Offshore Helideck Ops

[SASless]

Current coffee break discussions have revolved around the "preferred" method of departing an offshore helideck or elevated helideck in a twin engine helicopter. One school of thought suggests a level acceleration to best rate of climb airspeed then a climb to a safe altitude whereas the other school of thought is to accelerate at a level altitude until the best angle of climb airspeed is reached, then climb at that speed to a safe height and then accelerate to the aircraft's best rate of climb airspeed. The first method is described as being "better" because it shortens the amount of time the aircraft is within the shaded portion of the Height/Velocity or WAT curve, whereas the second method is thought better because it provides more height above the water sooner, so as to improve the chances of accelerating to best rate of climb airspeed without making contact with the surface following an engine failure.

Major concern for this discussion involves low-height decks (i.e. 50 feet above surface) and the possible contact with the surface which might result while trying to accelerate and fly out of an engine failure at the most critical point of the takeoff...assumed to be just at crossing of the deck edge.:confused:

[Rotorbike]

Hover yourself over to deck edge so the rotors are overhanging. Into as much wind as available. Check all limits OK. Pull power and head upwards, then rotate off the deck. It now depends on if you are day or night.

Day accelerate to 60 kts and climb. Night accelerate slower climbing and accelerating at the same time.

So I suppose both your answers are correct, one for day, the other night.

By pulling power over the deck if anything fails you'll come straight back down on it. Or after rotation if an engine fails just after you aren't going to hit the tail on it.

Most decks are over 100 feet for major platforms. Smaller platforms can be 50 feet. If something fails just after rotation pull maximum single engine, aim at the water and get some airspeed!!! :)

[Shawn Coyle]

Did you consider that the HV curve is a limitation and not to be flown into at all?
Check the flight manual for those two aircraft (unless you have a Flight Manual Supplement for a cofiguration with less than 9 passengers) - the HV curve is in the limitations section.

Second part of the question might be- why not follow the Category A profile?

[SASless]

Lessee here Shawn.....if I creep the thing up to the edge of the deck...or scoot off over the edge...if my memory is anywhere near correct....I am unfortunately in the shaded part of the WAT Chart no matter what I do...and if the aircraft has more than nine pax...or seats for more than nine....and even if I use Cat A as you suggest....me thinks we still have a problem....am I correct in assuming that? Now does the WAT chart only apply to takeoffs over firm, smooth, surfaces....which oceans are not....gosh...maybe there is no legal way to make an offshore takeoff.

Can you enlighten me just a bit more here , Shawn? But of course we must never violate the limitations section of the flight manual while aviating....got any suggestions, flight profiles, weights, airspeeds, or something that will advance this thread, Shawn?

[Shawn Coyle]

There is a difference between the WAT chart limits and the HV. Hopefully you are well clear of the WAT chart anyway - the HV is the one that's difficult.
And you are right, there isn't a lot of help in interpreting the charts.
The 9 passengers or less limitation is on the configuration, not the number of seats you have occupied. You can see this in the change in the HV location on the BK-117 when it goes to a high density seating configuration - the HV curve moves to the limitations section of the supplement. S-76 with the less than 9 pax supplement has the HV curve in the performance section.
The problem is that most of the helicopter community doesn't understand that Part 29 helicopters are supposed to offer the same level of safety as a Part 25 airplane- that's why they are in that category instead of Part 27.
Which brings me back to my original question - why not use the CAT A techniques and performance stuff- the profiles are pretty straightforward, not much of a performance hit, and guaranteed to be able to fly away or land back if the engine fails?

[SASless]

Shawn,

I think the basic response is that operators have to provide as many seats as possible....and Cat A vice non-Cat A translates into 1-2 paying seats less per takeoff. It is also probably fair to state that oil companies usually give mere lip service to safety and revert to the Risk management mode when calculating safety costs....as compared to operational costs.

An example, a rather well known oil company and a large helicopter operator agreed to compromise on reject areas after selecting Cat A standards for their Bell 212 operation. One of the compromises included the approval for the operator to use canals and rivers as an authorized rejected takeoff area following an engine failure on takeoff from land based helipads. The decision was predicated upon the cost of preparing long, smooth, firm, and even landing surfaces for the aircraft. The Cat A takeoff profile itself was altered to provide some semblence of a normal Cat A profile to fit the very short dirt reject areas available. No thought was given to reducing the takeoff weight (based upon seating) during this process. The good news is .....to date there has not been an engine failure on takeoff that required an intentional reject into the water on that operation. The modified Cat A takeoff profile placed the aircraft smack in the middle of the shaded area of the WAT Chart....and was merely an old style US Army confined area takeoff over barriers 150 feet high...that is ...up, up, and away on a nice angle to 150 feet with a reject area as short as 250 feet. The profile seemed to work...but the thought of landing in the water as an approved reject area sure seems unwise to me.

[almost canadian]

Just out of curiosity, if a good amount of power would be available departing the rig, how much vertical distance should you take above the deck before rotating?
What's the common practice out there?

[Nuada]

Any one using a variant of the approach/departure Point-in-space technique?

The departure profile, common in the States in the EMS market, would be to apply sufficent power increments to vertically clear any nearby obstacles.
Then with slight increases in power, and back pressure on the cyclic, work away and back from the touchdown zone, until you reach a height of 150' to 200' above the ground/deck. Upon completion of a power assurance check, gently accelerate the airframe, without losing altitude, until you reach Vy.

It offers an opportunity to execute a sinlge engine procedure back to your departure point with minium ammounts of control input, power changes, and pitch attitude changes.
Perhaps it has more relevance in the confined areas which most EMS types work within, and their lack of appropriate F/L options.

Kevin

[Rotorbike]

Cat A for a 212 from a rather old manual I have in front of me takes you backward and upwards to 160 feet. Initially straight upwards to 40-60ft.

In reality on a good day, hot and heavy your 100% TQ will get you max. 30 feet (more likely 10) above the deck when fully loaded..... and without a wind straight back down on it.

Thats all within weight limits and offloading payload above 22 Celsius.

So as you leave your deck, your tail will clear the deck should an engine fail. Now you have 110-130 feet to get to an airspeed to climb away.

[Shawn Coyle]

I guess I'm a bit surprised by some of things coming out here. First of all the takeoff profiles on a modified Cat A procedure should have been approved by the operating authority not just the helicopter operator and the oil company. Anything less than authority approval will leave you wide open for some pretty damning lawsuits.
I'm also very surprised that a Bell 212 at maximum weight cannot hover more than 30' AGL at sea level in warm conditions. I'll have to consult some performance stuff I have buried elsewhere, but at first glance it appears to me that it should have plenty of power reserve in those cases. Has anyone checked the weight to ensure you are within limits? remember that if you overload the machine, you invalidate the Certificate of Airworthiness....

[Nuada]

Perhaps the difference rests within the element of this technique that you are NOT seeking a flyaway speed with the CatA backup departure.

Once you've cleared the initial obstacles which may impede the capacity to alter the nose of the craft, you gain the ability to alter the direction of the nose of your craft in order to better utilize the relative wind speed available that day.

The wind speed, the more the merrier, actually allows you to better manage your power buffer and back away bit by bit. It is by NO means a rapid response technique.

Should the worst happen, mechanical or met, you have the capacity below 150'(approx.) to execute a single engine approach right back down onto the helideck or LZ dependent upon relative surfaces.

Sorry, not meant to be confrontational, just conversational....
hope this is a better job of restating the concept?

Kevin

[Droopy]

Shawn; I don't know if the 212 transmission limits are any different these days but I spent a lot of time in the mid-1980s in a rather hot and swampy place having to pedal turn on takeoff in nil wind simply to clear the deck, and we were pretty confident about the weight being at or just under maximum. 30 feet wasn't often an option!

[Nigel Osborn]

I'm a bit surprised at the various ideas put forward for this interesting question. Helicopter offshore operations have been in existence for many years and the 212 for over 25 at least. Nearly all companies I've flown for use this basic tecnique.
1. Low hover at front of deck with blades NOT overlapping to build up ground caushion. Position can vary due to deck design & the turbulence you're getting.
2. Apply full available power & climb vertically.
3. At 20 feet radalt (15 feet minimum )for most medium size helicopters, while you still have a POSITIVE rate of climb, rotate fairly positively to about 10 degrees nose down. ( Can vary slightly with c of g )
4. If you can't reach this height, you are too heavy.
5. CDP is the point of rotation. Engine failure before rotation, land back on. After rotation, maintain collective position for transient time if nessary, while looking for VToss, level off and accelerate to VBROC.
6. By having 10 degrees nose down, your tail should be well up and clear of the deck.
7. This works by day or night. In fact you can do this all with your head in the cockpit looking at the instruments and is not a bad method to demonstrate to an unbeliever.
8. This method has worked well for me for over 40 years both in the cold of the Antarctic and the heat of India.
9. Obviously if the helicopter is very light and you have a strong helpful wind, you can modify this. Never make rig work too black & white.
10. Tearing along the deck to gain airspeed is very much a no no.
11. Now watch me be blown to pieces!!:rolleyes:

[donut king]

What's a modified Cat A???

I was taught a Cat A is just that....anything else may be a company approved procedure or a pilots own choice, at his discretion.( Cat B?)

Thanks!

[clearance]

Here Here Nigel... ;)

just admit it, you love'd India?

[Lu Zuckerman]

Being a theorist and not a pilot I open myself to some flack on this but I will repeat what I stated in a post I made a long time ago. This post is in response to the advice given about hovering the helicopter to the edge of the flight deck placing half of the disc in ground effect and the other half out of ground effect.

Many years ago a group of US Marine HRSs (S-55s) did just that only in this case the back ends of the helicopters were hanging over the ocean which was 80 some feet below. When they successively pulled collective they fell backwards one-by-one into the ocean below. A lot of people told me I was full of it and said it was impossible however it did happen and they lost several helicopters in the process. It is similar to hovering above a moving ship and letting the ship move out from under you. When the ground effect of the flight deck was no longer there the helicopter in which I was riding almost fell into the water until the pilot regained positive control.

:eek:

[Rotorbike]

Nigel

Well the technique used here is exactly as you described except we hang the rotors over the edge of the deck. I think you have just explained it better.

