A/p failure(Disconnection) followed by manual takeover of controls AND LANDING requires an RVR of 350metres as per our company policy. If RVR is not 350 or above its a GA.
For a b777 Master Caution is inhibited below 200RA except for NO AUTOLAND
AUTOTHROTTLE SPEEDBRAKE AUTOPILOT
Should you get a AUTOPILOT msg with 75m RVR it's just GA.
Personally have been in a situation where RVR reported 100-150 Metres and have lost complete sight of runway (due fog patches) for few secs (both on takeoff and landing in night time) and lesson learnt that situation can become very dicey.
Should one try to manually takeover and land, I wouldnt trust 75m RVR will give much visual reference.