2e.

As you will have seen from the mass caculations, your previous statement about the knock-on effect on passenger loads was something of an exaggeration. With regard to a change of wind, such conditions already apply; what would you do now if you were operating an EC155 and the wind dropped from 10kts+ to 5kts? Would you apply the 300kg reduction in payload?

You should already know the answer to your final question because it is specifically mentioned in the ACJ; after discussion of a number of issues which affect the profile, it states:
"Under these circumstances, the Commander might adjust the profile to address a hazard more serious, or more likely, than that presented by an engine failure"
A number of your scenarios link the application of PC2 with other issues - one of which was fuel calculations. The calculation of fuel is completely independent of performance, it should be based upon safety, the company SOPs, and be compliant with the requirements - one of which is the ability of the Commander to add fuel for contingencies. This calculation comes before any load is offered to the customer. In any case, the masses shown above should not create a seismic shift in fuel policy (unless it is not currently based upon calculation but on a fill-it-up mentality).

Perhaps I sense a change in tone; we are now discussing the implementation of the rule and not non-compliance.

I find your statement:
Now EU Ops is all up for grabs
somewhat frivolous and naive. No changes were proposed (in performance) from JAR-OPS; I am also reliably informed that there were no objections to the AL5 changes in the comments to the NPA for offshore operations.

Perhaps the oil companies need to examine the facts with regard to compliance and performance and not be swayed by emotive arguments that cannot be substantiated. What price ALARP - are we confusing practical with convenient?

More later but consider this; if Pure PC2 (as described in my previous post) is employed, it will remove the probability of deck-edge strike from about 70% of offshore movements (take-off and landings). With a wind in the 180 sector, PC2e will remove the probability of a deck-edge strike and ditching in high sea states. How do they rate as safety benefits?

Stop just thinking EC225 and consider all helicopters.

Jim

Last edited by JimL; 18th Feb 2010 at 09:22.
JimL is offline  
Old 18th Feb 2010, 17:55
  #11 (permalink)  
 
Join Date: May 2003
Location: Europe
Posts: 870
Here is an attempt to quantify the benefit of the extant regulation with respect to the reduction in Exposure; in order to do this it is necessary to establish those operations which are potentially:
without exposure; and

where exposure might remain.
Firstly we need a reasonable basis for assessment. During the modelling of PC2e, access was provided to an operator’s database of weather reports (INTOPS).

INTOPS provided us with 39,131 North Sea wind data points (reports) for a four year period. Using this data we established that:
Wind <= 20kts occurred in 22,725 reports or 58%

Wind >20kts but <30kts occurred in 8,577 or 22%

Wind >30kts occurred in 7,829 reports or 20%
The following assessment assumes a helideck which is compliant with Annex 14 Volume II – as implemented in Cap 437. The orientation is not assessed but it is assumed that, if the CAP 437 recommendations have been followed, the Obstacle Free Sector is oriented into the prevailing wind; if this is the case, the figures shown below will be pessimistic.

Using the figures shown above, we are able to estimate the likely proportions of: non-exposed; potentially non-exposed; and potentially exposed, operations.

Non-Exposed

Wind at or below 20kts in all sectors:
Pure PC2 can be flown in 58% of all take-off or landing cases
Wind in excess of 20kts occurring in the 180° sector:
PC2e can be flown in 21% of all take-off or landing cases
This accounts for 79% of take-off and landings.

However, each aircraft has a zero drop down mass that is associated with an unfactored wind - if we assume that this wind is 30kts (not an unreasonable assumption given the figures provided in the calculated masses) then PC2e (without exposure) can be flown for an additional (30/360 x 20%) 1.7% of flights – i.e. when the wind is > 30kts and in the (30°) LOS (no obstacles above deck height).

This raises the non-exposed operations to 80.7%.

Potentially Non-Exposed

Wind >30kts and in the 150° obstacle sector
PC2e with zero drop down occurs for (150/360 x 20%) 8.3% of flights
In these cases, exposure is undefined but is tending to zero. As the wind increases all aircraft reach the point where OEI HOGE is achieved (just below the lowest Vtoss).