At night our preference is towards more level than 10 degrees nose down. Just preference for altitude over airspeed.

Shawn

Max Gross is 11,200 and start lowering from 22 Celsius upwards. From 25 degrees it's about 60-70lb per degree. 38 Celsius will allow you 10280. Temperature, higher of ground or 1000'

Lu

I can understand falling into the water backwards when pulling power with your tail over the edge of the deck but not if you are into wind. If into wind you normally will gain an updraft when at deck edge.

Retiring back behind my stone for cover........

[Red Wine]

Guys........get it right before your OEI in a critical phase occurs....!!!!..or it will hurt.

Good to see old Nigel has found the pump for his wheel chair tyres....

Remember the Oil Platform is a thing to avoid at all costs if you have anything except both engines running wide open..!!!


From a purest point of view,yes the HV curve is in the limitations section....however remember......BHT also tolerate, Winching, Slinging, Longlining and Oil Patform T/o and Landings......

Cat A......geee guys........There is NO place for Cat A is todays Oil Operations......remember what Cat A is designed for..???...

*To ensure a safe OEI reject or safe flyaway after an OEI event for a specific known take off distance.....and reduce the T/O Wt until that performance can be achieved.........and the relevance to Offshore..?.....not much.

A safe departure?.....as per old Nigel......however a 15 nose down or attitude change would be nicier........and there should be no difference for your night verses day technique...remember your Nr droop doesnt know the time of day....nose held down until your airspeed is alive then reduce your nose down attitude......remember its better to be closer with the surface [water] with a healthy Nr and close to Vtoss than at 150 ft with the low NR warning on and no IAS.......farewell indeed.

The suggestion of backing back off an Oil Platform is horrific....in the OEI configatation the oil rig is your bitter enemy....better the water than an impact on the deck [hovering auto excepted]......once CDP is reached at around 15 feet....15 nose down and get out of there.........

OEI before the commited point on approach.....get out of there...overshoot.

Keep your Nr UP.

PS.....Move to the deck edge.......Rotor tips inline with the edge.......not over it........

[the coyote]

I agree with Nigel and red wine. Everything works fine with a deck at 100' or so above the drink. If the deck is lower, say 50' as previously mentioned or on a ship, then you have to ask the question: if I continue to climb vertically to gain enough height to fly away OEI after rotating, how hard might I hit the deck OEI if I abort prior to rotating. Depends on almost everything, and if OEI ditching or hard landings are not an option, pay the dough to load real light....

[Lu Zuckerman]

To: Rotorbike

Although not totally conversant with the entire situation I can only report the facts, as I know them. There had to be a strong relative wind flowing across the deck from stem to stern due to the ships' movement through the water. And, there may have been as you indicated a strong updraft, which may have caused a confusing, wind state with the updraft mixing with the longitudinal flow. This was coupled with the possible lift differential across the rotor disc caused by one side of the disc in the stable airflow while advancing and the other side of the disc in the confused airflow while retreating. If I could, I would place a very large ? at this point. Is it possible that it was due to a flap/blow back situation caused by the strong airflow across the deck (20-35 Knots)?

On the present helicopter carriers (LHA) the helicopters and the Harriers are aligned with the centerline of the ship however on the CH-53s a part of the rotor may be over the side but then again the CH-53s have more than adequate power where the HRSs only had 600-700 Horsepower availavle.

:confused:

[Nigel Osborn]

Rotorbike.
The problem of being at the deck edge is that you lose your ground cushion. Assuming you wish to be at max weight for that flight, you will need more power which by definition is not available. Also depending on the deck design, i.e. is there an accomodation block below?, any wind above 10 knots could give you unpleasant turbulence which by being further back and climbing to 20 feet could possibly keep you out of it.
Red Wine.
Enough of the "old" ! There's nothing wrong with my wheel chair!Using 15 degrees when at max weight tends to lose height faster than you are gaining airspeed whilst still over the deck. Once clear or if light, by all means go to 15 if you have sufficient height to play with.
Coyote.
Using the same technique day and night gives greater consistency of performance plus the non flying pilot will know exactly what you are trying to achieve. Level take offs just because you are low is not the best way. The deck height doesn't really matter; you adjust your weight accordingly to get the performance you need. At low level, speed is generally more important than height. Look at HV charts. Losing an engine at 60 kts at 50 feet is not a problem, try doing that in a 50 ft hover.
If you do lose an engine seconds after rotation, then you will need more than 10 degrees, possibly up to 25 degrees height permitting. At this point you are looking for speed, not altitude.
Bit hard to explain without having a helicopter to demonstrate what I'm trying to say!:D

[Nick Lappos]

All the speculation on best OEI procedures is interesting, but without test or an approved procedure it is all just speculation.

A vertical rise above the deck with a nose down acceleration is the only way to assure avoiding striking the deck edge if an engine quits during the takeoff. How high to go depends on the aircraft, weight and OEI power left, and is not one-height-fits-all.

The most critical time in an elevated deck takeoff is the first few feet, where you most get clear of the platform and netting. A failure there is nearly catastrophic, with a tumble down to the sea likely while just half off the rig. Any procedure that cuts your time there is the best one. We do a vertical procedure in zero exposure operations, which means going up to a height above the pad, then diving to clear the pad lip. If loaded to the wat curve, a failure anywhere during the takeoff results in a landback or a dive away and climb. The critical measurement is tail clearance from the rig during the OEI dive away.

The actual exposure time is only about 5 seconds or so, and the probability of engine failure in that tiny window is truly nil. For the T700 family, the US Army experiences 1 failure each 500,000 hours of operation, so if the 5 seconds of exposure were repeated each hour, and you fly 1000 hours per year, and you have Cat A stay-up ability otherwise, the probability of an engine failure occuring to you during the takeoff exposure window would be about 0.000000000005. Typical rig engine failure experience bears this out.

We debate engine failure, practice for it, work like fiends to polish the procedures, and meanwhile ignore the common fly-into-the-water cause of 1/2 of our fatal mishaps! We are like some ancient religion praying to the engine failure god while each night another beast comes along and steals our best. We don't even recognize his existence!

See the OGP report for a summary of fatal accident causes for twins offshore. 45% is CFIT, 22% Mid air, 22% control problems. Let's debate the real causes, not just the ones we can practice!

http://www.ogp.org.uk/pubs/300.pdf


Nick

[soggyboxers]

I had a single engine failure in a Bell 212 just after rotation, going off a helideck on a drill ship in Egypt many years ago. It was around 38 degrees C and I think I was around 10600 lbs. We used to use the technique of rotor tips just inside the deck edge, pull hover torque + 15% (or full power, if less) and rotate at 10 feet or when RoC started to fall. The engine failed just after rotation, then caught fire and the deck was around 50 feet elevation. I used nearly 15 degrees nose down, avoided the deck edge but was still only just over 30 knots at around 10 feet. However, the good old 212 did mange to start climbing shortly thereafter and got us safely back to shore. The Nr was pretty low though (around 85%). I don't think a low inertia rotor rotor machine would have fared as well.

[Nick Lappos]

soggyboxers,
That was the proverbial worst case failure all right. What was the cause of the quit?
Nick

[SASless]

Shawn,

I described the "modified Cat A" takeoff in my post and for a quick repeat....the operator and the oil company mutually agreed to the modification and led the local DCAA to believe all was well. Thus your concern with compliance with the letter of the law was taken care of.

The salient point of my post was to take issue with the idea that accepting a rejected takeoff to a river or canal constitutes knowingly and with malice aforethought....what would in any other situation be known as an "emergency ditching".

That decision was predicated upon the customer's objection to spending the money required to bulldoze and grade the appropriate area for reject areas while at the same time claiming to be using Cat A performance.

As a Test Pilot and Instructor of Test Pilots, I would think you would be more immediately concerned with actual performance versus theoretical performance, and constructing your test flights to conform to test parameters in order to be able to determine if the aircraft is operating as designed or expected.

To declare the use of rivers and canals as reject areas flys in the face of the normal criteria used to define reject areas....ie..firm, smooth, even surfaces.

Last time I checked...4-5 degrees above the equator at sea level and an average temperature variation of 30 degrees C plus or minus 10 degrees...water remains unfirm .

So, Shawn....what's a working pilot to do, when confronted with such issues....letter of the law met, company SOP and Ops Manual dictates the procedure, checkrides require compliance, and the whole time, both customer safety staff and company safety staff sign off on the procedures?

Or...am I completely missing the point and intentional landings in a river or canal while conducting Cat A operations with emergency float equipped aircraft are both safe and acceptable under the constructs and criterion for Cat A operations? (as defined by that particular DCAA, oil company, and helicopter operator)

[Nick Lappos]

Sasless,

The point of view that "knowingly" operating without full Cat A capability is some how wrong or unethical is baseless, and Shawn (a friend and a very capable guy!) knows that too.

Operating rules are in place that allow limited exposure to engine failure in virtually every place on earth (does anyone know of a requirement for Hard Cat A in commercial oil operations?)

If a sudden requirement for hard Cat A were implimented, the operating world would stop, and safety would not improve to any measurable degree. There is much controversy brewing as the JAR Ops requirement clock ticks down, and also some rumor of ICAO adaption of that standard (these rumors are not true).

Engine failure is not our problem, not according to our history, and the blind implimentation of hard Cat A criteria would actually hinder the improvement of safety (because it would spend money and regulatory horsepower where it is not needed, and divert same from where it is.) See my above post for the pointer to the real data.

Keep plugging, Sasless, Shawn, let's rumble!!

Nick

[SASless]

Nick,

I understand your concerns about the adoption of Cat A requirements by ICAO and JAA. My position was....and is....the claim was to be operatiing under Cat A when in reality the decision to withhold the proper reject areas in actuality made the operation non-Cat A. The point being....call it what it really is...non Cat A with all that means.

With the JAA/ICAO crisis coming....maybe the old Wessex with twin Gnomes will become in vogue again!

[Nick Lappos]

SASless,
There has never been any deception about Cat A procedures and exposure windows at rigs, the issue has been known and understood since the beginning by regulatory agencies, operators and manufacturers. Welcome to the group, Sasless! There were even modified Cat B procedures to allow zero rate of climb enroute, and add a few hundred pounds more payload, with full CAA approval.

