Helideck takeoff with S92A

[Ardbeg]

Wondering if You Ppruners could help me out with an operational question regarding "elevated helideck takeoff" with the S92A.
When AEO in the RFM it states "...rotate the aircraft 10 to 20 degrees nose down".

Question: From what attitude are those 10-20 degrees mesaured?
Is it the hover attitude (normally 6-8 degrees nose up), or is it the artificial horizon?

rgds
Ardbeg

[rotordude]

We had the same question a while back. Further investigation (I guess Sikorsky was contacted) revealed that it was relative to the horizon in both AEO and OEI scenario.

Rotordude

[onemorepilot]

Hi Ardbeg

In September 2006 this statement came from Sikorsky, that says that these 10-20 degrees should be from the "vertical climb attitude". Not the artificial horizon. Are Sikorsky changing minds?

In step 9 of the vertical take off procedure, when we say "10 to 20° nose down" we mean from the vertical climb attitude (which usually matches the hover attitude). If you are climbing/hovering at 5° nose up, then you will pitch over to 5 - 15° nose down on the attitude indicator.

For those who has access to the S92A RFM can see that a small word "to" before "20 degrees nose down" in OEI indicates a reference to the artificial horizon.

In AEO it states "10-20 degrees nose down" without that small but crusial word "to", which indicates that the statement from Sikorsky Sep.-06 is the correct interpretation.

Any opinions from other S92A operators?

rgds
OMP

[Senior Pilot]

Not Sikorsky, but Bell in the 412 FM require a nose down pitch of 10 degrees from the hover attitude, not the horizon. The ADI pitch bar is required to be adjusted to indicate level whilst in the hover, prior to Cat A departure, then 10 degrees is taken from that setting.

[JimL]

The helicopter should be rotated through 10 - 20 degrees (and this should have been the wording in the RFM). The 20 degree rotation should be applied in low winds and reduced incrementally to 10 minimum in higher winds; if 20 degrees is used in higher winds, the helicopter will descend below the level indicated in the drop-down graphs.

The actual figure (between 10 and 20) is left to the pilot because it would be difficult to require an exact pitch attitude adjustment.

As you will appreciate it has to be this way because the attitude of the helicopter varies with CofG.

As indicated by Senior Pilot, it used to be the practice to level the 'wings' in the hover (or place it to some other level); this is no longer the practice - adjustable horizons are somewhat out of favour.

Jim

[212man]

Yes - as stated above, it's a delta, not an absolute value.

The point is it is the disc that needs to be rotated , not the aircraft, and so to some extent the actual fuselage attitude is irrelevant.

During the landing flare, however, the values quoted are absolute, as the fuselage attitude is a factor close to the ground.

[Ardbeg]

So the conclution is......

S92A RFM should be interped that during AEO pitch attitude change of 10-20 degrees is from hover attitude, not artificial horizon.

The aircraft rotates through 10-20 degrees, (a delta value).

Depending of variable factors as wind, weight, temp, CoG it is up to the pilot to choose how much rotation is needed. Minimum 10 degrees below hover attitude, up to maximum 20 degrees below hover attitude.

By doing so the pilot creates ,after rotation point, a take off profile that never goes under the height of the helideck, and reaches Vtoss quickest possible.

How come then the investigation that Sikorsky (maybe) was involved with state that the reference is the artificial horizon?
20 degrees below the artificial horizon one intense rotation for being normal takeoff.

ardbeg

[rotordude]

Sorry Ardbeg!
I was a bit trigger happy on my first reply. Looks like I misinterpreted the information from Sikorsky when I read it. The other replies makes perfect sense.

No wonder then why all the passengers are screaming their heads off when I do the helideck takeoffs :}.

[Shawn Coyle]

All of which points to a requirement for the FM to be more clear...

[JimL]

Ardberg,

Not quiteBy doing so the pilot creates ,after rotation point, a take off profile that never goes under the height of the helideck, and reaches Vtoss quickest possible.Firstly, the manoeuvre must ensure deck-edge clearance - a target 15ft - and this is part of the 'take-off mass' calculation

Secondly, the helicopter may descend below the level of the deck and the 'take-off mass' is adjusted so as to minimise this drop-down (the helicopter remains above - a target of 35ft - the highest obstacle in the take-off path).

Thirdly, the manoeuvre is balanced to minimise both the min-dip and the distance to min-dip (where min-dip is the lowest point reached in the take-off path).

Finally, this is a PC2e calculation/manoeuvre and not Category A/PC1.

