This paper investigates the effects of a 1.5-stage transonic axial compressor with a variable tandem stator arrangement. The experiments were carried out at the transonic research compressor rig at Technical University of Darmstadt. The test rig represents a front stage highpressure compressor of jet engines. Using extensive instrumentation, the global performance is analyzed. A new designed compressor stage has been commissioned, including a BLISK rotor and tandem stator vanes with variable stagger angles. In comparison with a reference stage using a conventional stator design, the new stator design enables a higher aerodynamic stator vane loading. Therefore an optimized stage loading is pursued, leading to an increased work coefficient whilst retaining the operating range of the stage. The experimental study reveals several effects of the optimized compressor stage, considering both, performance and corresponding aerodynamics. The operating range with varying VIGV-VSV schedules differs to the reference case. At nominal tandem stator vane closure, stage pressure rise is increased for the whole operating range. Comparing the stage exit aerodynamics of the tandem and reference stator at design speed, distinct differences appear. In conclusion, the conducted experimental investigations prove potential capabilities of transonic compressors, enabling optimized stage loading.