What I am concerned with is the blind adaption of a requirement because it is "complete" or "neat" without a real justification, while ignoring the real causes of accidents (why not mandatory EGPWS?)

So, let's declare all offshore helos obsolete, toss them out and replace them! I am sure that money spent on new helicopters is just laying around out there, unspent right now and available. It will not mean any reduced operating budgets, fewer aircraft, fewer contracts. It will not make fewer jobs. Of course, all that is not true, it will cost all other parts of the industry to suck up the differrance. What can be said is that it will NOT cause any measurable rise in offshore safety. That is guaranteed.

It is in the best interest of my company to support the new operational requirements, since the S-92 is "hard" Cat A from a rig with full pax and enough gas to go about 350 NM with JAR reserve.

[soggyboxers]

Nick,
My engine fire and failure was caused by the engine oilf filler cap coming off after the retaining nut on its locking plate sheared off. I'd been flying for about 3 hours on a crew change at the time.

[jbower]

Under FAA we are allowed to violate the H/V limitations during an offshore take-off or landing by 14 CFR 91.9(d). PHI has had the H/V limitations removed for all Transport Category Rotorcraft (Part 29) at PHI.

Jack

[cpt]

I would like to have your opinions about an offshore production platform helicopter refuelling installation.
To make it short,the flare on this rig, is obviously too close from helideck and its fueling system, the radiating temperature on the deck surface is commonly measured at 47°C and is about the same on helicopter skin after a short st.by. Depending upon the wind, small drops of burning crude oil spill everywhere in the vicinity, a shield of (salted) water doesn't change these figures a lot.
Untill now we are not happy to approve this new refuelling installation and to stand by here but we cannot find any regulation dealing with this matter.
The platform's engineering service keeps telling us there is nothing wrong in their design.
Does somedy here knows something about this ?

Waiting your answers before everything ends up in ashes

Thanks !:{

[Old Man Rotor]

Look up ICAO Annexe 14.................

If you have an incident/accident.......please be assured your Insurance Company will know every aspect of Annexe 14 that you decided not to enforce.

[cpt]

Thank you for your answer "old man rotor" but on the ICAO 14 doc I have, there is nothing about refuelling installations and minimum distances from open flames ( as with a flare). It's just our common sense that tells us it's too close and too hot for a safe refuelling.

[Old Man Rotor]

Ok....give me a few days and I will hunt the reference up for you......

However I can't remember any reference to the flume of fumes, heat, flares or smoke etc.....

But certainly to the 180 degrees approach and 150 degrees 5:1 drop off ratio on departure....

Also the splay outward from the side of the "D" value.......lights, markings, fire equipment etc.


The UK have their own reference to ICAO Annexe 14.....from memory its CAP 243 or 432.....maybe 342...Bingo.!!

I will do my best to dig into my files for you.

Can anyone help with the correct UK CAP??

[verticalflight]

CAP 437 - Offshore Helicopter Landing Areas - Guidance on Standards

I'll come back with more info shortly.

[verticalflight]

CAP 437 states that when helideck temperature rises by 2ºC over the ambient temperature, the BHAB (British Helicopter Advisory Board) should be notified.

BHAB is the body in which the CAA discharges its regulatory responsibilities regarding offshore helidecks. Therefore, BHAB is the authority in this respect.

I used to inspect helidecks on behalf of BHAB, and in most cases when there was a rise in the helideck temperature it was due to hot exhausts. In any case, there was never a difference greater than 4ºC. In such circumstances the procedure in place was that radio room should pass on to the helicopter both OAT and helideck temperature, so that the crew were aware of the possible loss of performance once close to the deck.

CAP 437 also states that cold vent, exhaust and flare systems should be designed to terminate and discharge at a location on the installation as far from the helideck environs as possible. The potential release volumes, flammable concentration, and dispersal characteristics should be quantified, so that -if required- a 'no fly zone' around the hazardous area could be applied.

By the sound of it, the standards in the installation you mentioned above are nonexistent.

If you need more information about CAP 437, please let me know.

PS: There is a set of comprehensive studies (M E Davies - 1977 to 1979 - Local atmospheric environment of offshore installations), which was used at the time of amending CAP 437 in 1998. I don't have access to it now, but I guess it could be a very valuable source of information.

[MaxNg]

Cpt

Send me your e-mither adress and I will let you have acopy of Civil Aviation Publication No 437 (CAP 437)

What is the geographical location of the helideck (governing Authority)?

[cpt]

Many thanks for your answers, my email is [email protected]
This helideck is located in the Gulf of Guinea and the governing Authority here doesn't say much about helicopters in general, therefore we use to comply with ICAO or country of registration regulations.
Until now we don't intend to use this refuelling facility but it is embarassing not to be able to show a regulation who could help our customer to solve this problem.

[Old Man Rotor]

Just be aware that ICAO 14 gives guidance to all member states [countries]...........

States can then vary the standard Annexe 14 with some of their owns rules and standards.....hence the UK call their equivilant of Annexe 14, CAP 437. The US will have theirs and so on and so on....

By the sound of your area of ops.....who knows what standard would apply.

[peter manktelow]

POINT IN SPACE (offshore) IFR approach

(Offshore Cloud break procedure)

We currently have a small dilemma here in China which I would like to see rectified. We have CAAC approval for the standard NDB/ARA approach to the rig , albeit to slightly higher minima. This serves us well for the outbound trip.

Inbound , if the weather is really ugly then we have access to an ILS at destination but it requires some extra off route flying time.

Our track from the field to helibase (which is for all practical purposes , on the beach) , takes us over a small island located 5 miles offshore (highest point 600 feet)
Invariably ATC has us descend to 1000 feet and report that we have this island in sight before he will give us clearance to make a VFR approach. Fair enough.

The “ugly” weather here in the tropics is very rarely cloud base below 500 feet. (Visibility is another matter. When the rain starts it can drop the visibility down to damn near zero.)

For those days when the Wx is not ILS ugly (but am in cloud at normal cruising 2000 feet) , I would sooner letdown , on track to say 500 feet but 5 miles back from the previously mentioned island and motor in to say 2 miles (Chinese VFR requires 1.6 nm vis). If I cannot see the island at this juncture then it is time to turn around and request clearance to the ILS.

This let down as mentioned above would be with the aid of NDB , DME , GPS and Wx radar.

When I was with Shell Brunei many moons ago , they had a “point in space” approach that allowed just such a let down.

Now here is my request from all you folk out there. I have a better chance of getting a CAAC approval IF I can show that other civil aviation authorities regularly give such approvals to IFR heli ops.

Could you please send me your ideas but better still your “point in space” cloud break procedures if you have them.

Tanks muchly

Peter
:8

[Eurochopper]

Here on the North Sea (& allowed by JAR) we have an en-route letdown procedure. I don't have the books in front of me but I am fairly sure the requirements are: at least 10 nm from land (as determined by wx radar), an expected weather of at least 600' cloudbase and 4km vis. If we are not clear of cloud by 500' we must give up and go IFR.

By night its 1200' and 5km for reasons I have never understood! ( - what's the difference between day and night when you're in a cloud?).

If I have got the figures wrong, no doubt some other N Sea chaps will let me know :oh:

[cpt]

Peter,

Are you talking about an "enroute off-shore let-down" or about an approach procedure ?
If I understand well, you just need to transition from IMC inbound cruise at 2000 feet to a formal VFR in order to avoid full IF procedure, and you would like to make this procedure official with local authorities, as for instance a determined special VFR helicopter corridor from this "point in space".

[peter manktelow]

CPT....right on the money

Eurocopter...thanks....grist for the mill

Peter:8

[cpt]

Peter,
I have had to face a similar problem in an African country where helicopters were allowed to operate VFR only.
This, beeing not compatible with an offshore scope of operation, we had to offer local CAA officials a trip to Aberdeen to make them believe helicopters could safely fly in clouds at night and, when adapting speed, in reduced visibility.
Back home, they worked out an "helicopter SID and STAR" , separated from "planked-wing" procedures, and allowing us to offshore depart and arrive at transition altitude in their controlled area.
The next stage would have been to make official a lower altitude than transition altitude (2600') over off-shore sectors and eventually drifting to "reduced visibility helicopter lanes" to get completly rid of IFR procedures (not very confortable in stormy conditions with "adapted" fuel reserves and a "virtual" divertion)
But this scheme sadly never evolved, because controllers becoming aware of off-shore helicopters equipment and crew experience, cleared for a "visual approach" most of the time when requested by a crew.
Reporting points on theses SID an STARS where determined on VOR/DME use.
But, as a matter of fact, helicopters are at ease in the shadow area between this cristal clear part of regulations and the darkness of unlawfull chaos (sometimes they even feel better in chaos !

:E )

[reynoldsno1]

New Zealand has published GPS NPA to offshore installations, though they are vaialable to "approved" operators only. The MAPts are offset 45 deg from the platform at 0.9nm. The OCHs are in the region of 250-290ft with vis. of 2000m required.
The operators also have NDB/ARA procedures in their Ops Manuals. With radar altimeter, the minima are even lower (vis. down to 1500m - 1000m under certain conditions)

[GLSNightPilot]

In the U.S. Gulf, we don't normally do approaches over the water inbound, although we could. We have regular GPS approaches on land to our bases, with the MAP in a clear area, and VFR transition to the heliport at approach minima.

Offshore, we do either an OSAP (Offshore Standard Approach Procedure) or a HEDA (Helicopter Enroute Descent Area) procedure, depending on the situation. HEDA's are points that have been checked & have no obstructions in a 4NM radius circle, and we can descend to 400' as long as there are no radar targets. This should get us into VMC, after which we proceed using offshore VFR minima, which is 300'/2mi for multiengine helicopters. These are used when there is no weather station available, which is most of the time in my area. OSAP's require weather, and are flown to 200'/.7mi to a target (300/1 at night). What you are contemplating is likely our HEDA, and has to be at least 5 mi offshore here.

[gnow]

I wonder if there are operators out there who allow the pilot not having the rig obstructions on his side to do rig approaches and take offs. This has always been a point of debate with my friends as I feel the pilot who has the obstructions on his side should always do take offs and landings for the simple reason that you get a better judgement of the approach and should you be unlucky enough to get a single engine the chances of a safe landing is much more.Most of the captains with me practice a 50% captain and 50% co pilot approach. We practice a straight in approach. Is there any JAA regulations to this?

