I watched the PanAm 707 land at Northolt by mistake (lined up with the South Harrow gasometer rather than the one in Southall) all those years ago from the school playground. The power that be resorted to twenty feet "NO" for the Northolt and "LH" for Heathrow lettering on the associated gasometers!
Years later landed many times on 23(L) at Heathrow, even landing on 23R in the days when Heathrow had six runways!
I also remember the Trident Groundspeed showing 60kts as we passed over the Southall gasometer during the '87 gale.
Sadly passing through Southall on the "Great Western" yesterday it looked as if the gasometer was in it's death throes, should have been "listed" as a reminder of the part it played in Heathrow's history! (It's sister at South Harrow having been demolished years ago)!
Southall Gasholders
Time marches on...