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On 8 June, 14:57, Bruce wrote:

Please don't ask any more stupid questions. However, in the unlikely
event that you want to ask an intelligent question, go ahead.- Hide
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I have a question, or several. Why was Heathrow designed like that,
with six runways crossing each other in a sort of Star of David
shape? They obviously wouldn't have been able to use all of them at
the same time, was it intended that they would use two parallel ones
at any one time depending on the direction of the wind? Why were only
three of these runways ever built? When, and why did the third runway
close? What are the numbers and letters at the ends of runways? The
letter always seems to be 'L' or 'R'; the only thing I can think of is
left and right, but that would depend on which direction you were
facing. Is there any significance to the numbers, or are they just
assigned the next free number? EWR seems to have similar numbers to
LGW and LHR, so I assume it must be an international thing.

Slow piston-engined planes are much more affected by wind than jets,
hence the need to have short runways facing in three different
directions. That was the normal layout in the 1940s, when Heathrow was
designed.

All six runways were built, but when jets arrived, three were closed,
leaving space for a much larger central terminal complex. You can still
make out vestiges of the old runways in aerial shots of Heathrow (eg,
one ran under what is now terminal 3's remote pier).

The two east/west runways were lengthened for the jets, which have much
higher take-off and landing speeds. Runway 23 finally closed in 2005,
but was seldom used in the last few years before then. It was only used
when there were strong cross winds. It's now mainly used as a taxiway,
though the southern end is also used for T4 stands.

L and R do indeed mean the left and right-hand parallel runways of a
pair (the few triple parallel runways denote the central one with a C).

The number is the magnetic compass heading. Thus, 27L is also 09R, and
27R is also 09L. These are, of course, east-west runways, which are the
typical direction in the UK because of the prevailing winds (you rarely
see a north-south runway here). The numbers are occasionally revised as
the magnetic compass drifts.