Aircraft maintenance unit

The disclosure relates to a maintenance unit for servicing aircraft during stand-still, comprising electrically powered service and/or maintenance equipment. There is a power input for connecting the unit to an electrical power supply operating at 200/115VAC at 400 Hz. The unit further comprises a transformer and conversion unit (TCU) for transforming the 200/115 VAC/400 Hz power to standard grid voltage at 400/230VAC at 50 Hz and at least one frequency converter enabling variable frequency of the output voltage, for powering said service and/or maintenance equipment. The maintenance equipment may be a gas turbine engine washing equipment and comprises a water delivery member for supplying water from a water source, a high pressure pump coupled to the water providing means for providing pressurized water, and a high pressure water outlet.