A major gas works manufacturing town gas was between the railway and the canal. In 1932 a large gasholder was built which has been a landmark from far away. Painted on the north east side of the gasholder are large letters 'LH' and an arrow to assist pilots toward Heathrow Airport's (closed) runway "23" when making visual approaches. The letters were painted in the mid 1960s after a fraction of pilots at a glance mistook RAF Northolt (which has a smaller gasholder under its approach at Harrow). Northolt has a much shorter runway and is not suitable for very large aircraft; one Boeing 707 did land at Northolt by mistake and a number of other aircraft had to be warned off by air traffic control at the last minute. Since such gas production ceased in the 1970s upon tapping natural gas piped from the North Sea, much of the site has been vacant, due to limited road access and remaining gas infrastructure.