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Old 13th Mar 2016, 14:08
  #87 (permalink)  
Broken Biscuits
 
Join Date: Dec 2015
Location: West Midlands UK
Posts: 38
New info on relocated navaids at St Helena

I have found some information on the new positions of the relocated navaids at St Helena Airport. The localizer antenna is now located much closer to the runway (as before, on the inland side) at the edge of the levelled strip, and its offset has been reduced from about 15 to 5 degrees.

The runway has a magnetic heading of about 196 degrees (from Google Earth and the magnetic variation) therefore the beam now gives an approach heading of about 201 degrees magnetic.

The VOR has been relocated on the same side as the localizer, approximately abeam the midpoint of the runway and about 850m directly behind the localizer antenna, so that the approach heading for a VOR/DME approach will be the same as that for the localizer/DME approach. It's interesting that with the reduced approach offset, the consequences of a late decision to go around from an approach have been significantly reduced.

The previous 15 degree offset had the aircraft heading directly for the high ground to the west of the runway (i.e. inland from the control tower/terminal) so a late decision to go around could have been catastrophic. By continuing on the new approach of 201 degrees magnetic, the aircraft should easily clear the high ground and get back safely over the sea, even if the left turn missed approach procedure is delayed.

The new position of the VOR may still problematic, however. Someone has already mentioned the metal security fence - this would almost certainly be a problem, running as it does (did?) parallel to the runway, just right to give a nice reflection out onto the approach path to runway 20. But its new location is even more of a problem for the opposite approach to runway 02. There are the terminal and combined buildings, fire rig and all sorts of metalwork out in that direction, and in particular the apron where any parked aircraft could cause reflections. So it may be that the VOR/DME approach to runway 02 will be unusable.

Since there is no localizer for runway 02, that only leaves a non-precision NDB/DME approach. However, this may be perfectly acceptable, as the prevailing winds probably mean that landing from the southerly direction will be extremely rare. (The NDB by the way has not been relocated, as far as I know - it is on the seaward side of the runway, roughly opposite the apron location.)

Of course, the ground based augmented satellite system (GBAS) has the possibility of providing good guidance to both runway directions. However, at present this is FAA certified to Category 1 only, the same as the localizer/DME approach, although in time this may be improved upon. But GBAS is dependent on ASSI approving its use. As far as I can tell from the Honeywall website, no UK overseas territory has yet had a GBAS system installed, so St Helena will be a first for ASSI to approve. (Oh, decisions, decisions!)

The recent announcement of the acquisition by COMAIR of a new aircraft for the St Helena route implied that it was fitted with "special" electronic navaid equipment - I assume this refers to the GBAS functionality needed to take advantage of the St Helena installation.
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