I came across an interesting note on the Met Office website here:
http://www.metoffice.gov.uk/media/pd...wind_shear.pdf
They did a study entitled "Assessing climatology and wind shear risk for a new airport" some time ago.
To quote part of it:
"Assessment of the wind shear risk was found to be
relatively low. However we were able incorporate other findings arising from our analysis to highlight other risks that were not previously anticipated. This included crosswind risks and the potential of wind shear
close to the surface, due to possible effects on localised air flow from the wind coming up off the steep coastline.
Analysis provided bespoke information for St Helena Airport, including a range of crosswind thresholds associated with specific aircraft types that are planned to be operational at this airport, in both dry and wet conditions.
Recommendations were made for the need for more observational equipment in close proximity to the runway to fully understand the more localised wind risks near the surface. The first would be to install an additional anemometer or windsock at the centre point of the runway as well as a windsock within sight of the Air Traffic Control tower to help identify if turbulent flow is evident."
So they foresaw the likely wind shear "close to the surface" which was so clearly evident when the Comair flight landed. I'm not sure if the extra windsock and anemometer have been installed though.
And further reading on GBAS has come up with particular worries for stations in the equatorial region. Rapid ionospheric changes near the equator can cause large changes in GPS propagation second by second under some circumstances, at such a rate that the augmentation (correction) signals cannot keep pace with. This would reduce the improvement in GPS accuracy that the GBAS system is supposed to provide.
It may be that ASSI will want an extended period of testing of the system on St Helena so that they can see how often this degradation of accuracy is likely to occur. In any case, it seems that extending the system to Cat II/III status looks very difficult in the equatorial region so there will be little advantage over the LOC/DME approach that's already available, which, like GBAS, offers Cat I minimums.
I think that SHG will have to come up with an air service provider soon - otherwise I can see the Public Accounts Committee taking a look at what that quarter of a billion has been spent on.