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.
Last edited by HughMartin; 9th Oct 2004 at 05:06.