FLASH is DESY's free-electron laser user facility providing ultra-short femtosecond laser pulses in the EUV and soft-X ray wavelength.FLASH is also a pilot facility for the European XFEL project and a test bed for further research and development for linear collider related superconducting accelerator technologies. Since 2014 the FLASH Linac operates two seperate beamlines, FLASH 1 and FLASH 2, in parallel. Currently a third beamline, FLASHforward, is under construction and installation. To keep the accelerator running and to provide time for installation work regularly maintenance and shutdown periods are needed. On behalf of the whole FLASH Coordination team, we describe the organization, the work flow of those periods and the hence resulting difficulties and pending issues.