[Chopper Jog]

Hallo there,

The question you have to ask yourself firstly is: "What if.........?" For example: If there is an engine failure on departure, which pilot will have the best view of all the obstructions? Furthermore, if the emergency occurs before the committed call, will the handling pilot have sufficient visual cues for the reject?

The pilot not having a clear view of all the obstructions on the approach and arrival path is certainly not in a position to assess the potential hazards associated with the facility (rig, ship, etc). Regardless of the cockpit gradient or experience levels, the pilot that will ensure the safest arrival/departure from a facility is to do the flying.

There are other instances where both pilots can do the approach/departure, like landing on a gas ship where the deck is situated in such way that the approach and departure paths are clear from either side.


Hope that answered your question and concern.

Cheers,

CJ

[helmet fire]

Why not design and use a GPS approach? I believe design criteria are available from organisations like CASA in Oz.
If it is a matter of money for equipment (TSO GPS) then perhaps you could justify cost of aquisition with the amount of extra flight time required for the ILS procedure.

Also - please dont take this the wrong way as it is hard to get the full picture from your question - but would it be better to have the approach to along a track abeam the island rather than directly at it? (even with a radar image)

[GLSNightPilot]

IME, over here it's up to the captain. The company doesn't require any particular procedure, as long as it's done safely. Most captains I know do have the pilot with the obstructions on his side fly the approach, & that's my usual procedure, but nothing is written in stone, nor should anything be. That's what a captain gets paid for - judgement.

[sandy helmet]

Usually its the pilot not sipping his coffee or eating his cream cake/donut that would make the approach/take off.

[peter manktelow]

GLSNightPilot....agree with you one million percent....it still amazes me that some of our legislators think they can bring about absoluet air safety by creating a new law or rule every time something goes wrong.
Lets not get legislated out of our command.....

good thread

generally I agree with the initial idea but there are some times when you just have to do a cross cockpit landing...not nice , particularly if it is the S76.

Peter
:8

[peter manktelow]

helmet fire....hey , no such thing as a bad idea...I like it....thanks muchly

Peter
:8

[Mars]

Peter

JAR-OPS 3, at amendment 2, had text added to permit offshore letdowns. This was done for two reasons: To facilitate offshore let-down procedures that had been in existence for many years on the North Sea (and elsewhere);

To facilitate the use of coastal heliports (alleviation from the requirement to nominate an alternate/carry alternate fuel - when operating in accordance with guidance in the advisory material).Text to permitJAR-OPS 3.365 Minimum flight altitudes
(See IEM OPS 3.250)
The pilot flying shall not descend below specified minimum altitudes except when necessary for take-off or landing, or when descending in accordance with procedures approved by the Authority.

Amdt. 2, 01.01.02Alleviation from the requirement to specify an alternate when returning IFR from offshore JAR-OPS 3.365 Selection of heliports

...

(c)For a flight to be conducted in accordance with the Instrument Flight Rules or when flying VFR and navigating by means other than by reference to visual landmarks, the commander shall specify at least one alternate in the operational flight plan unless:

(1) The destination is a coastal heliport (See AMC OPS 3.295(c)(1) and IEM OPS 3.295(c)(1)); or

...
Alleviation from the requirement to specify an alternate
AMC OPS 3.295(c)(1)
Selection of Heliports
See JAR-OPS 3.295(c)(1)
1 Any alleviation from the requirement to select an alternate heliport for a flight to a coastal heliport under IFR is applicable only to helicopters routing from offshore, and should be based on an individual safety case assessment.

2 The following should be taken into account:

2.1. Suitability of the weather based on the landing forecast for the destination;

2.2. The fuel required to meet the IFR requirements of JAR-OPS 3.255 less alternate fuel;

2.3. Where the destination coastal heliport is not directly on the coast it should be:

a. Within a distance that, with the fuel specified in 2.2. above, the helicopter can, at any time after crossing the coastline, return to the coast, descend safely and carry out a visual approach and landing with VFR fuel reserves intact, and

b. Geographically sited so that the helicopter can, within the Rules of the Air, and within the landing forecast:

(i) proceed inbound from the coast at 500 ft AGL and carry out a visual approach and landing; or

(ii) proceed inbound from the coast on an agreed route and carry out a visual approach and landing.

2.4. Procedures for coastal heliports should be based on a landing forecast no worse than:

a. By Day. A cloud base of DH/MDH + 400ft, and a visibility of 4km, or, if descent over the sea is intended, a cloud base of 600ft and a visibility of 4km.

b. By Night. A cloud base of 1 000ft and a visibility of 5km.

2.5. The descent to establish visual contact with the surface should take place over the sea or as part of the instrument approach;

2.6. Routings and procedures for coastal heliports nominated as such should be included in the Operations Manual Part C - Route and Heliport Instructions and Information;

2.7. The MEL should reflect the requirement for Airborne Radar and Radio Altimeter for this type of operation;

2.8. Operational limitations for each coastal heliport should be acceptable to the Authority.

Amdt. 2, 01.01.02The text in the first quote is the alleviation that you require. Offshore letdown procedures are contained in Operations Manuals of offshore operators.

[Mars]

PM

On what occasion (and with what justification) would you just have to do a cross cockpit landing?

[Twisted Rigging]

MARS

Single pilot ops. perhaps!

[peter manktelow]

Hi MARS

Pingle silot is one example (thanks Twisted Rigging) although this is almost a thing of the past with most oil companies world wide now requiring two pilots.

I agree that 99 % of the approaches should be flown by the pilot with the obstacles on his side. I just don’t want to have it written in cement that I must always have this pilot do it. I just hate it when a regulation or rule is imposed where good judgement is what is required.

I am going to send this thread to a good buddy of mine. I seem to recall we hacked this subject to death in Bombay many years ago and again in Brunei with a check/training pilot. Anyone out there recall flying onto the Sagar Samrat ? The deck was so small and awkward that the offside pilot (as PF) could see the deck edge which was where he had to place the gear footprint whilst the PNF (closest to the obstacles) kept an eagle eye on those obstacles. He could not see the deck edge.

I do recall the odd time when I was the offside pilot with a partner in the other seat who’s experience was not up to par. I felt more comfortable doing the approach myself….so did he.

Of course the S76 is just the worst machine for a cross cockpit approach/landing however the 61 is not too bad , the 212 gives good visibility and the AS355 is single pilot anyhow. (if you hadn’t guessed , these are the 4 multi engine types I have…)

Another factor is the type of structure that you are landing on. We had “double” platforms in Thailand that had obstructions both sides and the overshoot sometimes favoured a PF who had the lesser obstacles on his side…..many variables……

I can think of a number of accidents flown by the pilot who had the obstructions on his side and he still ran into them !!!….now to be fair , there were probably other extenuating circumstances…and perhaps that is subject matter for another thread.

This type of discussion is all very , very good value…..

[IHL]

Peter:

This goes back quite a few years; a company I worked for had a contract for offshore surveillance with the Department of Fisheries and Oceans, Canada. We had an ops. spec. that would allow us to decend to 300 feet over the water. We had to be more than 5 miles from shore and verify our position with 2 independant means i.e. LORAN and RADAR .

It worked well.

[Outwest]

PM.... Pingle silot ? At what time of the day and number of rums did you make this post? Yes, this debate is about as old as the chicken and the egg. If memory serves (and that is starting to go now as well) The check pilot in question was of the opinion that during a OEI overshoot just prior to COMMITED, that the pilot with the derrick on his side was in a better position to see the edge of the deck (the side the pnf is on) for the escape. That was where I disagreed. He would have no view of the water, which in my opinion was a far greater obstacle to avoid. I pointed out that in mountain flying (which the check has no experience in) you ALWAYS approach so that the escape route is on your (PF) side.
Now, having said that, I firmly believe that in normal day to day ops, the landing pilot SHOULD, not SHALL, be the one with the obstacles (ie. derrick, railings , crane etc.) on his side during the landing. This to preclude bashing the tail rotor or other bits into the rig during postioning for touchdown. You will notice I said SHOULD, as PM stated there are occasions when it is safer to do it the other way (very inexperienced co-pilot comes to mind). It is, has been, and always will be the Capt's ass on the line here. The whole idea of a CAPTAIN is to use his knowledge, experience and good judgement to bring everyone home safe, not create robots or worse yet "press the green button now....get a banana" approach. Ok, done ranting. And I haven't even had my first rum yet! Over to you.

[Mars]

PM

If I could discuss some of the facts and assumptions made in your email:

I sensed in the original post that the question had been asked because a Captain had exercised discretion and taken a cross cockpit landing. I saw the thread as an interesting discussion based on that assumption (that assumption could have been wrong and the thread is no less interesting for that).

(The use of his also implies her.)

Let’s get one issue out of the way - this is a thread about two pilot operations and the comments about single pilot are not therefore relevant - let’s leave them for another thread.

In my opinion (with some experience), all approaches (at least in the final stages) should be flown by the pilot with the obstructions on his side - as indicated by Chopper Jog. The only exception could be an occasion when a risk assessment indicates that an alternative would be less risky. (No rule required this is a matter of good judgement and CRM.)

Hopefully, most decks have a bum line or a marker where, if the pilot position is correct, best obstacle clearance is obtained (and maintained). A deck where a pilot has to eyeball the edge of the deck to ensure the wheels are on the deck is an unacceptable risk to the pilot, operator and the oil company. Even if this is the case, the PH can be conned to the safest position by the NHP whilst ensuring that clearance from obstructions is maintained.

No operator should allow a situation where a pilot in a two-pilot crew is not up to par - except in the case of sudden illness. Even if that is the judgement of the Captain, taking control and doing a cross cockpit landing does nothing to assist in the development of the other pilot, or improve the state of mind of either.

Whilst your comment about pilot view in the S61 v the S76 is true, a cross cockpit landing in either could pose an unnecessary risk.

I too can think of a number of accidents where a pilot ran into obstructions on his side - none of which would have been prevented by a cross cockpit landing.

For the question raised by gnow on straight-in approaches, no there is no JAA rule precluding it but I recommend a visit to the accident investigation web sites which are replete with example of approaches which ended with the pilot striking the tail, ADELT, tail rotor etc.

