Annex B – Technical Appraisal

B-1        This annex discusses the key technical issues raised in Section 3.4 of the main body of the Project Memorandum. It is not intended to cover the full breadth of work carried out by Atkins in the feasibility study, but instead to set out the main technical issues and show how these have been addressed in project design. Further detailed technical information is available in Section 7 and Appendices H, I, J, K, L, M, N, O, P, Q and R of Atkins’ Final Report.

Development of Options

B-2        Initial feasibility work carried out by Atkins in early 2004 examined a wide range of options for maintaining access to St Helena , both by sea and by air.  In carrying out this work Atkins took account of previous studies, approaches from the private sector, and suggestions from private individuals. The air options included consideration of an airship, amphibious planes, small business jets and medium-sized passenger aircraft, providing services from Ascension Island , South Africa and Europe . Sea options included a mixed passenger and cargo vessel similar to the RMS St Helena, the potential to utilise the cruise market, a dedicated passenger-only ship, and a “fast ship”.  Each option was assessed to determine whether it satisfied three key criteria, namely:

·          whether the option is technically feasible

·          whether it meets HMG's/SHG's commitment to maintaining access to St Helena

·          whether it is likely to increase GDP on St Helena to such an extent that increases in government revenue offset any increase in subsidy over ten years

B-3        Options satisfying these criteria were subjected to a comparative assessment against agreed technical, institutional, environmental, economic, financial and social criteria.  It was also a requirement that at least one sea option should be studied in detail, regardless of the overall ranking.  The comparative assessment led to the selection of three options for detailed feasibility work:

·          Development of an aerodrome that can support the safe operation of Boeing 737 or similar aircraft (the ‘long runway’ option)

·          Development of an aerodrome that can support the safe operation of 19‑seater Business Jet aircraft (the ‘medium runway’ option)

·          Replacement of the RMS with another mixed passenger and cargo vessel

B-4        Further details of the short-listing process can be found in Atkins’ June 2004 Options Paper, an edited version of which was made available to the public in the UK and St Helena .

Development of Sea Options

B-5        Considerable work has previously been done to develop the specification of an appropriate replacement to the RMS, both at the time of design of the current ship, and during the 2001 High Point Rendel (HPR) Comparative Study.  Atkins’ feasibility work confirmed previous conclusions that the unique requirements of St Helena, in particular the relatively small passenger and freight volumes, and the need for the ship to operate in the seas of the South Atlantic, necessitate the provision of a purpose-built mixed passenger and cargo vessel. Specifications were proposed by HPR in their final report, which maximised tourist revenue while serving the island’s needs. These were adopted for the feasibility study.

Development of Air Options

B-6        A number of previous studies have looked at air access at a conceptual level, identifying the most likely sites for construction of a runway on St Helena and identifying possible air service options.  More detailed work was carried out by private sector consortia in response to SHG’s April 2003 international invitation, but there remained a number of issues that required further investigation and analysis before it was possible to confirm the technical viability of establishing air access.

B-7        Atkins’ feasibility work provides a high level of confidence that a suitable runway can be constructed on Prosperous Bay Plain to support air services to Ascension Island , South Africa and beyond. Atkins have undertaken original topographic and geotechnical survey work on Prosperous Bay Plain, carried out laboratory testing, established meteorological monitoring to confirm weather conditions at the site, and worked in close collaboration with ASSI to develop viable technical options for the two short-listed air options.  In carrying out this work, Atkins have gone into a greater level of detail than would normally be associated with a feasibility study, developing outline designs and schedules of quantities. The designs have been subjected to both internal and external checks, and the assistance of experienced quantity surveyors called upon to establish cost estimates. This work has confirmed the technical feasibility of constructing a runway capable of supporting safe operations by aircraft up to the size of a Boeing 737-800 or equivalent on Prosperous Bay Plain.

