To cater to the rapid growth of road traffic to Heathrow Airport, several rail lines were considered to serve the airport.
An average increment of 1 million passengers a year between 1953 and 1973, and rising issues with airline coach services from major terminals due to location, traffic congestion, larger aircraft capacity and increasing leisure travel further arose the need for public transport connections.
Other than the Piccadilly line extension from Hounslow West, a Southern Railway spur (section now transferred to part of South Western Railway) from Feltham was also contemplated.
These schemes were brought into parliamentary discussion in November 1966, and were approved with the Royal Assent as the London Transport Act 1967 and British Railways Act 1967 respectively on 27 July 1967.
Partial government funding was obtained in April 1972 for the 3.5 mi (5.6 km) Piccadilly line extension, and the estimated cost of construction was £12.3 million.

On 27 April 1971, a construction ceremony was launched by Sir Desmond Plummer, leader of the Greater London Council by bulldozing "the first sod".
Platforms at Hounslow West had to be relocated below-ground to the north of the existing for the new track alignment.
The 1931 ticket hall was retained, with connections to the new platforms.
A new cut-and-cover excavation method was used between Hounslow West and Hatton Cross, a new station on the extension.
This 2-mile section had a shallow trench dug, with the tunnel walls supported by intersecting concrete piles.
The line had to cross River Crane just east of Hatton Cross, therefore it emerges briefly on a bridge, with the two portals having concrete retaining walls.
Deep tube tunnels were bore from Hatton Cross to Heathrow Terminals 2 & 3 (then named Heathrow Central).
On 19 July 1975, the line was extended to Hatton Cross.
The Heathrow Central extension was inaugurated by the Queen around noon on 16 December 1977, with revenue services commencing at 3pm.

In the 1970s, planning was already underway for a fourth terminal for the airport, and its location was to be to the southeast of the existing terminals.
As the Piccadilly line's route to the existing terminals was out of place, a loop track was adopted as the best method to serve the new terminal.
The westbound track between Hatton Cross and Heathrow Central would be retained for emergency services.
Permissions for constructing for the loop was approved and received Royal Assent under the London Transport Act 1981 on 30 October 1981.
On 19 July 1982, the original location of the station and track alignment were altered to compensate for the British Airport Authority (BAA) to finish the fourth terminal building which was behind schedule.
Construction of the 2.5 mi (4.0 km) extension began on 9 February 1983, with an estimated cost of £24.6 million.
The loop was built rapidly, with tunneling completed in 17 months.
It was expected that the extension would open with the new terminal.
However, the terminal opening was delayed, with the loop service completed and commissioned on 4 November 1985.
The terminal and station were finally opened a few months later on 1 April 1986, by the Prince and Princess of Wales.
Regular traffic began 12 days later where trains serve Terminal 4 via a one-way loop, and then Terminals 1,2,3.
The station only has a single platform, and is the only one with this configuration on the Piccadilly line.

The new Terminal 5 would require another extension, funded by BAA.
However, its alignment caused some controversy.
It was reported that London Underground was unhappy of its location on the old Perry Oaks sludge which was originally intended for Terminal 4.
It is now impossible for all 3 terminals to be served on the same route, and the final solution was to have twin tunnels serving Terminal 5 from Terminals 1,2,3.
From 7 January 2005 until 17 September 2006, the loop via Terminal 4 was closed to allow this connection to be built.
Terminals 1,2,3 became a temporary terminus; shuttle buses served Terminal 4 from the Hatton Cross bus station.
Part of the ju
To cater to the rapid growth of road traffic to Heathrow Airport, several rail lines were considered to serve the airport. An average increment of 1 million passengers a year between 1953 and 1973, and rising issues with airline coach services from major terminals due to location, traffic congestion, larger aircraft capacity and increasing leisure travel further arose the need for public transport connections. Other than the Piccadilly line extension from Hounslow West, a Southern Railway spur (section now transferred to part of South Western Railway) from Feltham was also contemplated. These schemes were brought into parliamentary discussion in November 1966, and were approved with the Royal Assent as the London Transport Act 1967 and British Railways Act 1967 respectively on 27 July 1967. Partial government funding was obtained in April 1972 for the 3.5 mi (5.6 km) Piccadilly line extension, and the estimated cost of construction was £12.3 million.
On 27 April 1971, a construction ceremony was launched by Sir Desmond Plummer, leader of the Greater London Council by bulldozing "the first sod". Platforms at Hounslow West had to be relocated below-ground to the north of the existing for the new track alignment. The 1931 ticket hall was retained, with connections to the new platforms. A new cut-and-cover excavation method was used between Hounslow West and Hatton Cross, a new station on the extension. This 2-mile section had a shallow trench dug, with the tunnel walls supported by intersecting concrete piles. The line had to cross River Crane just east of Hatton Cross, therefore it emerges briefly on a bridge, with the two portals having concrete retaining walls. Deep tube tunnels were bore from Hatton Cross to Heathrow Terminals 2 & 3 (then named Heathrow Central). On 19 July 1975, the line was extended to Hatton Cross. The Heathrow Central extension was inaugurated by the Queen around noon on 16 December 1977, with revenue services commencing at 3pm.
In the 1970s, planning was already underway for a fourth terminal for the airport, and its location was to be to the southeast of the existing terminals. As the Piccadilly line's route to the existing terminals was out of place, a loop track was adopted as the best method to serve the new terminal. The westbound track between Hatton Cross and Heathrow Central would be retained for emergency services. Permissions for constructing for the loop was approved and received Royal Assent under the London Transport Act 1981 on 30 October 1981. On 19 July 1982, the original location of the station and track alignment were altered to compensate for the British Airport Authority (BAA) to finish the fourth terminal building which was behind schedule. Construction of the 2.5 mi (4.0 km) extension began on 9 February 1983, with an estimated cost of £24.6 million. The loop was built rapidly, with tunneling completed in 17 months. It was expected that the extension would open with the new terminal. However, the terminal opening was delayed, with the loop service completed and commissioned on 4 November 1985. The terminal and station were finally opened a few months later on 1 April 1986, by the Prince and Princess of Wales. Regular traffic began 12 days later where trains serve Terminal 4 via a one-way loop, and then Terminals 1,2,3. The station only has a single platform, and is the only one with this configuration on the Piccadilly line.
The new Terminal 5 would require another extension, funded by BAA. However, its alignment caused some controversy. It was reported that London Underground was unhappy of its location on the old Perry Oaks sludge which was originally intended for Terminal 4. It is now impossible for all 3 terminals to be served on the same route, and the final solution was to have twin tunnels serving Terminal 5 from Terminals 1,2,3. From 7 January 2005 until 17 September 2006, the loop via Terminal 4 was closed to allow this connection to be built. Terminals 1,2,3 became a temporary terminus; shuttle buses served Terminal 4 from the Hatton Cross bus station. Part of the ju
Piccadilly line