What is Helideck
A Helideck is a helicopter landing area on board a ship,offshore rig and floating platforms. Unlike surface helipads,helidecks are very complicated to design and fabricate.
Structural Design HeliDeck
The take-off and landing area should be designed for the heaviest and largest helicopter anticipated to use the facility. Helideck structures should be designed in accordance with relevant International Organization for Standardization (ISO) codes for offshore structures and for floating installations. The maximum size and mass of helicopters for which the helideck has been designed should be stated in the Installation/Vessel Operations Manual and Verification and/or Classification document. operational flexibility may be gained from considering the potential life and usage of the facility along with likely future developments in helicopter design and technology. Consideration should also be given in the design to other types of loading such as personnel, other traffic, snow and ice, freight, refuelling equipment, rotor downwash etc. as stated in the relevant ISO codes. It may be assumed that single main rotor helicopters will land on the wheel or wheels of two landing gear (or both skids if fitted). The resulting loads should be distributed between two main undercarriages. Where advantageous a tyre contact area may be assumed in accordance with the manufacturer’s specification. Ultimate limit state methods may be used for the design of the helideck structure, including girders, trusses, pillars, columns, plating and stiffeners.
A serviceability limit check should also be performed to confirm that the maximum deflection of the helideck under maximum load is within code limits. This check is intended to reduce the likelihood of the helideck structure being so damaged during an emergency incident as to prevent other helicopters from landing. Consideration should be given to the possibility of accommodating an unserviceable helicopter in a designated parking or run-off area (where provided) adjacent to the helideck to allow a relief helicopter to land. If this contingency is designed into the construction/operating philosophy of the installation, the helicopter operator should be advised of any weight restrictions imposed on the relief helicopter by structural integrity considerations.
Where a parking or run-off area is provided it is assumed that the structural considerations will at least meet the loads criteria applicable for helicopters at rest. The loads and load combinations to be considered should include: a) Dynamic load due to impact landing. This should cover both a heavy normal landing and an emergency landing. For the former, an impact load of 1.5 x MTOM of the helicopter should be used. After considering the design of the helideck structure’s supporting beams and columns and the characteristics of the designated helicopter, the dynamic load should be increased by a suitable structural response factor depending upon the natural frequency of the helideck structure. It is recommended that a structural response factor of 1.3 should be used unless further information allows a lower factor to be calculated. Information required to do this will include the natural periods of vibration of the helideck and the dynamic characteristics of the designated helicopter and its landing gear.
The helideck should be designed to withstand all the applied forces that could result from a helicopter at rest; the loads which should be taken into account: a) Imposed load from helicopter at rest. All areas of the helideck accessible to a helicopter, including any separate parking or run-off area, should be designed to resist an imposed load equal to the MTOM of the helicopter. This load should be distributed between all the landing gear. It should be applied in any position on the helideck so as to produce the most severe loading on each element considered. Overall superimposed load.
To allow for personnel, freight, refuelling equipment and other traffic, snow and ice, rotor downwash etc., an allowance of 2.0 kilo Newtons per square metre (kN/m2) should be added to the whole area of the helideck.
Size and Obstacle Protected Surfaces.
The location of a specific helideck is often a compromise given the competing requirements for space. Helidecks should be at or above the highest point of the main structure. This is a desirable feature but it should be appreciated that if this entails a landing area much in excess of 60 m above sea level, the regularity of helicopter operations may be adversely affected in low cloud base conditions. For any particular type of single main rotor helicopter, the helideck should be sufficiently large to contain a circle of diameter D equal to the largest dimension of the helicopter when the rotors are turning. This D-circle should be totally unobstructed .
Due to the actual shape of most offshore helidecks, the D-circle will be ‘hypothetical’ but the helideck shape should be capable of accommodating such a circle within its physical boundaries. From any point on the periphery of the above mentioned D-circle an obstacle-free approach and take-off sector should be provided which totally encompasses the landing area (and D-circle) and which extends over a sector of at least 210°. Within this sector,obstacle accountability should be considered out to a distance from the periphery of the landing area that will allow for an unobstructed departure path appropriate to the helicopter the helideck is intended to serve. Helicopters operated in Performance Class 1 or 2, the horizontal extent of this distance from the helideck will be based upon the one-engine inoperative capability of the helicopter type to be used. In consideration of the above, only the following items essential for safe helideck operations may exceed the height of the landing area, but should not do so by more than 25 centimetres for any helideck where the D-value is greater than 16.00 m or by more than 5 cm for any helideck where the D-value is 16.00 m or less: • the guttering,the lighting required, the foam monitors (where provided); and those handrails and other items (e.g. EXIT sign) associated with the landing with the landing area which are incapable of complete retraction or lowering for helicopter operations.
