We don't use Ausy rules here in blighty - here's a simple table of the arrival spacings I have to apply
Leading.......Following.............Minimum Distance...Minimum Distance
Aircraft.......Aircraft................MATS 1.................London MATS 2
SUPER........SUPER...................4 miles
(A380)........HEAVY..................6 miles
.................MEDIUM................8 miles/3 minutes
.................SMALL..................8 miles/3 minutes
.................LIGHT.................10 miles/4 minutes
HEAVY........HEAVY..................4 miles.................4 miles
.................UPPER MEDIUM.......5 miles.................5 miles
.................MEDIUM................5 miles.................5 miles
.................SMALL..................6 miles................ 6 miles
.................LIGHT...................8 miles.................7 miles
UPPER.........UPPER MEDIUM.......4 miles.................3 miles
MEDIUM.......MEDIUM................4 miles.................4 miles
.................SMALL..................4 miles..................4 miles
.................LIGHT...................6 miles..................6 miles
MEDIUM......MEDIUM................3 miles...................N/R
.................SMALL..................4 miles..................3 miles
.................LIGHT...................6 miles..................5 miles
SMALL........MEDIUM................3 miles..................N/R
.................SMALL..................3 miles..................N/R
.................LIGHT...................4 miles..................3 miles
Upper medium = B757, DC8, B707, IL62 or VC10
N/R - Not required
UK categories by MTOW
Heavy 136000+ kg; Medium 40000-136000 kg; Small 17000-40000 kg; Light -1700kg.
Although these are minima for IFR final approach spacing it is recognised that as aircraft slow down durng the final stages of approach these minima will be slightly erroded so the spacing is normally applied until 4 nm final by use of rigid speed control.
I don't believe that stats are kept of the number of times less than minimum spacing is applied (doesn't happen very often) but pilots are always encouraged to report a vortex wake encounter in order that the phenomenon can be better understood. I'd probably have 2 pilots a year filing a vortex report and that would normally be when the minimum spacing has been applied. The minima are to reduce the likelyhood of a vortex encounter, they do not claim to erradicate all chance of an encounter.
VFR traffic is allowed to self position behind heavier aircraft. We use the phraseology "...caution vortex wake, the recommended spacing is x miles." and allow the pilot to use judgemet as to how much spacing to apply.
Remind me never to try to PPRuNe a table again