10.0 HELIDECK ENVIRONMENTAL EFFECTS
10.1 INTRODUCTION
The safety of offshore helicopter flight operations can be seriously affected by environmental effects that may be present around installations, vessels and their helidecks. These environmental effects are typified by structural turbulence, the thermal effects caused by gas turbine and diesel exhaust emissions, hot and cold gas streams and vessel motions.
It is vital, in order to ensure the safety of helicopters operating to and from offshore installations and vessels, that the best possible flying environment (minimum turbulence and helideck movement) is maintained.
Where, for operational and/or meteorological reasons, ideal flying conditions do not prevail, then flight crews need to have access to as much information as possible on the anticipated turbulent conditions and helideck movements in order to plan or abort flight operations.
This section addresses, in detail, the environmental effects likely to be encountered, and provides information on how to identify problems during the design process and ways that these adverse effects can be mitigated.
10.2 MAIN REFERENCES
CAP 437, Chapter 3.
CAA Paper 99004 - Research on Offshore Helideck Environmental Issues
[Ref: 41].
BMT Report - Helideck Design Considerations Environmental Effects [Ref: 68].
10.3 BACKGROUND
It is almost inevitable that helidecks installed on the cramped decks of offshore structures will suffer to some degree from their proximity to tall and bulky structures, and to gas turbine exhausts and flares. The objective of this section is to help platform designers to create offshore installation topsides designs, and helideck locations, that are safe and ‘friendly’ to helicopter operations and, as far as possible, avoid the ‘environmental’ effects (mainly aerodynamic, thermal and wave motion) which can affect helicopter operations. It is hoped that, if used from ‘day one’ of the offshore installation design process when facilities are first being laid out, this section will prevent or minimise many helideck environment problems at little or no cost to design or construction.
Guidance on the design and placement of offshore helidecks has existed for many years in the CAA document CAP 437 [Ref: 40], which contains certain environmental criteria relating to the occurrence of downdraft and higher than ambient temperatures due to exhausts and flares. These criteria were set in order to ensure safe helicopter operations by avoiding these hazards. Where these criteria could not be met, or where pilots experienced other environmental phenomena, an entry has been placed in the Helideck Limitation List (HLL) (previously known as the Installation / vessel Limitation List - IVLL). These entries are specific to particular combinations of wind speed and direction, and either restrict helicopter weight, or prevent flying altogether in certain weather conditions.
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