Hi Too Few Stripes,
.... if you can provide a reference?
Sorry - I can't. Under Failed or Downgraded Equipment our FCOM used to say
"Touchdown zone RVR assessment system:
May be temporarily replaced with midpoint RVR if approved by the State
of the aerodrome. RVR may be reported by human observation."
However it still says "The touchdown zone RVR shall always be controlling.
If reported and relevant, the midpoint and stop end RVR shall also be controlling."
If you are allowed to commence an approach with Touchdown RVR missing (but mid point & stop end reported), how can you satisfy "touchdown RVR shall always be controlling" unless the reported mid point RVR => touchdown zone requirement?