Visual flight rules (VFR) traffic is routinely excluded from capacity models and workload assessments in terminal airspace, despite its potential to increase air traffic controller (ATCO) workload. This exploratory pilot study examined the association between a mixed instrument flight rules (IFR) and VFR terminal scenario and perceived approach-control workload in the simulated Zagreb Terminal Manoeuvring Area (TMA). Nine ATCO trainees completed three within-subject simulator exercises in a fixed order: a mixed IFR/VFR scenario (EXP1), an operationally comparable IFR-only baseline (EXP2), and a higher-density IFR-only scenario (EXP3). Workload was measured using the NASA Task Load Index (NASA-TLX). The mixed scenario was associated with a 9.26-point higher mean weighted NASA-TLX score than the IFR-only baseline (Cohen’s $d_z=0.67$; 95% CI $-1.33$ to $19.85$; two-sided $p=0.079$); an exploratory directional analysis, specified before data collection, yielded one-sided $p=0.039$. The omnibus analysis was not significant ($F(2,16)=2.56$, $p=0.109$). Frustration and Effort were the only subscales with Holm-adjusted p-values below 0.05; these results are interpreted as exploratory. The two IFR-only scenarios showed little observed difference. The fixed scenario order, small trainee sample, and scripted degraded communication preclude causal inference, motivating a larger counterbalanced confirmatory study with operational controllers.