On Fri, 11 Jun 2010 22:25:06 +0100, "Colin McKenzie"
wrote:
On Fri, 11 Jun 2010 17:17:45 +0100, Paul Scott
wrote:
"tim...." wrote in message
...
The third runway ceased to be used in about the late 70s, probably
because it wasn't long enough for modern planes

Not so, it might have been out of regular use but I took off from it in
about 2001 on a flight to Glasgow or Edinburgh, so it was long enough
for a 757. I can date this because my job that required regular flights
to
Scotland was from early 2000 to early 2003.

FSVO modern. If what I was once told about Oslo's old airport (Fornebu) is
true, 757s were able to operate from shorter runways than the Tridents
they replaced. So the 757s may have been one of relatively few jet types
that would fit on Heathrow's short runway, and Tridents may not have been.


The biggest problem with the short runway was that there was no
parallel runway. Not only did take-offs and landings have to use the
one runway, but they had to be in the same direction.

It is normal practice to both take off and land into the wind. This
reduces the length of runway needed, or increases the safety factor.

With the old third runway 05/23, take off had to be into the wind as
it is more safety-critical than landing; if a landing pilot realises
he is landing too fast, or touches down too far along the runway, he
can always take off again and go around. There are no such second
chances for take-offs. ;-)

The fact that 05/23 was only about half the length of the two 09/27
runways was also a very restricting factor:

09L/27R: 3902m x 50m
09R/27L: 3658m x 45m
23: 1962m x 45m

In its final years, 05/23 was only used in one direction in order to
spare the densely populated suburbs of Harlington, Hayes and Greenford
from take-off noise, so it became runway 23. When added to its very
short length, the fact that there was no parallel runway to allow
simultaneous take-offs and landings, and the inadequacy of the
taxiways to serve it properly, this was the final blow for the third
runway and it was taken out of use.

As Paul Scott correctly says, it was some years before this was
officially made permanent.