Separation between medium following medium on ILS approach must be at least 3 NM since medium behind medium doesn't need increased wake turbulence separation.
The following events require increased separation:
- light behind medium (5.0 NM or 3 minutes)
- light behind heavy (6.0 NM or 3 minutes)
- medium behind heavy (5.0 NM or 2 minutes)
- heavy behind heavy (4.0 NM)
And from DOC4444:
6.7.3.4.3 The minimum radar separation to be provided between aircraft established on the ILS localizer course
and/or MLS final approach track shall be:
a) 5.6 km (3.0 NM) between aircraft on the same ILS localizer course or MLS final approach track unless increased longitudinal separation is required due to wake turbulence; and
b) 3.7 km (2.0 NM) between successive aircraft on adjacent ILS localizer courses or MLS final approach tracks.
8.7.3.4.1 The minima set out in 8.7.3.4 shall be applied when:
a) an aircraft is operating directly behind another aircraft at the same altitude or less than 300 m (1 000 ft) below; or
b) both aircraft are using the same runway, or parallel runways separated by less than 760 m (2 500 ft); or
c) an aircraft is crossing behind another aircraft, at the same altitude or less than 300 m
(1 000 ft) below.