A major gas works manufacturing town gas was located between the railway and the canal. In 1932 a large gasholder was built which has been a noticeable landmark ever since as it can be easily observed from a long distance away. Painted on the north east side of the gasholder are the large letters 'LH' and an arrow to assist pilots locate Heathrow Airport's (now closed) runway 23 when making visual approaches. The letters were painted in the mid 1960s after a number of pilots became confused between Heathrow and the nearby RAF Northolt (which has a similar, though smaller, gasholder under its approach at Harrow). Northolt has a much shorter runway and is not suitable for very large aircraft although 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 town gas production ceased in the 1970s with the arrival of natural gas piped from the North Sea, much of the site has been vacant, due to limited road access and remaining gas infrastructure.