Simultaneous Offset Instrument Approach, with its offset and inclined localiser(or "pseudo-localiser" using LAAS) and in combination with an advanced airfield radar and display (PRM) has been in operation since 2004, starting at SFO. Prior to that paired IFR approaches were allowed only if the runways were at least 4300ft apart, although this was reduced to 3500ft with PRM.
SOIA is capable of providing some IFR assistance to runways as close as 750ft. There are some severe limitations(a)the decision height for the trailing aircraft is 2100ft, atwhich point the localiser tracts are 3000 ft,and the trailing pilot has to execute a visual lateral manoevre to align with his/her runway.SOIA conditions at SFO only exist for about 5% of time. For78% the whole the whole approach is VMC, while for 18% SOIA cannot cope.(b)the combined arrival rate is omly about 25-30% greater than for a single runway. My guess is this because each must consist of a "non-heavy" leader and "heavy" follower because of wake encounter problems during the visual phase. This would give rise to sequencing problems.
There is only one way to lick the IFR problem for good, and it requires two features(1)autopilot with"tunnel-in-the-sky"mode("pseudo-ILS" has large flight technical error at long range)(2)HUD for trailing pilot which promtly shows any"blundering " by the leader. This requires ADS-B IN.
Both of these systems require "safety-of-life" integrity, and we know from CatIII autoland experience that this takes time ,involving such things as simulation, flight trials (including in-service trials in VFR conditions) and development of operating procedures.FAA show no sign of going down this route in the near future, or even encouraging others to do so.
BTW I am neither a pilot or controller
Keith
