Section 5 Helicopter landing areas
Clasification Society 2024 - Version 9.40
Clasifications Register Rules and Regulations - Rules and Regulations for the Classification of Ships, July 2022 - Part 3 Ship Structures (General) - Chapter 9 Special Features - Section 5 Helicopter landing areas

Section 5 Helicopter landing areas

Parent topic: Chapter 9 Special Features

5.1 General

5.1.1 Attention is drawn to the requirements and guidance of National and other Authorities concerning the construction of helicopter landing platforms and the operation of helicopters as they affect the ship. These include SOLAS Regulation 18 - Helicopter facilities and Reg.III/28 as applicable. as well as the International Chamber of Shipping (ICS) Guide to Helicopter/Ship Operations and the International Aeronautical Search and Rescue Manual (IAMSAR) and CAP437 Standards for Offshore Helicopter Landing Areas.

5.1.2 Where the requirements of this Section have been adhered to for a designated helicopter landing platform or other deck area and fire-fighting appliances and other equipment necessary for the safe operation of helicopters are provided, the ship will be eligible for the special features notation Helideck. See also SOLAS Regulation 18 - Helicopter facilities.

5.1.3 Where the requirements of this Section have been complied with for an area on a ship designated for occasional or emergency landing of helicopters, the ship will be eligible for the special features notation Occasional Helicopter Landing Area, see SOLAS Regulation 18 - Helicopter facilities.

5.1.4 The structure is to be designed to accommodate the largest helicopter type which it is intended to use.

5.1.5 Plans are to be submitted showing the proposed scantlings and arrangements of the structure. The type, size, weight and footprint of helicopters to be used are also to be indicated. Details of the helicopter types to be used are to be included in the Loading Manual (see Pt 3, Ch 4, 8.2 Loading Manual)

5.1.6 Where the landing area forms part of a weather or erection deck, the scantlings are to be not less than those required for decks in the same position.

5.2 Symbols

5.2.1 The symbols in this Section are defined in Pt 3, Ch 9, 1.2 Symbols and in the appropriate sub-Section.

5.3 Arrangements

5.3.1 The landing area is to be sufficiently large to allow for the landing and manoeuvring of the helicopter, and is to be approached by a clear landing and take-off sector complying in extent with the applicable Regulations, International Standards, or to the satisfaction of the National Authority.

5.3.2 The landing area is to be free of any projections above the level of the deck. Projections in the zone surrounding the landing area are to be kept below the heights permitted by the Regulations, International Standards, or to the satisfaction of the National Authority.

5.3.3 Suitable arrangements are to be made to minimise the risk of personnel or machinery sliding off the landing area. A non-slip surface and anchoring devices are to be provided.

5.3.4 Engine uptake arrangements are to be sited such that exhaust gases cannot be drawn into helicopter engine intakes during helicopter take off or landing operations.

5.4 Landing area plating

5.4.1 The deck plate thickness, t, within the landing area is to be not less than:

t = t 1 + 1,5 mm
where
t1 =
α = thickness coefficient obtained from Figure 9.3.1 Tyre print chart
β = tyre print coefficient used in Figure 9.3.1 Tyre print chart
=
s = stiffener spacing, in mm
k = material factor as defined in Pt 3, Ch 9, 1.2 Symbols for steel members

The plating is to be designed for the emergency landing case taking:

P 1 = 2,5 φ 1 φ 2 φ 3 fγ P w tonnes

in which φ 1, φ 2, φ 3 are to be determined from Table 9.3.1 Deck plate thickness calculation

f = 1,15 for landing decks over manned spaces, e.g. deckhouses, bridges, control rooms, etc.
= 1,0 elsewhere
P h = the maximum all-up weight of the helicopter, in tonnes
P w = landing load on the tyre print in tonnes;
for helicopters with a single main rotor, P w is to be taken as P h divided equally between the two main undercarriage wheels
for helicopters with tandem main rotors, P w is to be taken as P h distributed between all main undercarriage wheels in proportion to the static loads they carry
For helicopters fitted with landing gear consisting of skids, P w is to be taken as P h distributed in accordance with the actual load distribution given by the airframe manufacturer. If this is unknown, P w is to be taken as 1/6P h for each of the two forward contact points and 1/3P h for each of the two aft contact points. The load may be assumed to act as a 300 mm x 10 mm line load at each end of each skid when applying Figure 9.3.1 Tyre print chart.
γ = a location factor given in Table 9.5.1 Location factor

For wheeled undercarriages, the tyre print dimensions specified by the manufacturer are to be used for the calculation. Where these are unknown, it may be assumed that the print area is 300 x 300 mm and this assumption is to be indicated on the submitted plan. For the tyre print area of a group of wheels, see Pt 3, Ch 9, 3.5 Deck longitudinals and beams 3.5.3.

For skids and tyres with an asymmetric print, the print is to be considered oriented both parallel and perpendicular to the longest edge of the plate panel and the greatest corresponding value of α, taken from Figure 9.3.1 Tyre print chart.

