Offshore Helideck Design Guidelines

 

Helideck

This article provide general guidelines for layout of Helideck on offshore platforms. It is important that the local aviation regulations are adhered to in all cases. Helideck design shall take into consideration the following items, as a minimum:

• Size and structural adequacy for selected helicopter
• Orientation with respect to prevailing winds
• Gas / exhaust emissions and turbulence environment
• Effects of vessel motions
• Suitable helideck height
• Clear landing approach and take-off paths
• Obstructions within permitted limits
• Falling gradient of 5:1
• Access and escape routes
• Parking arrangements, if provided
• Lighting
• Markings
• Friction surface
• Tiedowns
• Helideck net and perimeter safety net
• Refuelling facilities
• Firefighting equipment

The helideck should be located on the highest level of the platform to ensure that the helicopter approaching and departing the platform is free from any obstructions due to cranes, turbine exhausts, flare booms or any other tall structures.

Size of Helideck

For design purposes, the dimensions of the helicopter are critical for sizing the helidecks, while the maximum gross weight of the helicopter is critical in terms of the structural loads to be borne by the supporting helideck structure. The key characteristic used to size the helideck for design purposes is the “D Value” for the critical helicopter. This dimension reflects the maximum overall dimension of the critical helicopter when its rotors are turning. For a single rotor helicopter this means the length of the aircraft from the extremity of the rotor circle at the front of the helicopter to the extremity of the tail rotor at the rear of the helicopter. For example, the D value for Bell 212 helicopter is 17.46m and D value for AW 139 helicopter is 16.66m.

Orientation with respect to prevailing winds

The prevailing wind direction in the vicinity of the proposed helideck will dictate the direction of flight operations for helicopters landing or taking off from the proposed offshore structure. In the critical phases of touching down on, or lifting off, a helideck it is most important that helicopters are aligned into wind, since at these times these aircraft are susceptible to the effects of crosswinds.

All attempts should therefore be made to ensure that the approach and takeoff orientations are aligned as close as possible into the prevailing winds.

Exhaust emissions and turbulence environment

Offshore installations topsides tend to include a number of tall structures such as drilling derricks, flare towers, cranes, gas turbine exhaust stacks etc. Usually it is impractical to locate the helideck at a higher elevation. All such tall structures will cause areas of turbulence that may potentially pose a hazard to the helicopter. It should be noted that the location and configuration of drilling derricks can vary during the life of the field. The assessment of the helideck location should take into account the various derrick configurations that are expected to occur during the life of the installation.

Obstacle Free Sector

A minimum 210° obstacle free sector is required. Its point of origin on the inboard side of the deck is the apex of the chevron marked on the helideck. By extending a line out from each leg of the chevron, a check is required to ensure freedom from obstructions within the 210° sector by identifying items that are above deck level. Such items may not exceed 250 mm in height, and even then must be restricted to specified essentials such as lighting fittings, safety net rails, etc. as specified in CAP 437. Helidecks are normally located on the platform corners remote from the other facilities in order to comply with 210° obstruction-free sector, and for best aerodynamic performance.

Falling Gradient

The falling gradient sector comprises a 180° arc that falls within the 210° Obstacle Free Sector , and extends downward from the edge of the safety net of the helideck towards the water line at a slope of 5:1. Helideck should be provided with an unobstructed 5:1 falling gradient below the landing area. This unobstructed space permits the helicopter to descend safely after take off in the event of engine failure, so as to "fly away" climbing speed.

Access and escape routes

The personnel access and egress points must be optimally located in terms of their alignment relative to the helicopter parking position. The personnel access and egress points for the helideck must be situated in a position so that access can be gained to the helicopter without interference with the helicopter’s tail rotor. Similarly the passengers leaving the helicopter should not be exposed to the tail rotor. In other words, the access and egress points must be located away from the rotating tail rotor of a parked helicopter. The design should ensure that the egress from the helideck under emergency situations can be made in the safest possible manner.

Helideck Markings

Markings provide critical information to flight crews when approaching, operating on, and departing from a helideck. They are an essential safety feature for the operation of aircraft using the helideck and are required under the ICAO Annex 14 standards. Particular markings that must be provided on a helideck are:

• A large “H” marking, placed in the centre of the helideck, oriented in the direction of the flight approach, conforming to a specified size and dimensions
• A Touchdown/Position Marking surrounding the “H”
• An Obstacle Free Area Marking denoting the origin and direction of the Obstacle Free Surface
• A Helideck Perimeter marking
• The Helideck D-Value
• The Helideck Name
• The T-Value of the heaviest helicopter for which the helideck is designed to accommodate

Rescue and Fire Fighting Services

The purpose of having a fire-fighting capability on a helideck is not to safeguard those who may be present on the structure at any time, but to provide an ability to suppress a fire on a helicopter that may be on fire when landing on the helideck, or catches fire after landing. The essential purpose of helideck fire suppression is therefore related to the operation of the helicopter, and the need to suppress or extinguish a helicopter fire, especially a fuel fire, and to enable occupants of the helicopter to escape from a burning aircraft. As far as the Rescue & Fire-fighting requirements for helidecks is concerned, ICAO Annex 14 Volume II establishes that the fire-fighting requirements specified for helidecks in the ICAO Heliport Manual should be met. This defines the required helideck fire-fighting capabilities to comprise those required under the “Code for the Construction and Equipment of Mobile Offshore Drilling Units” published by the International Maritime Organisation (IMO). The IMO requirements specify that helidecks should be equipped with the following:

• At least 2 dry powder extinguishers having a total capacity of not less than 45kg
• A suitable foam application system consisting of monitors or foam-making branch pipes capable of delivering foam solution to all parts of the helicopter deck at a rate of not less than 6 L/min for at least 5 min for each square metre of the area contained with a circle of diameter “D”
• Carbon dioxide extinguishers of a total capacity of not less than 18kg or equivalent
• At least two dual purpose nozzles and hoses sufficient to reach any part of the helicopter deck

The above are the current requirements for helideck fire-fighting capability, which are not mandatory as far as ICAO is concerned, although it is noted by ICAO that these requirements ‘should’ be met.

Source: Piping World