Runway Design

B-8        In the context of the mountainous topography of St Helena , the Prosperous Bay Plain site is a relatively flat area, sited approximately 300m above sea level to the east of the island and extending some 1,700 m in an approximately north-south direction. Beyond this to the north the ground falls away sharply to Prosperous Bay , and to the south lies Dry Gut, a steep-sided valley that cuts across the plain. In addition, there is high ground to the north (the Haystack and the Barn) and to the south (Great Stone Top). This topography places tight constraints on the design of a runway, and much of the design work has focused on achieving a runway length and alignment that will satisfy the requirements of the air regulator, provide sufficient length for safe operations and which minimises capital expenditure. Plate B.1 is a panorama of the site of the proposed runway on Prosperous Bay Plain, viewed from the west.  Plate B.2 shows the runway alignment looking south towards Great Stone Top.

Plate B.1                    Panorama of Prosperous Bay Plain

Plate B.2                    Runway Alignment facing South

  B-9        A major factor in determining the cost of any runway is the requirement for Runway End Safety Areas (RESAs). ASSI indicated that, given the remoteness of the location and the difficult nature of the terrain on the approaches, they would be unwilling to accept anything less than the minimum required by Annex 14 of the Civil Aviation Procedures (CAP).  This is 120m for a Code 2 runway, and 240m for a Code 3 runway.

B-10      The concept behind the design of the ‘medium runway’ was the safe operation of 19‑seat business jets, preferably utilising a Code 2 runway.  On closer analysis, the length of runway required for take-off to Cape Town for this type of aircraft is between 1,340m and 1,400m, well in excess of the 1,199m maximum for a Code 2 runway.  As a result, the ‘medium runway’ would be classified as Code 3, and the longer RESAs required. The key conceptual benefit of the ‘medium runway’ was to avoid the need for expensive construction out into Dry Gut, but classification as a Code 3 runway makes this impossible. 

Plate B.2 Northern Approach

B-11      The total estimated cost for construction of the ‘medium runway’ is ██████. A further ██████ would be required after approximately 20 years of operation to upgrade the fuel supply system.

B-12      Use of one of the RESAs for take-off would extend the Code 3 ‘medium runway’ available take-off length to 1,674m. Consideration was given to limited operations by Boeing 737 or similar aircraft on this runway. While it is technically feasible to operate Boeing 727-600 and 737-700 aircraft from a slightly modified ‘medium runway’, performance limitations are likely under cross wind conditions, and the majority of operations would be runway-limiting. ASSI have expressed an opinion that this increases the risk of an undershoot or overshoot on landing, and as a result they might consider imposing further limitations on aircraft operations. The ‘medium runway’ would not be able to support significant air cargo operations.

B-13      The above, combined with the lack of market interest in a service operated by business jets and lack of flexibility of air operations that could be supported by the ‘medium runway’, made this option unattractive in comparison to the ‘long runway’.

B-14      The recommended option is therefore construction of a ‘long runway’ with a total runway length (including RESAs and end strips) of 2,250m, capable of supporting the safe operation of Boeing 737-800 or similar aircraft. By making the runway one-directional for take-off it is possible to achieve a Take-Off Run Available (TORA) of 1,925m and a Landing Distance Available (LDA) of 1,650m, allowing unrestricted operations of the design aircraft, while minimising the extension of the runway into Dry Gut. This option provides maximum flexibility for both passenger and air cargo operations. Figure B.1 illustrates the key features of the proposed runway.

Figure B.1              Long Runway Take-Off and Landing Distances

B-15      The total estimated cost for construction of the ‘long runway’ is ██████, assuming the use of a traditional procurement approach. As with the ‘medium runway’, a further ██████ would be required after approximately 20 years of operation to upgrade the fuel supply system.

B-16      Detailed civil engineering design will be carried out as one of the first activities of project implementation. Design will be in accordance with Annex 14 of the Civil Aviation Procedures (CAP), which is a statutory requirement under the ICAO Air Navigation Orders (ANO). In due course, this will permit the airport to be certified under the ANO ( Overseas Territories ) Order.  Figure B.2 presents the general layout of the ‘long runway’ developed by Atkins in consultation with ASSI.

Figure B.2              Long Runway General Layout

Continued

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