Jim

[Vertolot]

JimL,

So, if I understood right. When you do a take-off from a helideck you first climb vertically to CDP (maybe 20 feet) and then you rotate 10-20 degrees nose down. You have made calculations for your drop-down that you will get a 35 feet clearance from the highest obstacle in your take-off path and this will be a PC2e operation. Are PC1 operations used off-shore for helideck departures or landings??

Thanks,

[Geoffersincornwall]

JimL will be back shortly I'm sure and he can fill in the gaps but basically NPA 38 to JAROPS 3 was tabled to deal in part with the dilemma caused by the realisation that the obstacle environment offshore (moveable obstructions that create variable degrees of turbulence and heat pollution and thus thwart all attempts to make the operation 'predicatable' in performance terms).

It is not therefore possible to use PC1 offshore - PC2 (enhanced) is as good as it's going to get - for the time being.

G.

:ok:

[bpaggi]

t is not therefore possible to use PC1 offshore - PC2 (enhanced) is as good as it's going to get - for the time being.


I personally disagree with this statement. Surely PC1 can not be always available in offshore operations but it can be used provided the environment will meet the OEM RFM performance.
This off course will also depend upon A/C performance, this makes the difference.

[JohnDixson]

OMP, do you recall the Sikorsky source for the document calling for an attitude change from trim of 10 to 20 degrees? I'm missing something about that and would like to follow it up.

Thanks,
John Dixson

[Geoffersincornwall]

BPAGGI

The difficulty faced by the offshore helicopter pilot is that he cannot predict the turbulence levels that he will encounter neither can he predict the degree of heat and turbulence generated by turbine exhausts located in the helideck area. The unfavourable effects of turbulence are NOT catered for in the RFM. Neither is a sudden 5 degree increase in ambient when you slide over the helideck although if this characteristic is known and understood the WAT should be computed using the higher temp.

When we started this offshore game over 30 years ago you basically tossed the RFM overboard when you crossed the coast outbound and reverted to military thinking for the rest of the trip. We did Cat A (equivalent to PC1) on the beach but busked it when we got to the rig or platform.

The early recognition that this situation could not continue led to an attempt to quantify vertical performance by using HIGE data (assuming it was available in the RFM). This proved to be inadequate so the weight expectations were reduced by using HOGE as the target weight. Even this proved to be too much and in some companies this is then factored by 2.5% by day and 5% by night. In the North Sea companies have signed up to the use of a system whereby each helideck environment is analysed and a type-specific decrement to the planned landing weight is applied by all. (this to avoid the situation where one company's pilots claim to be 'more skillfull' and take a job turned down by another).

We cannot easily put Cat A profiles to good use offshore either. For example the TDP for the AW139 Cat A Vertical Helipad is too high. The loss of visual contact with the helideck will occur at about 15-20 feet and the consequences of a missed re-land after engine failure are too severe in this offshore environment. A 35 feet TDP on the 139 may well be the result of a focus on not descending below the helipad height following an engine failure after TDP.

If a mandate to operate PC1 is provided by a regulator then the following three elements MUST exist to be compliant:

1. The helicopter must be at or below the weight for PC1 (Cat A) WAT
2. The correct profile must be accurately flown as per RFM.
3. The obstacle environment must be in line with the requirements expressed in the RFM (TODR/RTODR).

The point is that performance is then PREDICTABLE and can be computed PRIOR TO DEPARTURE. There have been many situations when, knowing about the decrement situation, the platform sends a weather report that to put it mildly, is optimistic. Crews are then faced with a dilemma but wise heads will either turn around or land on a nearby 'unrestricted' platform and decant some pax before shuttling them across. The commercial pressure in this situation is enormous and for the many who have 'given-it-a-go' (me included) it can be an embarassing way to learn about life.

Of course if you are over the Cat A WAT and the site you are working from has not been subjected to detailed survey then you can still use the Cat A profile - but don't kid yourself that this makes it Cat A. Still, if the Cat A profiles were the ones you practiced in the sim (and I hope you do go to the sim) then at least you know how to react if the donkey stops. Also remember all the deck perimeter obstructions that can impinge on your landing and take-off. We have had 3 or 4 incidents this year where helicopters have struck obstacles close to the helideck.

So to respond to BPAGGI's assertion that PC1 can still be used offshore the answer is 'yes - you can use the profile and even be at the correct WAT for a turbulence-free environment, but that doesn't make it PC1 compliant'.

G

[onemorepilot]

Mr Dixson

Here's the info I'm refering to. Came informally 6:th Sep. 2006 to by then our Chiefpilot after quesions raised by linepilots how to interped the text regarding helideck take off.

