Hi Rat 5,
Now the average ATC tower is 30m high. How can this relate to pilot eye height over rwy?
Because the RVR measuring devices are located to the side of the runway, (on the grass normally) and stand about 2m high.
Runway visual range - Wikipedia, the free encyclopedia
There was a Vanguard crash at LHR in the 60s (
ASN Aircraft accident Vickers 951 Vanguard G-APEE London-Heathrow Airport (LHR)), caused by attempting to do a manual landing in fog. After that accident the rules changed to stop other keen aviators from going down to "have a look".
If the reported RVR is below minima, and you have not passed the OM (or equivalent point or 1,000 ft AAL) - even if you can see through the shallow fog 10 miles out, then it's what we in the trade call an "Approach Ban".
Edit: See Follow up/ Safety action note 4.
"The system whereby no positive approval of an operator's weather minima is required to be given by the Ministry is unsatisfactory. It gives power whilst withholding responsibility. Positive approval or disapproval should be required."
So you may thank these guys for the increased operating safety by taking the decision to make the approach or not, by the OM (or equivalent position).