The first units to be built were two prototypes, numbered 4001 and 4002, which were delivered for testing in 1975, and are still in service, these were followed by 88 production units, which were built between 1978 and 1981.
The first units to be built were two prototypes, numbered 4001 and 4002, which were delivered for testing in 1975. After modifications the prototypes joined the regular fleet in service in 1987 and are still in service today, these were followed by 88 production units, which were built between 1978 and 1981.