If you work for a JAR-OPS operator, you might read JAR-OPS 3, IEM OPS 3.517(b) - Procedures for continued operations to helidecks (pages 2-H-5 and on) which gives guidance on most of the issues of deck landing and take-off - not the least of which is the preservation of options that would be closed to the pilot on a straight-in approach. Remember that most of these landings are in Performance Class 2 with exposure.

An enjoyable and important thread!

Mars

[gnow]

There has been much debate on the "correct " angle of approach on to an offshore platform. What would be an ideal angle of approach in a nil wind situation that will allow a safe single engine landing to the deck?

[GLSNightPilot]

You may get a lot of answers to this, but my method in an S76 is to put the pitot tube on the far edge of the helideck and keep it there. In a 412, I do close to the same, but I generally try to just be able to see the far side over the glareshield. I tend to sit higher than many other pilots, though, so this may not work for everyone. I suspect, from the seat adjustments I have to make when I follow other pilots into the aircraft, that many of them couldn't see the pitot tube at all.

[thechopper]

:8
GLSNightPilot
And how many safe single engine landings have you done out of this positioning?

Just asking.
:confused:

[Red Wine]

GLSNightPilot was correct, there are a heap of attitudes on this subject, all with some element of truth to it.

I must correct/clarify one part of your post.....My philosophy is never to land on an offshore platform OEI, and to do everything possible to avoid that occurring.

And why??

1.. Apart from a small handful of heavy twins, SA332L1 & 2, B214ST, not sure about the S61, no other twin has the certification to hold OEI onto Offshore Platforms, in other words other helicopters which include the two mentioned by GLS can not undertake OEI platform landings and survive intact every time. There is normally heaps of discussion on my last statement, including SIM justification that it’s possible. From my experience an Instructor can always have you crashing a high % of the time when trying to undertake this in practice....don't give yourself false expectations.

2.. An Oil Platform is a hard dangerous place to go at the best of times, yet alone OEI. Avoid them like the plague in an OEI in a medium twin.

3.. The owner of the Offshore Platform would normally not appreciate you landing OEI on his/her platform when you could quite easily take the passengers home with you. A platform worth a few hundred million dollars and 100+ POB verses an old medium helicopter worth one or two million and a handful of POB says it all.

[Now if your working where onshore alt fuel is not carried, then perhaps you should take swimming lessons]

Gnow....To your question.....

At all stages of your approach, have the mindset that you are not going to land on that platform until that point in space when it becomes impossible to avoid the platform....and that point is called "Committed".
Any OEI prior to "Committed" then pull 2.5 mins OEI power and VTOSS and get out of Dodge.
After "Committed" its always possible to arrive onto the platform OEI, because you have planned the approach.
The aiming point should be the side of the helideck closest to your side of the approach, which means you can leave the "Committed" call to a later point in space than if you aimed at the centre of the circle.

Whilst this approach resembles CAT A profiles...it is not CAT A [but that is another topic]....

Whilst GLS utilises a fixed aiming point of his aircraft, this style of approach is not sound in all conditions.

In Nil Wind and a hot humid day, you will have your work really cut out for you in an OEI configuration....if you are low and slow, then you will fall short for sure and not have the power to continue to the deck edge, your ITT, N1 will be accelerating up to their limits with the Nr decreasing, and you pulling more power to make the edge......don't go there, plan your "Committed" position with AEO and fly to it.

If you are on a High Approach, then you now have the same problem caused by different elements, but the result will be the same on a hot windless day with an OEI , large power demands to arrest a descending helicopter causing ITT and N1 increases and a reducing Nr. Bet you can't do that in practice without wrecking something....at least most of the time.

So don't get yourself in those positions in the first place......I suggest getting into the final approach at 80 knts and 500 feet Rad Alt and then aiming to be at your "Committed" position AEO at around 15 knts and 15 - 20 feet above but to the edge of your platform.

Then you should survive and your aircraft not damaged. [Fingers crossed]

[Chopper Jog]

The luxury of flying offshore at night in rainy conditions.

It is great to be a helicopter pilot, especially when we dont fly in a controlled-runway environment with approach aids and lighting such as an ILS, VASIs, etc.

The way I view approach angles offshore will be based on a combination of variables, such as the type of helicopter you fly, layout of the offshore installation and the prevailing weather conditions.

I have seen the different approach angles in flying a Super Puma and S76, especially when looking at the performance during OEI operations (simulated of course). So what I am saying is that with a Super Puma's performance one can commit at a much later stage of the approach and be assured a controlled landing at the bottom (Good OEI performance at most weights).

In the case of the S76, the opposite holds the truth. I prefer a higher approach angle to give me the extra margin for safety and to increase my flyaway chances and once committed, it will at least get me on the deck without undershooting and clipping the edge of the deck (Poor OEI performance at all weights).

Since I use to be a rugby player, this picture works quite well for me. Regardless of your height and distance from the platform, once the helideck lighting opens up in the shape of a rugby ball or almond, that is the approach angle I fly down towards the deck. It sounds basic, but it works for me.

Best wishes and safe flying for 2004.

Cheers,

Chopper Jog

[gnow]

A friend of mine went for his simulator check on the S61N and was told that normally the approach angle is about 30 degrees. So for a 22m deck when we cross the deck edge we should be theoritically 40 ft above the deck edge (using sine,cosine formulas). I tried this but it looks rather low.However, I find a lot of pilots in trying to do steep approach ending up in a high hover over the deck.

[Steve76]

I'm with GLS on this one.
Steep is good, shallow is bad.
You really need to have your rate of decent and airspeed under control for the nil wind, hot approach. Otherwise it is not the engine failure but the crane at the end of the deck that smokes you.
Post your committed point you want to guarantee to land on the deck and not the kitchen.
I also sit high and use the pitot's as a lead on the 76. Its worked perfectly for the last 4000 odd offshore and onshore landings.

Plan to arrive alive :hmm:

[Chopper Jog]

Approach Angle:

CHC Intl uses 500ft/0.75nm

Landing on a deck of 100ft above sea level, this will give you a 5-5.5 deg approach angle. I think the 30 deg angle is close to an autorotation if you compare it to a normal ILS of 3 degrees. I also believe that the Norwegians have a Copter ILS that is calibrated at a 7-degree approach angle.

At least the 30-degree approach angle will give you sufficient height if you decide to use that. Safe flying!!

CJ

I have used the TAN Formula whereby the distance over the ground is 0.75nm = 4500ft (a) and the height above the deck is 400ft (0), this give the approach angle (Q) of about 5 degrees

Correct me if I am wrong.

[Hilico]

In an earlier thread about helideck landings, it appeared that there is a 'reference position' in the S-76 (and for all I know other types) which guarantees the eye height of the pilot - one gets in and fiddles with seat adjustment until the standard sighting cues are met.

It sounds as though the pitot is invisible from the reference position.

Can anyone explain where I'm going wrong?

[Hilico]

Nervy, Rotorheads is aimed at pros (it's in the forum description). Therefore they don't have to speak English; they can talk shop.

I'm not a pro myself (in fact I'm barely even an amateur), but I read all the threads and try to work out as many things for myself as I can. It helps that I subscribe to JAR-OPS3 (the manual that covers AOC Helicopter operations); and you can bet the pros (certainly in Europe) have very easy access to that.

In this case, OEI is 'One Engine Inoperative'. By contrast, AEO is 'All Engines Operating'.

[Red Wine]

Mr. Shelfish is correct, and a full definition.

"Is that speed at your 2.5 minute OEI power setting that will ensure a ROC [Rate of Climb] of 100 feet per min" in ambient conditions.....look in you RFM. [Rotorcraft Flight Manual]...it should be stated.

[dudeunit]

I agree with all post concerning the steeper approach angle is desirable. In the the event of an engine failure after your "Committed" or "LDP" flying the B412 or 212 with PT6-3B twin pack I like to have my rotor disc cross the deck at 55% Xsms torque or less. This will leave in reserve up to 18% ENG TQ available for cushioning with your operating engine on a IAS day. But, with the 3B's your limiting factors will be ITT or N1. (Not sure if I care at that point) Just as long as my feet are dry.
This technique is difficult and uncomfortable on a no wind day so I tend to be a bit slower with no wind. Placing more trust in Pratt and Whitney.

As far as sight picture a high seat position makes it easier to fly the steeper angles by keeping the deck in view.

Somebody mentioned settling with power which should not a factor as long as your not in a downwind condition and leaving your vortices behind you. Remember, you need all three factors to settle with power. ROD 300 fpm or greater, 20% to 100% power applied and zero near zero airspeed. By the time you have near zero airspeed you'll be IGE.

This was an interesting post and and I appreciate the exchange of ideas and techniques. There is a lot of ambiguity and many ways to skin a cat!

Cheers.............

[thechopper]

how many of all the posers (sorry, posters) on this thread have done it. OEI that is; I haven't.
And a happy new year to all of us and let's hope we do not have to do it.
Happy Landings OEI or AEO from the Northsea.:} :}

[Wayne Jenkins]

In a previous life, I was operating out of Juhu Airport, Mumbai, India with 6 x B412's on Offshore Operations.
I guess the feeling amongst the majority of the national flightcrew was that there was far to much emphasis placed on OEI and other emergency aspects of flying.

That belief soon changed, after an OEI developed when a Senior [Now retired ] Captain and a Senior F/O were approaching a Jackup Platform.

From the transcript of the CVR [including the engine noise from the cockpit microphone], its was obvious that their OEI approach commenced simultaneously with the First Officers [Flying Pilot] "Committed" call.

The end result was that the heavy B412, skidded about one [1] metre on the deck, and came to rest about half way between the deck edge and the circle, just where the Flying Pilot was aiming for.

The remaining engine suffered no transient excursions, which was verified by the electronic monitoring equipment installed.

"Thecopper"...that is one that I have witnessed close up, and there have been others in Australia over the years.

Happy New Year to you all.

[GLSNightPilot]

While I've done it countless times simulated (both in the aircraft and simulator) I've never had an actual engine failure. I keep expecting my first one on every flight, but it hasn't happened.