In step 9 of the vertical take off procedure, when we say "10 to 20° nose down" we mean from the vertical climb attitude (which usually matches the hover attitude). If you are climbing/hovering at 5° nose up, then you will pitch over to 5 - 15° nose down on the attitude indicator.



In step 10 of the vertical take off procedure, when we say "rotate to an attitude of approximately 5° nose up" we mean 5° nose up on the attitude indicator.



Please note that in both of these cases we give you either a range of attitudes or use the word "approximate". The initial nose down attitude in step 9 is intended to get you to Vtoss as soon as comfortably possible. I personally would go closer to 10 - 15° down during the day with good visibility. I might only go to 5° nose down at night or during other times of low visibility. You also have to take passenger comfort into consideration. The 5° nose up in step 10 is just an initial target to get you to Vtoss. The actual climb attitude will be whatever it takes to maintain the correct airspeed. In the off shore oil rig case, since you will have cleared all obstacles immediately after takeoff, you can accelerate directly to 80 kias.

OMP

[JimL]

Vertolot,

As Geoff has saidIt is not therefore possible to use PC1 offshore - PC2 (enhanced) is as good as it's going to get - for the time being.This needs to be explained:

Firstly Bpaggi is correct that, with the appropriate helicopter, PC1 can be available for a proportion of the time; for the AW139, that will be a larger proportion than for some other less powerful types. It is for that reason, PC1 cannot be mandated.

If your RFM contains a Category A Helideck (S76C+) or a PC2 Helideck (S92A and B412) procedure that is the one you should use. You should be aware of limitations of a Cat A Helideck procedure which could prevent its use (which could be the requirement for additional equipment or specific deck markings).

One of the Cat A limitations might be the size of the take-off surface; look at the RFM for your helicopter and check the minimum size, in most cases it will be more than the 1D provided as a Standard for helidecks offshore. This limitation is more to do with the ability to retain a visual reference within the FOV (this will be more severe on toadstool type well-head platforms – this might be mitigated with better procedures using oblique departures).

PC2e remains silent on the size of the helideck.

Another might be the crosswind limitations of the procedure; all of you who fly offshore will be familiar with the requirement for a 180° obstacle free segment (based upon the 5 in 1 falling gradient). If the wind is strong and outside that segment, a take-off using the Cat A procedure might not be possible within the limits of the procedure. In addition, a Category A procedure is deterministic and depends for obstacle clearance on a reasonably accurate assessment of the wind; if the wind is from the obstacle segment it is likely to be turbulent (and contain vertical components); establishing a pure wind vector will be problematic.

PC2e relies upon normal cross wind limitations and uses notional obstacle clearance (deck-edge clearance and drop-down appropriate to the height of the helideck); it is implicitly understood that take-off into the Limited Obstacle Segment (a 210° segment in which the 180° segment is contained) can be performed because it should only occur when cross wind limitations would be exceeded, at which time the helicopter will be approaching minimum drop-down regimes. Most offshore pilots will know that the most extreme of these manoeuvres is when the pilot (in a strong wind) is facing directly into the obstacle segment, when a sideways rotation is taken from the RP.

Lastly, the Cat A procedure assumes: a stable helideck; a continuous approach profile from the LDP; and a reject following a failure before TDP. Operations to a moving deck tend to fall outside those parameters (see the discussion in ACJ to Subpart H paragraph 7.4.2).

Now to answer Vertolot’s question:

The procedure needs to provide: a vertical acceleration segment (providing inertial energy); kinetic energy in the Rotor speed (permitting droop); and potential energy in the height of rotation (the RP). It must avoid a manoeuvre which results in a move backwards into obstacles or puts the pilot in a position where visual reference cannot be maintained following an engine failure before RP (which might also be a factor in a too aggressive vertical segment – for example when the helicopter is light). This limits the maximum height of the RP (or results in a torque delta).

The procedure and RP chosen by the manufacturer will provide an optimised combination of all of the above. These manoeuvres are complex and are associated with the calculation of take-off masses to achieve deck-edge clearance and minimising drop-down whilst staying within the limitation of the helicopter. The manufacturer could provide two graphs: the first will provide the maximum mass for which deck-edge clearance will be achieved; the second will modify that mass to reduce drop down. The pilot should use a modified mass that ensures compliance with the appropriate rules.

In providing the take-off mass, the graphs might also ensure that the second segment climb performance (150ft/min at Vy and 1000ft) and AEO HOGE are provided (B412). The pilot is still responsible for ensuring that en-route performance is achieved.

