Quote:
Originally Posted by Hugh Jarse
Nigel, a runway lights count is only valid for RV, as opposed to the RVR measured by instruments. 
David N, fog often has clearer patches as it moves through, and Asiana may have been lucky to be arriving at the time when this was happening.
If I were a cynic, I might say they just autolanded with the prevailing conditions anyway  But that wouldn't be nice  |
Hugh, before the installation of transmissometers at Sydney it was widely accepted that the RELC's (runway edge light counts) we did
were the RVR. When the transmissometers were ready to be commissioned, comparisons were made between the electronically measured RVR and the RV we were making using RELC's. It turns out our RELC's were fairly accurate!
Obviously, in the event of a transmissometer failure, RELC's are used as a back-up method of determining visibility.