ATCO2
Thanks for taking the time to reply to my points - its appreciated. I'll try and answer all your queries...
First of all, ASAS spacing is NOT a visual approach - its merely using that procedure (the US version) as a starting point in the analogy. I asked the original question because I'm not happy with that analogy.
ASAS spacing deals with ToD through to IAF/FAF. It is also an instrument procedure. Obviously, we specify conditions on the ASAS procedure - the only variable being transferred to the flightdeck here is the implementing and maintaining of a set SPACING behind a target aircraft... both aircraft would have to be following the same STAR, or direct WPT clearance. Also, both aircraft would have to have similar approach performance profiles (not too difficult - most a/c on approach are able to maintain similar speeds - the odd Dash-8 or whatever could be slotted in as necessary).
At all times, the controller will be responsible for designing the solution (to the sequencing problem)... the pilot will only be responsible for implementing it. For example, there may be converging aircraft from 2 different STARs at a single IAF... the ASAS spacing instruction would allow a pilot to identify the target aircraft (possibly 50NM away at this point), input the desired spacing at the IAF passed by the ATCO, and then fly the aircraft (manual or autothrottle) to get to the IAF that distance behind the target a/c (algorithms will help in calculations here - this will be hooked up to the FMS). This would then negate the need for vectoring or speed instructions by the controller for that aircraft (trials HAVE been done - it does virtually negate these types of communication for a busy Extended TMA).
"Less buffers" means less additional spacing used in case of garbled comms / busy VHF etc. There may be a number of time critical instructions that have to be given in the current airspace - this will decrease if the controller takes advantage of this tool.
It's important to note that this is a controller tool - you guys could use it as and when you like. We're not trying to design something here that will threaten you - just help you.
Hopefully, Scott's reply shows where the difference in terminology lies - and the different attitudes towards visual clearances (i.e. successive visual approaches used in the States).
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?
I meant for visual
clearances, not for the ASAS spacing
instruction. They are two very separate entities - possibly I've confused things by mentioning the two together. ASAS spacing will build on the usefulness of visual approaches, but use IFR and no transfer of separation responsiblity.
To answer some of the mountain of questions in the penultimate paragraph (!)
- the controller does the sequencing.
- instructions will be passed at first by VHF voice (with information on a/c being uplinked by ADS-B, a new datalink technology in use worldwide). It is hoped that eventually something very similar to CPDLC will be used.
- in marginal (read bad!) wx, the controller would not offer the procedure... since it is an IFR procedure, it can be done in IMC though (doesn't rely on visual acquisition of the traffic).
- ATCOs maintaining competence is one of the issues that human factors people are currently looking at... since it is only a tool, vectoring can still be used if the ATCO wants.
- pilots and controllers would be trained in this procedure. On the tech-log forum, there is a worrying post about CPDLC - that some airlines train their pilots in using it, and some don't. This shouldn't happen.
- ICAO aren't suggesting it... amongst others, virtually all the European CAAs, EUROCONTROL, the FAA, NASA etc etc are working at developing ASAS procedures to be implemented circa 2005.
I hope this has helped in the understanding... carry on replying everyone - its something that WILL happen sooner rather than later.