The exception to this occurs on those decks with turbulent sectors; this is, and should continue to be, dealt with in the HLL.

Potentially Exposed

Wind is >20 and <30 and in the 180° sector
We have 11% of flights where, potentially, there would be exposure.
In Summary

Operations without exposure are likely to be 80.7% of the total.

Operations where exposure tends to zero is likely to be 8.3% of the total.

Operations with exposure is likely to be 11% of the total.


Conclusions

Whilst there are operations in the North Sea where there is de facto no exposure, this has never been quantified (apart from operations with the AW139). Using the actual wind data and the examples of masses shown previously this can now be done.

We continue to base the take-off and landing masses on the clear area WAT just so we can establish the second segment climb – this is no longer satisfactory.

There were several reasons why there were change to the regulations, the most important of which was to provide a signal to manufacturers that future aircraft should be capable of providing exposure free operations.

To do nothing but justify what is already done will result in the continuation in operation of existing underpowered models and hold out the prospect of no change in the future.


Jim

Last edited by JimL; 29th Mar 2010 at 14:35. Reason: Correction of the calculations; the previous calculations put the 20kts wind in the >20 and <30 group. There a substantial differences with the 20kts wind in the correct group.
JimL is offline  
Old 18th Feb 2010, 18:55
  #12 (permalink)  
 
Join Date: Apr 2003
Location: 18 Degrees North
Posts: 699
my understanding is the implementation date has only slipped from 1st Jan to 1st July 2010 at the moment !
Camp Freddie is offline  
Old 18th Feb 2010, 20:45
  #13 (permalink)  
 
Join Date: Aug 2004
Location: Aberdeen
Age: 64
Posts: 2,043
JimL

Trying to leave the personal comments out of it, I still feel that you are not addressing the very point that you mentioned - risk ALARP.

By fixating on engine failures as the only source of hazard, I maintain that there is a danger that you replace one extremely remote hazard with others that, whilst also remote, are possibly less remote than the engine failure during the critical few seconds.

Without a balanced assement of all the risks, I don't see how you can claim that PC2e leads to overall risk ALARP. I agree that such an assessment is not particularly easy to quantify, but to omit it is to be blinkered.

Regarding the point about "the continuation in operation of existing underpowered models" and the nil wind thread, I think you are confusing AEO performance with OEI performance. The former is typically limited by transmission or rotor head and not by engine power. The latter is related to installed engine power.

Therefore there can be no guarantee that operation to PC2E will in any way help the AEO case of some of the newer underpowered aircraft such as the 155 - not too bad OEI due to its engines' 30 sec rating, but pretty poor AEO. Operating PC2e from a high deck would still allow high takeoff mass so not addressing the AEO performance issue.

Modern aircraft with marginal AEO performance can be more dangerous than their predecessors due to FADEC AEO power limiting. In an older aircraft one can in extremis normally pull to max contingency power on both engines. No doubt damaging the transmission but maybe not actually crashing.

Modern aircraft typically limit AEO power to the certified transmission limits, so you won't overstress the MGB but unfortunately you might crash as a result. Even those that have FADEC blowaway are little better because whilst the older aircraft can give max power on both engines whilst the rrpm is still normal, those with FADEC blowaway only give max power once the rrpm has become very low. Since thrust is a function of rrpm and torque, an overpitching crash is more likely in the new types, eg following an unexpected event such as weather or structure-induced downdraft.

So I am all for increasing AEO performance since this has potential benefit on every takeoff and landing, except the 1 in 10^9 when the engine fails during the few seconds of exposure. But its not related to OEI power nor to PC2e.

(sorry for thread drift on to AEO power, but you started it!)

HC

Last edited by HeliComparator; 18th Feb 2010 at 21:27.
HeliComparator is offline  
Old 18th Feb 2010, 21:20
  #14 (permalink)  
 
Join Date: Dec 2006
Location: UK and MALTA
Age: 58
Posts: 1,259
Hi Jim,

Thanks for the explanation, I am still digesting some of it. A quick question...how does the proposed mass calculations compare to the existing performance requirements for a HOGE AEO...providing the necessary thrust margin for take-off and landing. This seems to work well with the existing HAPS profiles.

