Objective We examined whether active head aiming with a Helmet Mounted Display (HMD) can draw the pilot’s attention away from a primary flight task. Furthermore, we examined whether visual clutter increases this effect. Background Head up display symbology can result in attentional tunneling, and clutter makes it difficult to identify objects. Method Eighteen military pilots had to simultaneously perform an attitude control task while flying in clouds and a head aiming task in a fixed-base flight simulator. The former consisted of manual compensation for roll disturbances of the aircraft, while the latter consisted of keeping a moving visual target inside a small or large head-referenced circle. A “no head aiming” condition served as a baseline. Furthermore, all conditions were performed with or without visual clutter. Results Head aiming led to deterioration of the attitude control task performance and an increase of the amount of roll-reversal errors (RREs). This was even the case when head aiming required minimal effort. Head aiming accuracy was significantly lower when the roll disturbances in the attitude control task were large compared to when they were small. Visual clutter had no effect on both tasks. Conclusion We suggest that active head aiming of HMD symbology can cause attentional tunneling, as expressed by an increased number of RREs and less accuracy on a simultaneously performed attitude control task. Application This study improves our understanding in the perceptual and cognitive effects of (military) HMDs, and has implications for operational use and possibly (re)design of HMDs.