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Tiedowns should be designed to accommodate helicopters routinely using the helideck and for helicopters which may use the helideck in case of an emergency.
9.11.3.2 Structural strength
Where deck penetrations for tie-down points are located, adequate structural strength should be provided in the helideck surface and the tiedown fittings to accommodate the anticipated loads.
Tiedown strops are normally rated in the order of 5000 kg (approximately 11200 lbs).
9.11.3.3 Drainage
Adequate drainage of the deck penetrations / tiedown fittings should be provided. The drainage holes should be of sufficient size to avoid blockages and where it is necessary to prevent fuel spillage etc. onto the areas below the helideck, removable plugs should be fitted to seal the helideck surface. Sealing the helideck surface is important where the helideck is mounted above an accommodation area or the bridge of a vessel.
9.11.3.4 Tiedown fittings
There are different designs of tiedown fitting and they may be permanent or removable. In both cases, the diameter of the bar or loop for attaching the tiedown strop should not exceed 22 mm.
On an existing helideck where the bar or ring diameter exceeds 22 mm and is therefore too large for the tiedown strop hook capacity, ‘D’ shackles or some other means will be required to provide the necessary connection. Proper storage and maintenance of these additional fixings in a location adjacent to the helideck will be an operational requirement.
Permanent fittings
The designs of permanent tiedown fittings are generally:
.
A recessed box with a cross bar (See Figure 9.15), or
.
A semi-recessed ring assembly.
(Photo courtesy of John Burt Associates Limited)
Removable Fittings
Removable fittings may be:
.
Threaded rings, or
.
Special block type fixings (normally used on perforated ‘passive’ helideck surfaces.
When using removable tiedown fittings, there will be an essential operational requirement to provide proper storage for the fixings in a secure location adjacent to the helideck. Also, an adequate number of replacements should be made available and the fixings (helideck surface attachment and the fittings) will require routine maintenance and checking. Additionally, where removable tiedown fittings are used, it is prudent to provide painted markings around the correct locations where the fittings are to be positioned, when in use.
An essential design feature of any tiedown system and the fittings is to ensure that they do not damage aircraft tyres or cause a personnel trip hazard. Permanently fixed, surface mounted, tiedown rings are not acceptable. This type of fixing can easily damage aircraft tyres and cause a personnel trip hazard.
Also, recessed boxes that are too large can cause an aircraft wheel to become lodged in them during routine helideck operations or in situations when manoeuvring the helicopter off of the landing area.
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