DB
DOUBLE BOGEY is offline  
Old 19th Feb 2010, 08:11
  #15 (permalink)  
 
Join Date: May 2003
Location: Europe
Posts: 870
HC,

Deck-edge clearance is dependent upon an acceleration to the RP, this is always achieved AEO. If, as discussed in the other thread, the aircraft cannot achieve this acceleration, it certainly will not be able to meet the requirements of the profile. As is commonly understood, it is kinetic (acceleration and residual rotor energy) and potential energy (height at the RP) that provide clearance from the deck-edge, and OEI power that reduces the drop down.

Exposure does not just last for a few seconds (except for aircraft which can comply with little effort or impact on cost) nor can it ever be contained within 1 x 10**-9 (unless the engines could be made super reliable - in which case we wouldn't be having this debate). With existing aircraft the risk still contains both elements - deck-edge strike, and ditching without a SFL.

With regard to ALARP there are two sides to the equation; before it can be assesed we need to move the discussion back to the operational costs. I would be interested in a re-assessment (using the figures from the RFM provided earlier) of the impact of compliance upon loads and fuel. Is it still the contention that compliance will impact detrimentally upon fuel loads or result in (more than) a 30% increase in flights?

How much endurance does the EC225 have with a take-off mass of 10,875 and 19 passengers?

DB,

I have not compared the numbers so I am not sure; AEO HOGE was the first attempt to set a minimum standard but, as HC points out, it is the combination of AEO and OEI which provides protection throughout the profile. In fact the use of thrust margins to establish take-off masses is extremely difficult to achieve, as is the provision of a simple metric establish the PC2e mass. Notwithstanding that, I still cannot see how the flight conditions stated in the low wind thread would occur with AEO HOGE power (unless someone can explain).

Jim

Last edited by JimL; 19th Feb 2010 at 14:50.
JimL is offline  
Old 19th Feb 2010, 08:17
  #16 (permalink)  
 
Join Date: Oct 1999
Location: Nigeria
Age: 54
Posts: 4,807
DB,
the procedures normally require a delta torque figure to be used that ensures a minimum rate of climb at the rotation point. This is to ensure deck edge clearance (at least 15ft.) for low decks the RTOM is limited by the drop down available, but as the deck height increases you reach a 'cross-over' point where deck edge clearance becomes the critical parameter, and increasing the height has no further benefit (on RTOM.). So, by definition, there is no specific reference to OGE AEO performance as the graphs have already allowed for the appropriate delta torque being available.

Last edited by 212man; 19th Feb 2010 at 08:19. Reason: To correct fat fingered iPhone typos!
212man is offline  
Old 19th Feb 2010, 13:23
  #17 (permalink)  
 
Join Date: Jun 2003
Location: United Kingdom
Age: 57
Posts: 24
HAPS

Can someone remind me of what the acronym HAPS stands for. I cannot get access to TGL 14 from the JAA website as it requires a password for some reason. Thanks in advance.

JimL - I note that the CAT A elevated heliport profiles on some types require a TDP of 30ft. This is in the avoid curve in light or nil wind. How does that work legally for PC1 which the CAT A profile is designed for. ie onshore off a hospital roof?

Is it that the reduced mass effectively means you are not in the avoid curve - the avoid curve assumes max certified gross weight?
Lenticular is offline  
Old 19th Feb 2010, 14:47
  #18 (permalink)  
 
Join Date: May 2003
Location: Europe
Posts: 870
Lenticular,

All phases of a Category A profile have to be outside the HV Curve - in some manuals it does state that the HV Curve is modified by the procedure. A number of CAT A profiles do not result in a reduction of take-off/landing masses. As the profile becomes more vertically oriented, or shortened, there can be a penalty to pay.

HAPS means Helicopter Airfield Performance Simulation - a 2D modelling programme written by WHL. This was superseded later by the 3D RESPECT/EUROPA model (a collaborative project of European research establishments and manufacturers which built on the HAPS model).

