malcolmfrost wrote:it doesn't matter as long as everyone's on the same pressure setting.
That's the key issue, but I would expand it. The objective should be that airport operations anywhere, any airport, any country should be conducted with minimal variation in procedure, and altimeter settings should require as little communication as possible. Ideally ATIS, ASOS or similar should supply the the altimeter setting with no need for ATC or equivalent to supply it for VFR aircraft. If there is terrain near the circuit (my base has a 1600 ft high hill within the circuit) the charted altitude of the hill should match the altitude on the altimeter. Same for airspace delineations. If the runway is at high altitude, that should be unimportant. If ATC has radar (either at the airport or approaching the airport, and regardless of which ATC any given plane is talking with) and is it using it to advise multiple pilots of other traffic there should be no need for ATC to consider altimeter settings in use by different aircraft or different ATC facilities in the same area. If two pilots/aircraft are coordinating their separation on an air-to-air frequency they should not have to discuss altimeter settings. Everybody in the entire area, whether operating at the airport, passing over the airport or anywhere near should be on a altimeter setting that matches every other aircraft and every charted geographic or airspace feature in the area.