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Mobile Installations and Vessels: Movement of Helidecks
Incident Date: --- Time: ---
Type of Activity: Transport - Air
1. The purpose of this notice is to make the offshore oil and gas industry aware of an amendment to the revised version of the Civil Aviation Publication (CAP) 437, Offshore helicopter landing areas: guidance on standards.
2. Following an investigation into a fatal accident which occurred on the helideck of a diving support vessel, in which the movement of the vessel was a contributing factor, the Air Accidents Investigation Branch (AAIB) of the Department of Transport made recommendations to improve safety.
3. The Civil Aviation Authority (CAA) has considered these recommendations and has subsequently incorporated an amendment into the revised CAP 437.
4. The amendment to CAP 437, chapter 6, 'Helicopter landing areas - miscellaneous operational standard', comprises additional text to be added at section 3, 'vessel movement' in sub sections 3.2, 3.3 and 3.4 as follows: 3.2. Pitch and roll reports to helicopters should include values, in degrees, about both axes of the true vertical datum (ie relative to the true horizon) and be expressed in relation to the vessel's head. Roll should be expressed in terms of 'left' and 'right'; pitch should be expressed in terms of 'up' and 'down'; heave should be reported in a single figure, being the total heave motion of the helideck rounded up to the nearest metre. Heave is to be taken as the vertical difference between the highest and lowest points of the helideck movement. The parameters reported should be the maximum peak levels recorded during the ten minute period prior to commencement of the helicopter deck operations. The helicopter pilot is concerned, in order to make vital safety decisions, with the amount of 'slope' of the landing surface and it is therefore important that the roll values are only related to the true vertical and do not relate to any 'false' datum (ie a 'list') created, for example, by anchor patterns or displacement. 3.3. Radio Messages A standard radio message should be passed to the helicopter which contains the information on helideck movement in an unambiguous format. This will, in most cases, be sufficient to enable the crew to make safety decisions. Should the helicopter crew require other motion information or amplification of the standard message, the crew will request this (for example, yaw and heading information).
STANDARD REPORT EXAMPLE
Situation: The maximum vessel movement (over the preceding ten minute period) about the roll axis is 1o to port and 3o to starboard (ie this vessel may have a permanent list of 1o to starboard and is rolling a further 2o either side of this 'false' datum). The maximum vessel movement (over the preceding ten minute period) about the pitch axis is 2o up and 2o down. The total maximum heave (recorded over the preceding ten minute period) is 1.5 metres.
Report: 'Roll one degree left and three degrees right; pitch two degrees up and two degrees down; heave two metres.' 3.4. Current research has indicated that vessel movement is complex in nature and is characterised by a number of parameters, some of which are not presently reported. It is therefore possible that future requirements will contain different measuring and reporting criteria.
Safety Alert number: 68
Whilst every effort has been made to ensure the accuracy of the information contained in this publication, neither the IOGP nor any of its members past present or future warrants its accuracy or will, regardless of its or their negligence, assume liability for any foreseeable or unforeseeable use made thereof, which liability is hereby excluded. Consequently, such use is at the recipient's own risk on the basis that any use by the recipient constitutes agreement to the terms of this disclaimer. The recipient is obliged to inform any subsequent recipient of such terms.