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|Locale||Kuala Lumpur International Airport, Malaysia|
|Owner||Malaysia Airports Holdings Berhad|
|Operator(s)||Engineering Transportation, Malaysia Airport (Sepang) Sdn. Bhd.|
|Character||Serves sterile parts of the airport|
|Rolling stock||3-car 2 trainsets of Bombardier Innovia APM 100|
|Track length||1.2 km (0.75 mi)|
|Operating speed||Maximum speed 56.3 km/h (35 mph), Minimum speed 46.7 km/h (29 mph)|
|Highest elevation||Partially underground|
Opened in 1998 along with the airport, the Aerotrain system consists of two stations, one in the Main Terminal Building and the other in Satellite Building A. The system is the only means of transport for passengers between the two terminals.
Upgrading works on the Aerotrain had caused the service to be suspended between November 1, 2010 and March 15, 2011. Passengers were transferred between the Main Terminal Building and the Satellite Building by bus shuttles during the upgrading period.
The Aerotrain is fully automated and driverless. Usually, two trains ply between the two stations. In accordance with the Spanish solution, when the train reaches the platform, the exit doors will open first for passengers to disembark, after which the entrance door on the other side will open.
Part of the train track goes underground to cross the taxiway. The ride between the Main Terminal Building and Satellite Terminal A takes about 2.5 minutes.
The Aerotrain supported various operating modes such as Synchronized Double Shuttle Mode, Offset synchronized Double Shuttle Mode, Unsynchronized Double Shuttle Mode, Single Shuttle Mode, On-Call Mode, Test Train Mode and lastly Out Of Service Mode. The Aerotrain has 4 major sub-systems which is the Central Control System, Vehicle System, Station Automatic Train Operation (ATO) System and Power Distribution System (PDS). The trains have an operating speed of 56 km/h with a 3-phase 600 V power supply at 50 Hz. A 100 hp DC Electric Motor constitutes the propulsion system of the trains.
The maintenance of the Aerotrain is scheduled at 1000hrs till 1200hrs and 0000hrs till 0500hrs everyday. During those periods, only one of the trains will be running for operation and the other one will undergo maintenance works and safety checks. The frequency of the train decreases from every 2.5 minutes to every 5 minutes during the maintenance periods.
The rolling stock is manufactured by Adtranz (acquired by Bombardier Transportation). It comprises three Innovia APM 100 trains with three cars per train (originally two cars), of which each car has a capacity of 249.
On March 15, 2011, a new train has been added to the fleet which is known as Train 3. The addition is made to cover the shortfall of the Aerotrain system when either Train 1 or Train 2 is scheduled for an overhaul programme. The overhaul programme is necessary as both Train 1 and Train 2 has been in use for 13 years.
On 25 December 2017, one of the trains broke down in between the two terminals and a detrainment was carried out. This left the aerotrain running on a single train and free shuttle buses were provided.