Optimised helideck take-off and landing procedures were, under the auspices of the CAA, investigated and modelled by WHL when providing the HAPS profiles. Whilst this work did not lead to (a method for) the establishment of take-off and landing masses, the procedures did reduce the time that the helicopter was at risk. The HAPS procedures (without the provision of masses) have been successfully utilised for several decades.

Here is a description of the HAPS model:
"The Helicopter Airfield Performance Simulation (HAPS) program is a modular simulation program, designed to simplify the process of developing new techniques and modelling new aircraft. It has evolved directly from the simulation programs developed over many years to model the dynamic behaviour of a number of helicopters from the Wessex and Sea King to the Lynx and Westland 30.

The model takes the form of a longitudinal flight path simulation. The simulation considers only longitudinal symmetrical forces and motions with the exception of tail rotor thrust and power, which are also calculated because of their effect on the aircraft power required.

The model employs expressions derived from simple strip theory to calculate rotor thrust, collective pitch, rotor in plane force and fore and aft flapping. The induced velocity is calculated from momentum theory, and an empirical factor, based on forward speed and weight, is used to correct for non uniformities in the downwash field. The tail rotor power is calculated from the thrust required to balance the main rotor torque, and the lift, drag and pitching moments of the fuselage are derived from stored wind tunnel data.

An iterative process is used to establish the initial steady state (un-accelerated flight) condition. The dynamic section of the simulation model is then entered and time is incremented in discrete steps. At each time step, control movements and engine power are used to calculate the aircraft and rotor accelerations and a constant derivative integrating process is then used to calculate the aircraft's rate, position values and rotor speed prior to the next time step.

The control inputs may be applied in a number of ways:
Collective pitch defined in data arrays prior to running the program.

Collective pitch automatically evaluated (pilot simulation) to achieve pre defined rotor speed, engine power, rate of descent or normal acceleration patterns

Pitch attitude defined in data arrays prior to running the program required pitch acceleration is calculated, from which cyclic pitch is derived.

Cyclic pitch automatically evaluated (pilot simulation) to achieve pre defined pitch attitude or longitudinal acceleration patterns.
The engine power is calculated using a representation of the static droop law or isochronous rotor governor and is, therefore, primarily dependent upon rotor speed and collective lever position.

Engine failures may be scheduled at any point in the program run, after which the power of the failed engine follows an exponential decay whilst the live engine is allowed (if the engine governor demands it) to increase to a pre determined maximum (typically the brochure maximum contingency level). At less than nominal rotor speeds this maximum power level is reduced to simulate the reduction in turbine efficiency."
Jim

Last edited by JimL; 19th Feb 2010 at 15:00.
JimL is offline  
Old 20th Feb 2010, 08:16
  #19 (permalink)  
 
Join Date: Jun 2003
Location: United Kingdom
Age: 57
Posts: 24
JimL - Thanks for the information, its intersesting to get an insight to the development of what we do on a daily basis.

Your statement
All phases of a Category A profile have to be outside the H/V Curve
is interesting. As an example the Ground helipad CAT A profile for the EC155 has a TDP of 100ft and is a vertical climb to that point. However, the avoid curve starts at 5ft and extends to 300ft. At 100ft, 15kts of wind would put you on the front edge of the H/V curve so assuming nil wind you are well into the H/V avoid area. The only plus is you are mass restricted.

There is no statement in the RFM that modifies the H/V graph.
Lenticular is offline  
Old 20th Feb 2010, 09:33
  #20 (permalink)  
 
Join Date: Aug 2001
Location: Cornwall
Age: 72
Posts: 1,305
H/V Curve

Len

The dynamics of the situation - Cat A take-off -v- HV Curve - are completely different and it is quite possible that passage through the HV Curve is a necessary part of the Cat A profile.

The certification process for delineating the HV Curve is, I believe, one that is essentially static without the acceleration that characterises a take-off. All Cat A profiles are certified and therefore approved and to achieve that they will have been demonstrated with engine failures at all critical points.

If that profile seems to contradict the HV Curve then I am sure it is only a problem of perception, not a real one.

G.
Geoffersincornwall is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright © 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.