FPOBN,
There is either the requirement to separate due to wake, or not. Two Lower Medium category aircraft, such as B737s, do not require any wake turbulence separation, just as a pair of Cessna 150s do not require any wake turbulence separation.
Hence why we have a 2.5nm spacing procedure at LHR where, for non-wake pairs, providing Tower can apply visual separation when the first aircraft reaches 4DME, separation is 2.5nm delivered to 4DME, which can compress to even less than 2nm as the first aircraft touches down.
RECAT1A, where it mentions MRS, does not mean that 2.5nm is the wake turbulence spacing, just that this is the closest aircraft are permitted under radar separation on final approach. If aircraft pairs where "MRS" is specified are being separated visually, there is no radar separation requirement. Would you really expect an A380 to have to have 2.5nm wake turbulence spacing behind a E120? The table even explains that it could be 3nm, and implies that it could be greater....some areas in the UK MRS is 5nm. As this figure varies, it demonstrates that MRS is not a factor in wake separation.
Last edited by Gonzo; 19th Dec 2012 at 21:07.