Objects whose function requires that they be located on the surface of the helideck such as landing nets, tie-down points, and “circle” and “H” lighting systems should not exceed a height of 25 mm. Such objects should only be present above the surface of the touchdown area provided they do not cause a hazard to helicopter operations. The bisector of the 210° Obstacle Free Sector (OFS) should normally pass through the centre of the D-circle. Acceptance of the ‘swung’ criteria will normally only be applicable to existing installations. No objects above 25 cm (or 5 cm where the D-value of the helideck is 16.00 m or less) are permitted in the first segment of the LOS. The first segment extends out to 0.62D from the centre of the D-circle, or 0.12D from the landing area perimeter marking. The second segment of the LOS, in which no obstacles are permitted to penetrate, is a rising 1:2 slope originating at a height of 0.05D above the helideck surface and extending out to 0.83D from the centre of the D-circle (i.e. a further 0.21D from the edge of the first segment of the LOS).
The landing area should have an overall coating of non-slip material and all markings on the surface of the landing area should be finished with the same non-slip materials. Whilst extruded section or grid construction aluminium (or other) decks may provide adequate resistance to sliding, they should be coated with a non-slip material unless adequate friction properties have been confirmed by measurement.. It is important that adequate friction exists in all directions and in worst case conditions, i.e. when the deck is wet. Over-painting friction surfaces on such designs with other than non-slip material will likely compromise the surface friction. Suitable surface friction material is available commercially Helidecks on fixed installations should be cambered (or laid to a fall) to approximately 1:100. Any distortion of the helideck surface on an installation due to, for example, loads from a helicopter at rest should not modify the landing area drainage system to the extent of allowing spilled fuel to remain on the deck. A system of guttering on a new-build or a slightly raised kerb should be provided around the perimeter to prevent spilled fuel from falling on to other parts of the installation and to conduct the spillage to an appropriate drainage system. The capacity of the drainage system should be sufficient to contain the maximum likely spillage of fuel on the helideck. The calculation of the amount of spillage to be contained should be based on an analysis of helicopter type, fuel capacity, typical fuel loads and uplifts. The design of the drainage system should preclude blockage by debris. The helideck area should be properly sealed so that spillage will only route into the drainage system.
Tautly-stretched rope netting should be provided to aid the landing of helicopters with wheeled undercarriages in adverse weather conditions. The intersections should be knotted or otherwise secured to prevent distortion of the mesh. It is preferable that the rope be constructed of sisal, with a maximum mesh size of 200 mm. The rope should be secured at intervals approximately 1.5 metres between the lashing points around the landing area perimeter and tensioned to at least 2225 N. Subject to acceptance by the agency responsible for the certification of the helideck, netting made of material other than sisal may be considered but netting should not be constructed of polypropylene-type material which is known to rapidly deteriorate and flake when exposed to weather. Tensioning to a specific value may be impractical offshore.
Sufficient flush fitting (when not in use) tie-down points should be provided for securing the maximum sized helicopter for which the helideck is designed. They should be so located and be of such strength and construction to secure the helicopter when subjected to weather conditions pertinent to the installation design considerations. They should also take into account, where significant, the inertial forces resulting from the movement of floating units. b, it should not be possible to raise any part of the net by more than approximately 250 mm above the helideck surface when applying a vigorous vertical pull by hand. The location of the net should ensure coverage of the Tie-down points should be compatible with the dimensions of tie-down strop attachments. Tie-down points and strops should be of such strength and construction so as to secure the helicopter when subjected to weather conditions pertinent to the installation design considerations. The maximum bar diameter of the tie-down point should be 22 mm in order to match the strop hook dimension of the tie-down strops carried in most UK offshore helicopters. Advice on recommended safe working load requirements for strop/ring arrangements for specific helicopter types can be obtained from the helicopter operator.
Safety nets for personnel protection should be installed around the landing area except where adequate structural protection against a fall exists. The netting used should be of a flexible nature, with the inboard edge fastened just below the edge of the helicopter landing deck. The net itself should extend at least 1.5 metres in the horizontal plane and be arranged so that the outboard edge does not exceed the level of the landing area and angled so that it has an upward and outward slope of approximately 10°.
A safety net designed to meet these criteria should ‘contain’ personnel falling into it and not act as a trampoline. Where lateral or longitudinal centre bars are provided to strengthen the net structure they should be arranged and constructed to avoid causing serious injury to persons falling on to them. The ideal design should produce a ‘hammock’ effect which should securely contain a body falling, rolling or jumping into it, without serious injury. When considering the securing of the net to the structure and the materials used, care should be taken that each segment will be fit for purpose.
