I see a huge problem here with "Everybody Knows", even among the people who sound like air transport professionals. Lufthansa Requirement: Instrument landing

I see a huge problem here with "Everybody Knows", even among the people who sound like air transport professionals. Lufthansa Requirement: Instrument landing SFO Preference: Visual landing Reason for Lufthansa requirement: IFR/ILS is safer than visual Reason for SFO preference: Visual allows more planes with lower separation, leading to better throughput. More context: Lufthansa would be using their instruments anyway, without declaring instrument flight rules landing. Declaring ILS in some generic sense is "safer", but specifically it means that the controllers cannot clear them to land in a degraded ILS environment, where perhaps some beacons are offline. The SFO preference is not just something that the airport or the controller decided - it's also good for the airlines and the flying public. More planes land faster. The planes took off with the expectation that they would be able to land at a certain rate; otherwise they wouldn't schedule them to arrive so frequently. The problem with "Everybody Knows" is that you really don't. The controller may assume that Lufthansa means "hey are all the beacons on?" when they say "IFR landing". Lufthansa may assume that IFR clearance means that the ILS equipment is operational, but that they can still fit into the VFR sequence. In this case, those assumptions probably would have worked out Ok. But if "Everybody Knows" is part of your work culture and you work on life critical systems, than someone will eventually die, as you can see from the history of investigations into air transport incidents. If you feel like someone is saying or implying "Everybody Knows" in a safety critical or life critical system, that is bad culture. Start documenting.