If I have any advantage, it's that I'm flying an S76A++ with plenty of power, and usually relatively lightly loaded, so I can often hover OEI. That partially makes up for doing it in the dark. My method works in training, but I've never had to try it for real.

[snoopymagnolia]

There has been one OEI recovery to a platfrom following an engne fire indication in Bass Strait. Ross M completed a safe OEI landing onto a platform after shutting down one of the engines in a S-76C.

Cheers

[Avnx EO]

Need some good user input...

Looking for folks who operate off oil platforms or in the Canadian North.

Question is whether you still actively use "DG" (unslaved mode) for your compass system. Given GPS would you miss it if it were not there? (i.e. mag slaved mode only)

I've been told that folks flying to oil platforms switch to DG mode when they get close to the platform (because all that iron affects the compass). Is that true? How close do you switch?

I've also been to told guys in the Canadian north use DG mode (because of proximity of the pole makes mag slaving unworkable), and instead set the DG based on ground reference or GPS track.

The issue is that there is new technology coming into vogue that is destined to replace the old gyro systems, This technology has allowed fixed-wing aircraft to now be offered with really cheap glass cockpits. A key ingredient of the cheap system is an attitude and heading sensor that uses MEMS technology (micro electro-mechanical sensors), but the problem is that these "gyros" don't remain stable very long when they lose their slaving. As a result, most of the fixed-wing systems using this technology no longer provide a "DG" mode. Question is whether losing the DG mode is acceptable for helicopters.

I've been told that people have worked around this by flying GPS track, and that the new magnetometers are less affected by declination angle and so you don't get the attitude based compass errror in the far north like you got with the old systems.
Other people have told me that it's only the old farts who still use DG mode. :ouch:

The guys flying CAPSTONE stuff in Alaska may have some opinion on this as well. Since the technology was developed for the CAPSTONE program, but is now being used in stuff like Garmin G-1000, Honeywell APEX-2000, Chelton Flight sytems, and the system on the new Eclipse (Avidyne). Given the cost and reliability of the MEMS, it will eventually displace traditional compass systems.

---- so the change is coming... is it going to be a problem???

Thanks in advance


Avnx EO

[Bivar4]

Although all ships, platforms & rigs are of Metal/iron, not all influence the compasses the same way.
We had a FSO that would upset all compasses by more than 90º. Switching to DG before landing would allow a quicker reset after take-off. Some instalations would not upset the compasses at all.

If you forget to check your gyro after T/O, youd could be embarrassed when finding your self several degrees off course :\

[Gomer Pylot]

Some pilots offshore switch to DG mode after landing, and then switch back after takeoff. Depending on the platform and how long you're there, your heading indicator can be pulled off, sometimes by much more than 45 degrees. It's a tradeoff - switch to DG and not have it pulled off, and then forget to switch it back and have it drift off over time, or leave it in slaved mode, and reslave it after takeoff. I tend to just leave it slaved, because it's hard to know how much it will be affected, and assume it will be off after takeoff. The PNF just calls out track from the GPS, and reslaves the compass once we get stabilized on a course. It's a PITA to have no idea which way you're going, especially in the dark, other than reading the track from the GPS, but we deal with it the best way we can.

[Sailor Vee]

On the North Sea, the compasses are set to DG as part of the 'finals' check, and reslaved as part of the 'after-take off/go-around checks'. Sitting on a heli-deck, you would sometimes notice a discrepancy between the E2 and the HSI, this could be up to 40 to 50 degrees.:uhoh:

[HughMartin]

The North Sea practice is to put the compasses to DG during before landing checks and then slave them after take off. For intensive shuttle flights, I would leave them on DG and maybe every 3rd of 4th take off re-slave them. IME most offshore installations will upset compasses by a good 30 or 40 degrees.

[ShyTorque]

Some years ago, I experienced a situation where we had to land on a rig to refuel, both outbound and inbound during a long range SAR. On the way out the compasses weren't affected. However, after refuelling a second time on the way back we departed with all three compasses reading differently. Until then, we had nothing in our SOPs to remind us to go to DG mode, but we did shortly after our return!

It did prove the benefit of carrying out gross error / compass checks though ;)

[bockywocky]

I have been flying quite a lot from ships and oil rigs (mostly for SAR) in the Navy. We use the good old Lynx that also has a GM9 gyrocompass with both slaved and DG modes.

For any normal operation we leave the compass in slaved mode and make sure after take-off from a ship or rig that you (or the PNF) slaves the compass and checks it with the standby compass.

Only if the gyro compass has a problem, or if you are operating at for instance 75 deg north, we switch it to DG.

[Avnx EO]

Great answers! ... Looks like once the compass has been in the disturbance long enough and has been pulled out of whack, it takes a fair amount of time to recover. What are we talking about here? 5 minutes? ten minutes? longer?

Avnx EO

[bockywocky]

Avnx EO,

I do not know all the compass systems, but the GM9 in our Lynx helicopter has a socalled "fast slave" button.

Slaving the compass with this fast slave mode uses a speed of 30 deg/sec so it takes maximum 6 seconds...

Indeed if you have to wait for the slaving in the normal compass mode it would take much longer (i do not remember by heart, but i think it was about 1 deg/sec).

[Gomer Pylot]

How long it takes depends on how far it's off, and on the DG installation. In general, a couple of minutes is about as long as it takes, sometimes less. In a B412, you can manually swing the heading indicator and put it back right, in the S76 you just throw a switch and let it right itself. I've never timed it exactly, but 1 or 2 minutes is about as long as I recall.

How long it takes depends on how far it\'s off, and on the DG installation. In general, a couple of minutes is about as long as it takes, sometimes less. In a B412, you can manually swing the heading indicator and put it back right, in the S76 you just throw a switch and let it right itself. I\'ve never timed it exactly, but 1 or 2 minutes is about as long as I recall. But 2 minutes can seem like an eternity under some conditions. :ooh:

[Flying Lawyer]

CAA Paper 2004/03 Helicopter Turbulence Criteria for Operations to Offshore Platforms

Safety Regulation Group
22 September 2004

SRG says:
The research reported in this paper was funded by the Safety Regulation Group of the UK CAA, and was performed by BMT Fluid Mechanics Limited, QinetiQ (Bedford) and Glasgow Caledonian University. The work was commissioned in response to a recommendation (10.2 (i)) that resulted from earlier research
into offshore helideck environmental issues, reported in CAA Paper 99004.
Turbulence around offshore platforms can represent a significant safety hazard and source of high cockpit workload. This was illustrated in the results of a questionnaire survey of offshore helicopter pilots, reported in CAA Paper 97009, where turbulence around platforms was ranked as the greatest of the fifteen factors contributing to workload and safety hazards that were considered.
Although the existing vertical wind speed criterion in CAP 437 in combination with a system of operational feedback (turbulence report forms) has served to contain the situation, the addition of a specific turbulence criterion which is calibrated to maximum safe pilot workload is viewed as a significant enhancement.
Work on validating the turbulence criterion using data from Bristow Helicopter’s helicopter operations monitoring programme (HOMP) is already underway. Once satisfactorily completed, the turbulence criterion will be added to CAP 437 and incorporated in the Offshore Helideck Design Guidelines document which the HSE commissioned with the support of the CAA, and is endorsed by the Offshore Industry Advisory Committee's Helicopter Liaison
Group (OIAC HLG).
A useful spin-off from the validation exercise will be the addition of an offshore helideck turbulence mapping capability to HOMP. This will enable helicopter operators with HOMP to better establish operating restrictions, and to monitor the turbulence environment around offshore platforms on a continuous basis with minimal effort. With this facility in place, any unannounced modifications to platform topsides adversely affecting the airflow over and around the helideck should be rapidly detected and appropriate changes to operating restrictions made.


Recommendations
Based on the conclusions of this report the following recommendations are made:

1 Use the criterion that the standard deviation of vertical velocity must not exceed 2.4 m/s as a working limiting turbulence criterion subject to further validation (subsection 9.1).

2 Reanalyse the predictors used to estimate HQR from pilot control activity using all the data available from the BRAE02 trial in order to derive coefficients of improved reliability for future general use (sub-section 4.6.8).

3 Seek validation of the entire modelling process and the limiting turbulence criterion against operational experience by means of:
a) Analysis of existing wind tunnel data using the new turbulence and existing vertical wind speed component criteria to predict the safe flight envelope for a number of offshore installations.
Compare the results with the Installation/Vessel Limitation
List (IVLL) for the installations concerned (sub-sections 8.6.1 and 9.1.2).
b) Implement the optimised HQR predictors (see recommendation 2 above) in the Helicopter Operations Monitoring Programme (HOMP) analysis, apply the analysis to the HOMP data archive and compare the resulting turbulence mapped around offshore installations with turbulent sectors as derived in a) above (subsections 8.6.2 and 9.1.2).
c) Use the analysis performed in b) above to identify specific severe turbulence events in the HOMP data archive, establish the turbulence levels likely to have been experienced from the associated wind conditions and wind tunnel data for the platforms concerned, and correlate this with the workload values obtained from the HOMP analysis (sub-sections 8.6.2 and 9.1.2).

4 Investigate the operational experience regarding the perceived increase in workload due to degraded visual conditions, and consider conducting further simulator trials to capture equivalent flight in turbulence data at night and in degraded meteorological conditions (sub-sections 4.6.7 and 9.1.2).

5 In the longer term, use data collected from the full-scale implementation of HOMP and optimised HQR predictors (see recommendation 2 above) to routinely map HQR around offshore installations, and make this information available to BHAB Helidecks to help improve and maintain the quality of the IVLL (sub-section 4.6.11).

6 Use data collected from the full-scale implementation of HOMP and optimised HQR predictors (see recommendation 2 above) to obtain evidence of any variation of turbulence induced pilot workload in different helicopter types. If it is apparent that significant differences are experienced across the offshore helicopter types in the fleet, consider extending the desktop simulation study to encompass selected types identified as particularly good or bad in this context (sub-section 5.2).

7 Consider re-assessing the 0.9 m/s vertical wind speed component criterion in the light of the new turbulence criterion (as proposed by [1]). However, note that this will require an improvement to the level of fidelity of the SyCoS model by implementing recent enhancements to produce more authentic control responses and consequently the ability to recognise and respect torque and power limits.




It's a big file (8.6mb). Dial-up users may wish to 'right-click' the link and select 'save target as...' to save the file.

