I don't see how we can "instruct" a pilot to follow another aircraft on a visual approach when there are so many variables, such as speed differentials, aircraft weight category, even changing weather conditions. We would have to specify conditions, e.g, no further East than 6 DME, or pilots would go on a sightseeing tour, and seriously disrupt the sequence.
Visual approaches can be more expeditious, and pilots welcome the opportunity to actually hand fly their aeroplanes, but in a busy environment they are just not possible. The controllers'workload would not be decreased because he/she would still have to monitor the visual approach situation and still set up the basic sequence. Not being able to accurately plan on a set landing rate would have serious repercussions for capacity. There would be no constant spacing criteria to plan around - even more critical for single runway airports - what final approach spacing would be provided - this HAS to be within the control of the ATCO. "Less buffers added to minimum spacings" - sorry I don't understand this phrase.
We are not giving a "visual clearance" to IFR aircraft! We would only do this if a pilot cancelled his IFR flight plan and went VFR - not very likely with heavy metal in a control zone, and impossible in a Class A control zone. As stated above - a visual approach is STILL an IFR clearance.
"How can the pilot not have the responsibility for separation if he is maintaining that separation, and has been cleared to do so by the controller?" Are we talking a clearance or an instruction here, or are you confused yourself? ATC RTF phraseology for visual approaches is along the lines of, "report if you get the airport in sight and wish to continue visually." The pilot can accept or decline this offer. If he accepts a visual approach, then he is cleared for a visual approach, usually with a condition to report turning base leg or final. He is then normally instructed to contact the tower. (Approach control still retain responsibility for separation). If a subsequent pilot reports he wishes to make a visual approach, he is given traffic information on the aircraft ahead but not actually cleared for the approach until it is safe to do so with regard to vortex wake and speed differentials. In this way ATC retain control of the separation responsibility. I would never allow a second aircraft to make a visual approach unless I was 100% sure he had the correct aircraft ahead in sight. Although not its primary function, pilots are tending to use TCAS to assist them in this respect.
Are you saying that visual approaches are carried out where pilots maintain 2.5 miles from the aircraft ahead? If this is possible with a continuous sequence of aircraft, then perhaps ATCOs are superfluous - I don't think we are at that stage yet. Neither will we be in 2005!
"A more efficient arrival sequence" - does ASAS look at the traffic mix and decide the best sequence of H, M, UM, S, L aircraft, as currently happens? How are the instructions given? Is the pilot given headings to fly, speed instructions and descents by a "magic box" on the flight deck? Or just left to follow another aircraft from a predetermined range from touchdown? Are the approaches flown totally visually, or by the use of an ILS or another precision or non-precision aid? What about light aircraft and helicopters also operating in the zone? 8 nm separation within the TMA is extremely wasteful and would immediately impact upon holding delays. Would the pilots be able to refuse an ASAS clearance in marginal weather? How about ATCOs maintaining competence in vectoring if the pilots are doing it all the time? What about short notice priority approaches - how long would it take to sort out the sequence effectively? What do pilots think abot the increased cockpit workload? There would be vastly differing levels of competence amongst pilots using these procedures.
I would love to put my feet up and "monitor" the situation, but from what you have told me I am far from convinced of the advisability of this initiative. ICAO have lost a lot of credibility with UK ATCOs recently, cf. "taxi to the holding position (runway)" - which caused no end of confusion; anything they are suggesting should be very closely scrutinised. Let's hear some more opinions about this.