Parallel runways are NOT necessarily required for simultaneous approaches. At AMS, during inbound peaks, two runways are used for inbound flights, usually this will be a combination of 06 and 01R [with 01L for outbound traffic], or 19R and 27 [24 outbound]. However, exotic combinations like 06 and 27 are also possible for inbound and 01L outbound. This all depends on weather conditions, runway availability, and noise abatement procedures in place.
However these approach patterns are known as "dependent simultaneous approaches", which do NOT require parallel runways. They do require coordination of inbound traffic of both runways. Meaning for example, if an aircraft was approaching for 06, but has to make a go around, it will cross traffic on 01R. So the traffic on 01R is staggered relative to the traffic on 06. These approach patterns are highly efficient: usually AMS can receive up to 35-40 inbounds per runway per hour [plus approx 35-40 outbounds], depending on aircraft mix.
However if you're looking for INDEPENDENT simultaneous approaches [which I guess Arsenal@LHR was getting to], then parallel runways are required. In full IFR conditions, centreline separation of 4300 ft minimum is required. In visual conditions, the minimum is reduced depending on *weather conditions, *surveillance radar available, *ILS category available, *runway lighting, *runway markings etc,etc.
Parallel runways with insufficient centreline spacing can handle dependent parallel approaches. Usually separation between inbound aircraft [for one runway] is 3-3.5 NM. Closely separated parallel runways will allow separation minimum down to 2-2.5 NM, where inbound aircraft are staggered between both runways, resulting in 4-5 NM between every aircraft for each runway.
BTW, this 4-5 NM separation can be sufficient to squeeze in a departure after every landing aircraft, thereby doubling airfield capacity [50% landings, 50% take-offs]! In fact this is about the most efficient use of two runways!
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