Click: CAA Paper 2004/03 (http://www.caa.co.uk/docs/33/2004_03.pdf)

[CRAN]

Stephen Rowe, the managing director of BMT Fluid Mechanics presented a paper based on this work at last weeks European Rotorcraft Forum in Marseille. This is a much smaller piece of bedtime reading - approx 15 pages.

PM me if anyone wants a copy in pdf format.

CRAN

[pitchlink]

What on earth will the CAA think of wasting our money on next? The main comments I hear from around the crewroom is that there has never been any confusion in this regard betwen deck crews and aircraft crews, so why fix something that does not appear to be broken in the first place??!!!!!!!!

[Shawn Coyle]

I'd be concerned if I were a UK operator going to helidecks about this. (all of my following comments are based on not having read the document, so take them with a large grain of salt)
While it is useful in an academic sense, what possible use is it going to be in an operational sense?
How are we going to measure turbulence and then quantify it? If we can quantify it, can we then predict it in a manner that would be useful to the operator - it's a bit too late to have the turbulence reported to the pilot on short final where the decision might be 'Do I continue with the prospect that if anything happens I could be blamed for continuing in the knowledge of the turbulence level when my considerable experience tells me that this is OK?'

[212man]

I think the aim is to be able to derive scientifically derived, as opposed to emperical, limitations on Ops, when turbulence is predicted to reach certain levels. At present the limits in the HLL are best guestimates based on experience but do not have any basis in fact.

In a similar vein, the whole concept of pitch, roll and heave limits is being re-evaluated to come up with something based on facts and not incorrect assumptions.

[NickLappos]

Three comments:

1) What has happened that marks this need? remember the thread on "hard Cat A" where the prayer I have is that we first fix what is broken, then move to the fun and pleasure of fixing what is not.

2) What would we do with the data? Who knows what a helicopter can stand in upgust and side gust at low speed? What new tests will be cooked up, and will they bear any resemblence to the operating environment being questioned?

3) Will the regulators in their zest to make a new, shinier rule, make all helicopters the same by simply using the lowest common denominator when they set the rule? Will they ignore the very high pitch, roll and yaw control power of some machines, and restrict operations for all based on the assumed properties of the poorest helos?

[212man]

I don't think anyone is saying that "anything is broken".

Historically, platform/rig designers tended to site helidecks on the structure as an after thought, and were more concerned with the functionality of the 'rig' for its purpose than how the helideck location would be affected by its environment. So, traditionally, the hapless helicopter pilot turned up and dealt with the conditions as best he could. Sometimes they will be benign and landing is a simple task to accomplish, other times it will be downright frightening, and quite likely dangerous leaving the crew sighing a breath of relief when on the deck or possibly having to go around.

So to recognise this fact of life, the operators created restrictions, based on wind sector and strength, for those rigs with known problems (doesn't take too many approaches to the Brae with a 50 kt wind from the NW to realise that it's not big and it's not clever to keep doing it!)

Those limits were based on what 'felt right' for a particular type based on qualatative assessment by experienced pilots, such as the company test pilots, and would take the form of weight penalties that became progressively harsher as wind strength increased and normally reaching a limiting wind speed when ops would be banned.

Do these limits work? Well, up to a point they must do. Are the crew being put under an excessive workload such that they will lack spare capacity to deal with subsequent problems? Who knows; no-one calculated it, but probably in some cases. Are the passengers being exposed to a risk they should not be? Ditto.

With modern computing capabilities and simulation techniques, it would seem entirely sensible to look at this problem more carefully, surely? For any given platform design, a set of restricted crieria could be drawn up which would vary from type to type, based on their individual control and performance characteristics.

In what way can this be construed as a bad thing?

Do we really advocate the phillosophy of "off you go Bloggs to the XYZ rig which has a 60 kt wind, clad derricks and turbine exhaust plumes, and have a go, see how it feels and if you don't like it come back"?

Do we expect our B777 pilot taking us on holiday to 'shoot an approach' in a gusting 40 kt crosswind to see if "he can manage it"? I hope not; we expect him to say "no that's out of limits.

Where's the difference?

As I say, exactly the same principle applies to Pitch, Roll and Heave limits; some sort of limits had to be set originally, but with time it is obvious they are deficient in their logic. 3 degrees of roll for a deck 30 ft ASL is going to generate totally different accelerations and lateral displacements than one that is 130 ft ASL. Therefore an alternative is being sought.

I don't think the terms "zest", "cooked up" or "lowest common denominator" really apply in this context.

[JimL]

A couple of things that I would add to 212man's defense of this research and graphic description of flying to rigs in turbulent conditions: This research was undertaken as a result of an accident to an S61 in conditions under which it should not have occurred;

the first target of the research is the rig design process;

the wind tunnel data that is produced when the rig is designed and tested has never been used to provide data for an initial HLL (IVLL);

the HOMP system contains the weather data (produced from another system and inverted into the data set), the control movements, and the ability to analyse the pilot workload. At the moment pilot workload is assessed using a local algorithm produced by the (very able) HOMP manager. In the near future it will be replaced by a more specific algorithm that has been produced using Cooper Harper ratings.This system does exactly what Nick and Shawn were asking for some months ago when we were discussing the collection of data on the S92. It uses data, collected on line flights, to improve our knowledge of operations by assessing the the effect on handling of the turbulence environment of any rig and using it for statistical analysis.

This, my friends, is progress and not to be scoffed at.

[Shawn Coyle]

Don't get me wrong - I'm all for having better data to make decisions with. But the data has to be good, relevant data. My concern is that any data taken will not be as complete as it should be, that it may eventuallly be interpretted incorrectly, and we'll end up with restrictions and limitations that will negatively impact the industry.

Is this data taking going to include comprehensive information on the wind, gusts, vertical and lateral turbulence, aircraft motion, AFCS actuator operation, visual cues, and so on? Who is going to interpret it?
I know of an accident on a rooftop helipad where the helicopter should not have been operating in very gusty winds. There did not appear to be any consideration of the operating environment when the helipad was 'approved'. The question of the competence (read training and understanding of what was being approved) of the approver was never answered that I know of, nor whether winds or turbulence were ever addressed.
Ship operating limitations would be a good place to start looking at this (the problem obviously is that it's hard to drive an oil rig to generate the necessary wind envelopes...)

[RMAN]

Like NickLappos, I too have a prayer and that is that folk would read reports properly before passing comment.

As JimL has already helpfully pointed out, the turbulence criterion is for use during the initial rig design or modification process (along with the other criteria contained in CAP 437) and should help to create rigs that are more helicopter friendly and improve the information that goes into the HLL.

The control movement based pilot workload algorithms are being implemented in HOMP primarily to validate the maximum turbulence level produced by the research prior to inclusion in CAP 437. A secondary benefit will be to susequently use HOMP to establish polar plots a bit like SHOLs (workload level as a function of wind speed and direction - see Figures 7.4 and 7.6 in CAA Paper 2002/02 which are based on an 'informal' turbulence algorithm) for all rigs, and also permit continuous monitoring for unannounced changes to topsides (e.g. cladding of derriks, use of air gap for storage). This will support the existing turbulence report form process by automatically (via the HOMP ground station) providing consistent and objective data on the wind environment around all rigs.

[Ginger Spinner]

Any chance of starting a Test Pilot / thinks he's a Test Pilot page.

At least then you can wow each other with ever more ludicrous acronyms without boring the c**p out of those of us who commit that most heinous of crimes, "pitching up, deciding we don't like it and going home again"

[HughMartin]

Turbulence on offshore platforms has been a subject which has been doing the rounds since I was very wet behind the ears (and I am still drying out). Over the years we, on the UK sector of the North Sea, have produced a set of operational procedures and limitations which are used by all three operators called the Helideck Limitations List (HLL).

Turbulence by its very nature is chaotic and I don't believe we will be able to come up with a significantly better solution. Most newer helidecks have much less turbulence than the first generations ones which had no thought put into this problem. Modern ones usually have the helidecks on the west or south west corner so that the prevailing wind gives a clean airflow. Slab effect has also been reduced by providing large spaces between the helideck and the structures below it. No platform will be turbulence free in all wind conditions.

There are two issues from a practical point of view.

The first is to ensure the pilot is not put into a dangerous situation from which he/she will have a poor chance of recovering. At best, this might result in an overtorque or heavy landing which may require some sort of engineering inspection. The worst may include an inadvertent contact of inappropriate parts of the helicopter and the offshore installation resulting in a catastrophic event.

The second requirement is maintaining a standard of operational consistency to ensure we are all singing from the same hymn sheet. The customer and the pilots have some comfort in having a set of operational limitations which, by no means being scientifically derived, are the result of operational experience which usually errs on the safe side. This means we have the ability to predict the likelyhood of the job getting done or being postponed without having to think about whether pilot A or B is braver or better than pilot C or D. This helps eliminate commercial or peer pressure to get the job done when common sense should say "let's wait for a better time".

It is usually fairly obvious when turbulence is likely to exist by looking for the likely sources. A helideck in the lee of large exhaust pipes and/or obstructions should always be treated cautiously even in light wind conditions. Many of us are taught to fly an approach which is designed primarily to minimise the risk in the event of an engine malfunction i.e, keep translational lift as long as possible which will create a low power approach with a highish rate of descent. In the event of turbulence, this will usually require large power inputs to arrest the helicopter's inertia as it approaches the deck. I would suggest that the chance of engine malfunction during approach is very remote. If turbulence is likely, you are going to be in a much better position if your final approach to the deck is made at a slow forward speed and a slow rate of descent. This means having power applied early so that there is no need for large changes of power close to the hard objects.

It is also a good idea to brief your passengers before the approach that it is likely to be bumpy. This usually causes all turbulence to disappear and the passengers left wondering what the heck you were talking about. But I would rather have that than having to fill in all the paperwork following a heavy landing or overtorque.

[Hummingfrog]

What do the offshore pilots think of the new terminology of "Deck availabe for landing" replacing "Deck is clear for landing".

My thoughts are it is replacing a clear concise reply with waffle. By all means change the previous "negative deck clear" with "deck unavailable" to avoid confusion.

