NMBS/SNCB Classical twin EMUs (also referred by their construction year - AM50 for "Automotrice 1950" up to AM79 for the last units from 1979) (or MS50 to MS79 for the Dutch-language equivalent "Motorstel") are electric multiple unit trains operated by the National Railway Company of Belgium (NMBS/SNCB). They were the standard equipment for local trains under the Belgian standard 3000 Volts DC overhead lines, until gradually replaced by the Class 08 Desiro Mainline EMU's starting from the early 21st century.

NMBS/SNCB Classical twin EMUs
NMBS/SNCB EMU AM 174 in Liège Guillemins Station
2nd class original interior
In service	1939–present
Manufacturer	La Brugeoise et Nivelles / ACEC
Constructed	1939–1979
Number built	497 (not in service at the same time)
Formation	EMC-EMS
Capacity	118 to 185, depending on series
Operators	NMBS/SNCB
Specifications
Train length	44.4 m (145 ft 8 in) to 46.575 m (152 ft 9+5⁄8 in), depending on series
Width	2.781 m (9 ft 1 in) to 3.000 m (9 ft 10 in), depending on series
Height	3.767 m (12 ft 4 in) to 4.400 m (14 ft 5 in), depending on series
Doors	AM39: Sliding doors Rest: Pneumatic folding doors 4 per side (excl. baggage door)
Maximum speed	130 km/h (81 mph)<b→r/> 140 km/h (87 mph) AM46 + AM66 and up
Weight	98.5 t (96.94 long tons; 108.58 short tons) to 117 t (115.15 long tons; 128.97 short tons), depending on series
Power output	620 to 840 kW (830 to 1,130 hp), depending on series
Electric system(s)	3000 V DC 1500 V DC (Netherlands) Catenary
Current collector(s)	Pantograph
UIC classification	(A1)(1A) + (A1)(1A)
Safety system(s)	TBL1+ (units 642 and up)
Coupling system	Henricot semi automatic coupler
Multiple working	Within class (all series are interoperable) and with AM75
Track gauge	1,435 mm (4 ft 8+1⁄2 in) standard gauge

Classical EMUs were originally painted in dark green, with small yellow stripes surrounding the front lights. As those were considered insufficiently visible, the front door was also painted in yellow and the stripes were enlarged.

A subset of 22 EMUs was built with stainless steel body instead of (regular) carbon steel. This remains a one shot trial as the next generations were built with carbon steel bodies.

Another subset of 6 EMUs were specifically adapted for airport service, with more space between seats and a huge luggage compartment. Although they were operated by railways staff, access was restricted to Belgian airlines travellers with a dedicated platform at Brussels Central Station. A blue paint scheme was also chosen to identify those EMUs.

In 1984, the Belgian Railways introduced a new transportation plan based on fixed-interval timetables (and the closure of many secondary passenger lines) called "Plan IC-IR." A new paint scheme was applied, based on a burgundy red color with a large white line surrounding the entire coaches or EMUs below the windows.

In 1999, classical EMUs built in the seventies were extensively refurbished, the program included comfort upgrade (interior replacement, sound system, closed circuit toilets) and repainting in the light gray livery with blue and red lines under the windows. Few units were still in the older green delivery when refurbished. The last 40 to be refurbished units received extra features (LED information displays, multi-service compartments for bicycles or standing passengers) for suburban "CityRail" service.

In 2013, a hundred non-refurbished units were scrapped, after many of the Desiro Mainline Class 08 entered into revenue service.^{[citation needed]}