Table 9.5.1 Location factor

Location γ
On decks forming part of the hull girder    
(a) within 0,4L amidships 0,71 Values for intermediate locations are to be determined by interpolation
(b) at the F.P. or A.P. 0,6 Values for intermediate locations are to be determined by interpolation
Elsewhere 0,6  

5.4.2 The plate thickness for aluminium alloy decks is to be not less than:

t = 1,4t 1 + 0,5 mm

where t 1 is the mild steel thickness as determined from Pt 3, Ch 9, 5.4 Landing area plating 5.4.1.

5.5 Deck stiffening and supporting structure

5.5.1 The helicopter deck stiffening and the supporting structure for helicopter platforms are to be designed for the load cases given in Table 9.5.2 Design load cases for deck stiffening and supporting structure. The helicopter is to be positioned so as to produce the most severe loading condition for each structural member under consideration.

5.5.2 The minimum requirements for secondary stiffeners are to be in accordance with the requirements of Table 9.3.4 Secondary stiffener requirements using the UDL and helicopter patch loads given in Table 9.5.2 Design load cases for deck stiffening and supporting structure. The structural design factors, fσ and fτ, are to be taken as the permissible bending and shear stresses given in Table 9.5.3 Permissible stresses for deck stiffening and supporting structure divided by the specified minimum yield and shear strengths of the material respectively.

5.5.3 The minimum moment of inertia, , of aluminium alloy secondary structure stiffening is to be not less than:

where Z is the required section modulus of the aluminium alloy stiffener and attached plating and ka as defined in Pt 3, Ch 9, 4.6 Pontoon webs and stiffeners 4.6.2.

5.5.4 When the deck is constructed of extruded aluminium alloy sections, the scantlings and connections between structural members will be specially considered.

5.5.5 Where a grillage arrangement is adopted for the platform stiffening, and for the truss structures supporting a helicopter landing area, it is recommended that direct calculation procedures be used in association with the permissible stresses given in Table 9.5.3 Permissible stresses for deck stiffening and supporting structure.

5.5.6 Where the helicopter landing area is supported by truss structures, the deck in way of the bottom of the truss structures is to be assessed for the loads imposed by the helideck, in accordance with Table 9.5.3 Permissible stresses for deck stiffening and supporting structure.

5.6 Bimetallic connections

5.6.1 Where aluminium alloy platforms are connected to steel structures, details of the arrangements in way of the bimetallic connections are to be submitted.

Table 9.5.2 Design load cases for deck stiffening and supporting structure

  Loads
Load case Landing area Supporting structure
(See Note 1)
  UDL, in kN/m2 Helicopter
patch load
(See Notes 2 and 3) 		Self-weight Horizontal load
(See Notes 2 and 4)

(1) Overall distributed loading

 2
— — —

(2) Helicopter emergency landing

 0,5
2,5P w f W h 0,5P h

(3) Normal landing

 0,5
1,5P w W h 0,5P h + 0,5W h
Symbols
P h and P w as defined in Pt 3, Ch 9, 5.4 Landing area plating 5.4.1
UDL = Uniformly distributed vertical load over entire landing area
W h = structural self-weight of helicopter platform

Note 1. For the design of the supporting structure for helicopter platforms, applicable self weight and horizontal loads are to be added to the landing area loads.

Note 2. The helicopter is to be so positioned as to produce the most severe loading condition for each structural member under consideration.

Note 3. For the emergency landing and normal usage load cases, the helicopter patch load is to be increased by a suitable structural response factor depending upon the natural frequency of the helideck structure. This factor is to be taken as 1,3 unless calculations are submitted justifying a lower factor. In cases where the Occasional Helicopter Landing Area notation is to be assigned, this factor can be taken as 1,0. For helidecks constructed of aluminium alloys, the value of the structural response factor is to be specially considered.
Note 4. For the design of stiffening and truss support structures supporting a helicopter landing area, appropriate wind loads shall be considered for all load cases in accordance with Pt 3, Ch 9, 9.2 Loading, where the wind speed is to be taken as 31 m/s. The wind direction, together with the horizontal imposed load (if applicable), is to produce the most severe loading condition for each structural component considered.

Table 9.5.3 Permissible stresses for deck stiffening and supporting structure

  Permissible stresses, in N/mm2 (see Notes 1 and 2)
Load case
(See Table 9.5.2 Design load cases for deck stiffening and supporting structure) 		Deck secondary structure (beams, longitudinals)
(See Note 3) 		Primary structure (transverses, girders, pillars, trusses) All structure
  Bending Combined bending and axial Shear

(1) Overall distributed load




0,6σc

(2) Helicopter emergency landing



0,9σc

(3) Normal landing




0,5σc
Symbols
k = a material factor:
= as defined in Pt 3, Ch 9, 1.2 Symbols for steel members
= k a as defined in Pt 3, Ch 9, 4.6 Pontoon webs and stiffeners 4.6.2 for aluminium alloy members
σc = yield stress, 0,2% proof stress or critical buckling stress, in N/mm2, whichever is the lesser

Note 1. For strength deck longitudinals and girders, the permissible bending stresses are to be reduced as follows:

Note (a) within 0,4L of amidships - by 30%

Note (b) at the F.P. or A.P. - by 0%

Values at intermediate locations are to be determined by interpolation between (a) and (b).

Note 2. For helicopter landing areas on offshore support vessels, the permissible bending stresses are to be reduced by 20%.

Note 3. When determining bending stresses in secondary structure, for compliance with the above permissible stresses, 100% end fixity may be assumed.

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