For reasons of safety it is necessary to ensure that embarking and disembarking passengers are not required to pass around the helicopter tail rotor, or around the nose of helicopters having a low profile main rotor, when a ‘rotors-running turn-round’ is conducted (in accordance with normal offshore operating procedures). Many helicopters have passenger access on one side only and helicopter landing orientation in relation to landing area access points is therefore very important. 10.2 There should be a minimum of two access/egress routes to the helideck. The arrangements should be optimised to ensure that, in the event of an accident or incident on the helideck, personnel will be able to escape upwind of the landing area. Adequacy of the emergency escape arrangements from the helideck should be included in any evacuation, escape and rescue analysis for the installation, and may require a third escape route to be provided.
Where handrails associated with helideck access/escape points exceed the height limitations given they should be retractable, collapsible or removable. When retracted, collapsed or removed the rails should not impede access/egress. Handrails which are retractable, collapsible and removable should be painted in a contrasting colour scheme. Procedures should be in place to retract, collapse or remove them prior to helicopter arrival. Once the helicopter has landed, and the crew have indicated that passenger movement may commence, the handrails may be raised and locked in position.
The handrails should be retracted, collapsed or removed again prior to the helicopter taking off. NOTE: The helicopter crew will switch off the anti-collision lights to indicate that the movement of passengers and/or freight may take place (under the control of the HLO). Installation/vessel safety notices placed on approach to the helideck access should advise personnel not to approach the helicopter when the anti-collision lights are on. Visual Aids. The name of the installation should be clearly displayed in such positions on the installation so that it can be readily identified from the air and sea from all normal angles and directions of approach. For identification from the air, the helideck name and the side identification panels are used. It is not necessary, nor is it a legal requirement, to complicate recognition processes by inclusion of ‘block numbers’, company logos, or other designators. In fact, complication of identifiers can be confusing and will unnecessarily, and undesirably, extend the mental process of recognition at the critical time when the pilots’ concentration is being fully exercised by the demands of the landing manoeuvre. The names on both identification markings should be identical, simple and unique and facilitate unambiguous communication via radio. The approved radio callsign of the installation should be the same name as the helideck and side panel identifier. Where the inclusion of ‘block numbers’ on side identification panels is deemed to be essential (i.e. for purposes other than recognition), the name of the installation should also be included; e.g. ‘NAME. BLOCK NO.’ The installation identification panels should be highly visible in all light conditions. They should be suitably illuminated at night and in conditions of poor visibility. In order to minimise the possibility of ‘wrong rig landings’ use of new technology is encouraged so that identification can be confirmed in the early stages of the approach by day and night. Modern technology is capable of meeting this requirement in most ambient lighting conditions. Use of high-intensity Light Emitting Diode (LED) cluster or fibre-optic systems in other applications have been shown to be effective even in severely reduced visibility. Additionally, it is recognised that alternative technologies have been developed consisting of highly visible reflective side signage that has been successfully installed on some installations with the co-operation of the helicopter operator.
( Helideck markings (specifically the installation identification marking) and side identification panels are used by pilots to obtain a final pre-landing confirmation that the correct helideck is being approached. It is therefore VITAL that the helideck markings and side identification panels are maintained in the best possible condition, regularly re-painted and kept free of all visibility-reducing contaminants. Helideck owners/operators should ensure that specific inspection and re-painting maintenance procedures and schedules for helideck markings and side identification panels take account of the importance of their purpose. Side identification panels should be kept free of any obscuring paraphernalia (draped hoses etc.) and be as high as possible on the structure.
The installation identification should be marked on the helideck surface between the origin of the OFS and the TD/PM Circle in symbols not less than 1.2 metres high and in a colour (normally white) which contrasts with the helideck surface. The name should not be obscured by the deck net (where fitted). Helideck perimeter line marking and lighting serves to identify the limits of the Landing Area for day and night operations respectively.
A wind direction indicator (windsock) should be provided and Helideck Landing Area Markings. The colour of the helideck should be dark green. The perimeter of the landing area should be clearly marked with a white painted line 30 cm wide. Nonslip materials should be used. Aluminium helidecks are in use throughout the offshore industry. Some of these are a natural light grey colour and may present painting difficulties. The natural light grey colour of aluminium may be acceptable in specific helideck applications where these are agreed with the agency responsible for the certification of the helideck. This should be discussed in the early design phase. In such cases the conspicuity of the helideck markings may need to be enhanced by, for example, overlaying white markings on a painted black background. Additionally, conspicuity of the yellow TD/ PM Circle may be enhanced by outlining the deck marking with a thin black line located so as to indicate the free stream wind conditions at the installation/vessel location. It is often inappropriate to locate the primary windsock as close to the helideck as possible.