13.3 Construction
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Statutory Documents - IMO Publications and Documents - International Codes - 1989 MODU Code – Code for the Construction and Equipment of Mobile Offshore Drilling Units, 1989 – Resolution A.649(16) - Chapter 13 – Helicopter Facilities1 - 13.3 Construction

13.3 Construction

  13.3.1 The helideck should be of a design and construction, adequate for the intended service and for the appropriate prevailing climatic conditions, approved to the satisfaction of the Administration.

  13.3.2 For adverse climates as determined by the coastal State, taking into account the type of helicopter used, the conditions of wind, turbulence, sea state, water temperature and icing conditions, the helideck should meet the following requirements with reference to ICAO Annex 14 Volume II (Heliports):

  • .1 The helideck should be of sufficient size to contain an area within which can be drawn a circle of diameter not less than LD for single main rotor helicopters and not less than 0.9 LD for tandem main rotor helicopters.

  • .2 Where the provisions of 13.3.2.1 cannot be met for helicopters having tandem main rotors, the helideck may be in the form of a rectangle with a small side not less than 0.75 LD and a long side not less than 0.9 LD, but within this rectangle, bidirectional landings only should be permitted in the direction of the 0.9 LD dimension. Where necessary for design purposes, any corners of the rectangle may be omitted, provided that neither of the two sides forming the right angle of the omitted triangle exceed 5 m in length.

  • .3 The obstacle-free sector should be not less than 210°.

  • .4 For single main rotor and side by side twin main rotor helicopters, within the 150° limited obstacle sector out to a distance of 0.62 LD, measured from the centre of the helideck, objects should not exceed a height of 0.05 LD above the helideck. Beyond that arc, out to an overall distance of 0.83 LD, the limited obstacle sector rises at a rate of one unit vertically for each two units horizontally (see figure 13-1).

  • .5 For omnidirectional operations by tandem main rotor helicopters, within the 150° limited obstacle-free sector out to a distance of 0.62 LD, measured from the center of the helideck, no fixed obstacles should be allowed. Beyond that arc, out to an overall distance of 0.83 LD, the obstacle height is limited to 0.05 LD (see figure 13 -2 ) .

  • .6 For bidirectional operations by tandem main rotor helicopters, within the 0.62 LD arc in the 150° limited obstacle-free sector, objects should not penetrate a level surface which has a height equivalent to 1.1 m above the helideck (see figure 13-3).

  • .7 In the immediate vicinity of the helideck, over an area of at least 180° with the origin at the centre of the helideck, obstacles such as booms, derricks, sponsons, etc., should not protrude beyond a descending gradient having a ratio of one unit horizontal to five units vertically measured from the edge of the helideck downward.

Figure 13-1 Helideck obstacle limitation sector
Single main and side-by-side twin rotor helicopters in adverse climate

Figure 13-2 Helideck obstacle limitation sector
Tandem main rotor helicopters – Omnidirectional operations in adverse climate

Figure 13-3 Helideck obstacle limitation sector
Tandem main rotor helicopters, bidirectional operations in adverse climate

  13.3.3 For moderate climates as determined by the coastal State, taking into account the type of helicopter used, the conditions of wind, turbulence, sea state, water temperature and icing conditions, the helideck should meet the following requirements:

  • .1 The helideck should be of sufficient size to contain a circle of diameter equal to RD. In the case of MODUs expected to be routinely serviced by tandem main rotor helicopters, the helideck should be of sufficient size to contain a circle of diameter equal to at least 0.75 LD.

  • .2 The helicopter deck should have an obstacle-free sector of at least 180° free of obstructions. The reference point for this sector should be a point on the periphery of the circle referenced in paragraph 13.3.3.1, as shown in figure (13-4).

  • .3 The limited obstacle sector should extend out to a distance of 0.83 RD for general operating areas. This distance should be measured from the centre of the helicopter deck. Obstructions in the limited obstacle sector should not extend above a plane measures vertically from the edge of the deck with rise at a rate not exceeding one unit vertically for each two units horizontally from the edge of the helideck (see figure 13-4).

Figure 13-4 Helideck obstacle limitation sector
180° for moderate climate

  13.3.4 The helideck should have a skid resistant surface.

  13.3.5 Where the helideck is constructed in the form of a grating, the underdeck should be such that the ground effect is maintained.

Parent topic: Chapter 13 – Helicopter Facilities footnote
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