What aspect of physical condition is not explicitly stated as a requirement for an ATC tower certificate?

The correct choice refers to "physical fitness to operate equipment," which is not explicitly stated as a requirement for obtaining an ATC tower certificate. While it is essential for air traffic controllers to perform their duties effectively and handle the physical demands that come with the job, the specific terminology of "physical fitness" may not be outlined in certification requirements.

In the context of the other options, they all address crucial health and behavioral aspects that could impact an individual's ability to function safely and effectively in the role of an air traffic controller. For example, having no medical issues that impair function is vital to ensure controllers can respond quickly and accurately to changing situations. Furthermore, an ability to perform under pressure is intrinsically linked to the nature of the job, which often requires making critical decisions in high-stress environments. Lastly, a history of substance abuse is a significant concern for any role that involves safety-sensitive functions, like air traffic control, where impairment could have serious consequences. Therefore, while overall fitness might contribute to job performance, it is not an explicit requirement in the same way as the other aspects mentioned.