With respect to larger decks: manufacturers are also considering providing distance to descent below the helideck level (could also be seen as the absolute deck-edge clearance). This would ensure that a take-off can be taken from the TPM (bum line) on a deck which is larger than 1D without compromising the clearance.

Jim

[JimL]

Onemorepilot:

The pitch attitude figure is performance related and not comfort or visibility related. If on a windless day you loose an engine one second before RP (pilot recognition and intervention time) and only rotate through 10 degrees, your deck-edge miss is unlikely to be achieved.

On the other hand, you have the same failure on a 30kt plus day and rotate through 20 degrees, you are likely to exceeed your predicted drop down.

However, the probability of a failure at that point on any day is about 1x10**-9 so no sleep should be lost worrying about it.

Jim

[Vertolot]

Hmmm, very interesting! Thanks for the replies.

[onemorepilot]

The text that is Italic in my former reply is all from Sikorsky. Including the last part mentioning comfort to passangers. Not any extra information from me personally.

Unfortuantly (yes embarassing) I`m struggeling to find out the source within Sikorsky where it came from. The former Chiefpilot who has that information has left the company.

OMP

[212man]

I will be at the S-92 Filght Ops Group next month, so will bring this topic up, as it will flow naturally from other related topics.

Jim,
could you explain your reasoning that drop down will increase with wind speed? Given that up to 120 ft drop down, the S-92 is deck edge clearance limited in nil wind, I fail to see how for a given RTOM and ambient conditions, a constant nose down pitch attitude will result in greater drop down with increasing wind speed. What the wind speed will do is allow a greater Vtoss to be attained in the same drop down and therefore a greater MTOM, though as Vtoss tends to Vy this advantage will clearly disappear.

In an etreme case where the Vtoss is equal to the wind speed, then I can see that the application of nose down pitch will be unecessary, and will result in height loss that was not required, but I can't see this being greater than the height loss needed to achieve this airspeed in nil wind conditions.

Luckily, as we have no wind, I don't have to worry too much about this......:E

[JimL]

Hi 212man,

In fact you capture the phenomena in your penultimate sentence.

It is not absolute drop-down but relative drop-down that is the issue; what we found with a given wind speed - say 30 kts (which was the wind in the iteration cycle that we found the effect and modelled extensively) - a pitch attitude application of 20 degrees showed a drop down below the deck (it was about 50ft as I remember it); with a pitch angle of 10 degrees there was no drop down below the deck (although it did drop down to deck level from an RP of 25ft). There was no real effect on deck-edge clearance.

With a nil wind, a pitch attitude of 20 degrees was required to clear the deck; no secondary effect was modelled because deck-edge clearance (of 15ft) was the primary target.

You concentration at the meeting needs to be with the landing procedure (as previously briefed) - that is much more problematical.

Jim

[Ardbeg]

Looks like JimL has very high knowledge regarding procedures. Appreciate very much that you share that knowledge.

Just a small thing, I see you yesterday replyed to OMP, OEI during helideck takeoff in a way like that was the original question.
The original question was regarding AEO that is possible to misunderstand when reading the RFM.

In the RFM it states very clearly in case of OEI after TDP you schould rotate the aircraft to 20 degrees nose down. In other words 20 degrees below artificial horizon.

But in the RFM it states not so clearly how to rotate (10-20 degrees) during helideck takeoff AEO (from hover attitude/artificial horizon). But thanks to excellent inputs from you Ppruners I now grasp the concept.

ardbeg

[onemorepilot]

Has the meeting been held yet? If so, what was said regarding the subject "from trim or not from trim"?

OMP

[212man]

I have it on very good authority, that the intent in the wording in the RFM is that for AEO operations the figures quoted (10-20 degrees) are a delta, and that for the OEI case (20 degrees) an absolute value.

E.g you are hovering with 5 degrees nose up, on rotation you rotate to 5-15 degrees nose down on the ADI - the actual value dependant on factors such as pax comfort and day/night operations. If the engine fails, you rotate to 20 degrees nose down on the ADI.

20 degrees is a compromise between maximum acceleration to Vtoss and excessive rate of descent.

It is accepted that there may be some ambiguity in the current description and it will be addressed at a future RFM re-write. Hope that clears that up :ok:

[onemorepilot]

Thanks

A statement that corresponds to the RFM. A clarification from Sikorsky might be in place. Maybe with the words JimL proposes "through 10-20 degrees".

Also as S. Coyle says "requirement for the FM to be more clear..."

regards
OMP