Ok found it pg.13~14 of the WoW:BD rules
Split-S : -1 Altitude and gets (climb rate -1) climb counters.
Well, not always:
When a Split S is executed, the plane loses a climb counter.
If it has none, it loses 1 altitude level and it takes a number of
climb counters equal to the climb rate of the plane minus one.
Thanks anyway for the answers!