With extensive monitoring data spanning over 30 years from Vela 5B, Ariel 5, Ginga, Compton Gamma Ray Observatory, Rossi X‐ray Timing Explorer and BeppoSAX, we find evidence for long‐term X‐ray variability on time‐scales
from the black hole low‐mass X‐ray binary system
. Such variability resembles the outburst cycle of Z Cam‐type dwarf novae, in which the standard disc instability model plays a crucial role. If such a model is applicable to
, then the observed variability might be due to the irradiation of an unstable accretion disc. We show that within the framework of the X‐ray irradiation model, when the accretion rate exceeds a critical value,
enters a ‘flat‐topped’ high/soft state, such as seen in 1998, which we suggest corresponds to the ‘standstill’ state of Z Cam systems.