Typical local (z ≈ 0) BH-BH mergers formation scenarios for model M480.B together with the alternative evolution of the same system in models M380.B and M481.B. For all models we begin with the same initial conditions, massive system of 55 M_⊙ primary and 35 M_⊙ secondary on the orbit of 350 R_⊙ and with metallicity Z = 0.0085. In all scenarios, the primary initiates TTMT when it leaves the main sequence and begins to expand in thermal timescale during the HG phase. After 4.8 Myr the primary finishes evolution and explodes as type Ib/Ic SN leaving behind a 11 M_⊙ BH remnant. Next, after the secondary leaves main sequence, due to more restricted condition for CE development, in the cases of model M480.B and 481.B system goes through TTMT instead of CE phase as in standard M380.B model. During TTMT the secondary loses a substantial percentage of its mass (over 60%), together with the system orbital angular momentum. Therefore, the orbit tightens (by a factor of ∼4). After TTMT, in model 480.B, the system remains a BH-He system on the orbit of 150 R_⊙. Due to the high natal kick after the second SN explosion, the orbital eccentricity significantly increases to e = 0.995, which allows the BH-BH system to merge in Hubble time. In standard (M380.B) scenario systems goes through CE phase with HG donor and we assume system a merger (see Sect. 2). In model M481.B due to modified condition for switch between the TTMT and nuclear-timescale stable MT, and the “safety” condition (see Sect. 3.2) after TTMT system also enters the CE phase with the HG donor and merges, leaving behind a single BH. The “He” in the diagram stands for a stripped helium core.