Interim requirements for flight testing etc. were:
45m full loadbearing strength + 7.5m shoulders giving 60m.
Additional pair of 7.5m shoulders should be provided to avoid FOD ingestion and provide support for fire and rescue equipment. Takes you to 75m
Full code F requirements
Minimum 60m full loadbearing. Shoulders of 7.5m recommended to give overall minimum of 75m.
Obstacle free zone shall extend to at least 77.5m either side of centreline.
All sorts of other requirements regarding distance. particularly important when 2 'Code F' aircraft could be operating simultaneously.
G