In 2002, IMU121-124 were introduced into service to cope with the extra services needed for the Airport line.
The IMU120s are fitted with electric plug doors as opposed to air operated plug doors on the IMU100s, they are fitted with one A/C pod per car as opposed to two and the cooling system has been changed to water cooling which eliminates the noise associated with the traction blower fans.
| Unit Numbers | 121-124 |
|---|---|
| Introduced | 2002 |
| Gauge | Narrow Gauge (1,067mm or 3' 6") |
| Length when coupled (3-car unit) | 72,422mm |
| Bogie Centres | 17,000mm |
| Bogie Wheelbase | 2,500mm |
| Wheel Diameter | 840mm |
| Width | 2,720mm |
| Height over Roofline | 3,872mm |
| Height of Floor | 1,100mm |
| Speed | 140km/h (87.5mph) |
| Traction Rating | 8 x 180kW |
| Car Designations - Driver Motor Car - Motor Car - Driver Trailer Car | DM M DT |
| Unit Consist | DM-M-DT |
| Tare Weight - DM - M - DT | 46,700kg 47,458kg 37,700kg |
| Seating Capacity - DM - M - DT | 61 82 55 |
| Maximum Acceleration | 0.68m/s² |
| Maximum Service Brake | 1.1m/s² |
| Traction Motor Control | 1 GTO Thyristor converter per 8 asynchronous AC traction motors |
| Transmission | Bogie suspended traction motor through cardan shaft |
| Gear Ratio | 1:4.367 |
| Brake System | Blended regenerative electric and electro pneumatic |
| Auxiliary System | 2 x 100kVA three phase static converters |
| Climate Control | 1 x roof mounted air conditioners per car each with 60kW cooling capacity |