I must admit in 15+yrs on the N Sea I have never heard "negative deck clear" it has always been "standby" while the deck crew assembled or no reply because nobody had told the deck crew your ETA!!!

This is a change to address a perceived problem that doesn,t exist

HF

[cpt]

What about " Green helideck " or " Red helideck " ?
The HLO, not beeing a qualified ATC controller is in principle not authorized to give a proper landing clearance.

[Delta Julliet Golf]

Well, always better than : "Land at your own discretion"

or

"DECKCLEARFORLANDINGCREWSTANDINGBY!" in speed language with 5 other aircraft asking for their deck clearances ;)

DJG

[332mistress]

I agree with Hummingfrog. Who thought this up. It is obviously nobody who flies offshore. Why use a 4 syllable word when a one syllable word was more than adequate.

I thought that it was sensible not to use the same word in the question as the answer. We do not now call "ready for take off" but "ready for departure" at an airfield to stop someone thinking that a call for "take off" was their permission to take off.

Most off the N sea is divided into sectors with each rig in that sector on the same frequency. It is not unusual for 2 helicopters to be making their approaches to different rigs at the same time on the same frequency.

It will be possible for one helicopter to mistake the others request " Is the DECK AVAILABLE FOR LANDING" for the answer "affirm DECK AVAILABLE FOR LANDING":uhoh:

Lets go for Hummingfrog's suggestion of "Deck clear" and "deck unavailable" two distinct phrases


332M

[Deck Clear]

This has irritated me no end . Its another imposed decision from on High....made without consultation of the people who fly in the North Sea. If it's not broke.......WHY? During shuttles there are often other aircraft in the same field on the the same freq. Short, sharp calls are the norm....not this long winded waffle!
We often do 25+ sectors in a day.
Another example of the "we know best" school of legislation.:mad:

[Moochie Moo]

JimL, I read your other post regarding the HOMP report with interest and wanted to express my views:

HOMP is the latest version of the North Sea's 'Emperor's New Clothes'.

If you think an algorithm based on Cooper-Harper ratings can assess workload without the qualitative input of a calibrated human, it goes to show how little is understood about what is being done here. Give industry a fraction of what is being spent on this white elephant in the form of additional training hours and efforts training-the-trainer, and I assure you the rate of incidents will reduce.

This is another example of what the UK 'committee syndrome' spawns, regurgitating the same issues year after year achieving very little in real-world operational safety matters and when money is spent, it is misdirected.

Rig design for helicopter operations is not rocket science, and neither is landing a helicopter on a rig. Developing HOMP for turbulence assessment is nothing more than idle intellectual musings.

If HOMP has been recommended for inclusion in ICAO Annex 6 Part III (tell me it ain't so!), my bet is was done so by someone who knows little of operating outside of the North Sea. To put this forward for inclusion in an international document is waaaay too premature.

It isn't progress JimL, it's misidentification of the real issues. This whole subject is also a case-in-point of why the Americans have a helicopter manufacturing industry and the British don't.

Disregard the last sentence. I had the urge to finish on an inflammatory note.

[JimL]

MM:

I am astounded at the breadth of your knowledge but cannot fault your comment on training - I take it that you have not read any of these reports?

[flyer43]

Here's a question for all you budding theorists out there.
Looking at offshore operations to raised helidecks - can anybody provide me with a "simple" calculation to illustrate the variation in ground cushion effect with the reduction in helideck size? eg. starting off with a helideck size of 1.5D and reducing down to 0.75D or less.
Thanks in advance for any contributions and Seasons Greetings to one and all

[Giovanni Cento Nove]

If you mean by operations then assuming it's commercial how small do you want to go and still remain legal and also be covered by insurance?

If it's a Cat A operation it will tell you the size in the RFM for each type and the deck may end up being bigger than 1.5D.

More details would help.

[flyer43]

It's not so much a question of legality - this is purely a question about helicopter aerodynamics. Maybe if I asked the question in a different way - Is there a simple way of expressing the reduction in ground cushion effect between a helicopter sitting nicely in the middle of a large helideck compared to one which is hovering with an increasing amount of rotor disc extending beyond the helideck edge. i.e. What is the difference in power required to maintain the same hover height with respect to the helideck?

[bugdevheli]

Rotor dia say 30 feet Diameter of pad (assuming round pad) say 30 feet. power required to hover at 15 feet is approx two thirds of that to hover out of ground effect. On the basis that only the outer half of your blades are producing significant lift, any reduction in the size of the pad from that of your rotor diameter will greatly reduce your lift and increase your induced power requirement. Look at it this way. If your rotor span is 30 feet and your pad is 25feet, at a 15 foot hover directly over the pad you now have the outer two feet six inches of each blade that are no longer in ground effect but are obviously providing the same lift as they do out of ground effect therefore when I am sober and not rambling on like a pratt I will produce a graph which you can pin on your windscreen which can be refered to whilst executing a 30feet dia helipad landing. You will need to carry out some mathematical work to evaluate the graph , this is best done by holding a 30inch pencil bitween ones teeth to allow unimpeded access to the graph stuck on the screen . Wishing you a happy and safe Christmas Bug.

[NickLappos]

Nice question!

The max ground effect is about 20% (you reduce power by about 20% when in very low IGE vice OGE). For smaller decks, where the rotor is not fully IGE, the effect is rapidly reduced, I'll bet, but I have no data. If one is squarely over a 1D pad, the effect should be just about 100%, since the rotor wake contracts to a tighter diameter than the rotor.

As rotordevheli says, the max velocities are at the tips, so one would believe a half Diameter pad would produce very much less than half the IGE recovery (also, the area of a half diameter pad is only 25% of the total disk.)

I doubt that anyone has actually measured the effect, though.

[goaround7]

It' s not very scientific but I've had students land on a narrow bank with steep drop off fore and aft. Naturally they are more worried about falling off the bank but it's interesting to note that the power requirement in a piston Enstrom is only about one to one and a half inches less MP than for OGE so it obviously affects greatly.

There is no noticeable pitch effect so I presume the (90 degree precessed) increased lift from the left and right sections of the disc cancel out.

Will a similar cancellation occur on a small square pad ? I supposed proximity to superstructure and wind will affect greatly also ?

[Hilico]

No-one's actually measured this?!?! Come on, let's get out there and measure!! I would volunteer to do the flying, but my stationery hover takes in about 5D.

[212man]

Working on a formula: how keen is that (who said sad?????)

Happy Christmas

[flyer43]

Thanks for the feedback so far. I know the practical answer to my question having spent many years flying to offshore installations and several years as a flying instructor at a cpl(h) school where sloping ground landings with students certainly made you more than aware of the difference in power requirements from working with a flat surface - albeit a much larger one than the average offshore platform.

If anybody is actually sad enough to work out even a very basic formula in response to my original question I would be very interested and very grateful.

BUG - I hope that your hangover is cured by now, although the big New Year one is imminent!! When you eventually recover next year I'd be interested in the graphs you were talking about - might be difficult to make the measurements with a pencil between my teeth while holding a stable hover over a moving helideck though....

Wishing you all the very best for 2005

[Geoffersincornwall]

Have noticed that with something like a 61 that just to confound your best estimates at performance on the offshore deck (twin engine HOGE weight) there are times when at zero wind you just can't make it. Reckon this is because some of the surrounding vertical structures are contributing a bit of recirculation on part of the disc. There were certainly many occasions in the (bad) old days when you just air taxied off the deck and converted height to speed. Anybody have similar experiences?

[NickLappos]

Geoffersincornwall,

To understand your observation more clearly, can you tell us what you "just can't make" Is it an OGE hover, towering takeoff, or something else?
Thanks,
N

[The Rotordog]

This is totally anecdotal and probably worthless, but it made me scratch my head a bit. The popular theories may be wrong.

A long time ago when I first started flying offshore (GOM), I wondered about this very thing, i.e. how much ground cushion does the platform provide? I was flying a 206B while based on a tall, three-story, slab-sided quarters building that measured 50'X70'. The entire roof was the helideck, and the surrounding fence was bare chain link and therefore of no ground-cushion value.

In an experimental mood (and being dumber than a box of rocks), I decided to see if I could measure any torque difference or cyclic displacement change with the helicopter hovering half-on and half-off the deck. I chose a calm summer day - not hard to do.

With just me in the ship and with the disk dead-center over the deck, I was hovering right around 72%Q. I moved over to the edge and positioned the B-model exactly half-on/half-off. To my surprise, the torque stayed right at 72%. The cyclic *seemed* to be in the same place as far as I could tell (but then I couldn't accurately measure it). Puzzled, I moved back over the pad: 72%. Back to the half-off position: 72%.

Nervous as I was, flirting with disaster like that I did not experiment by moving too much further outward to see where the transition from IGE to OGE was noticed. In retrospect, I wish that I had quantified it, but my uniform shirt at the time did not have a nametag that said "N. Lappos." And I was afraid one of our "big ships" would be flying over with the guys looking down and going, "What the hell is that B-model doing hovering half-off the deck? Get the Chief Pilot on the phone!"

I was pretty confused, but what this seemed to tell me was that the effects of the ground cushion on takeoff probably extended out at least half-a-disk or so (genius!). Conversely, the same probably held true for landing, although I confess that this is an assumption (with all that entails).

Shortly afterward, I moved on to bigger aircraft and other (smaller) platforms, my "playing around" decreased and I stopped asking myself questions like, "What happens if you hover half-on and half-off a platform?"

[Peter PanPan]

Great story Rotordog, why isn´t anyone posting on this thread anymore?

[Bravo73]

Great story Rotordog, why isn´t anyone posting on this thread anymore?

Because it's over 6 years old... :rolleyes:

[Peter PanPan]

Bravo73 seems like you just lost an opportunity to remain quiet.

I did notice that it´s been 6 years since the last post, Helideck Ops continue to be a relevant topic though, at least for anyone flying Offshore.

[Bravo73]

If you ask an obvious question, you'll get an obvious answer. :E

But although you seem to like resurrecting things from dead, there have been plenty of other threads in the last 6 years which have discussed offshore landings. I imagine that the various participants were happy with those threads.

[Peter PanPan]

Certainly do enjoy resurrecting "quality threads" on interesting topics, that is exactly why I keep perusing those 6 years discussions and perhaps newer members may have something to share on that as well :ok: