What must pilots ensure regarding their flight suit while around aircraft?

Pilots must ensure that all zippers on their flight suit are secured while around aircraft for safety reasons. This practice is crucial because unsecured zippers can catch on equipment, aircraft surfaces, or other items in the vicinity, potentially leading to accidents or injuries. A secure flight suit helps to maintain a professional appearance and ensures that nothing from the suit can become a distraction or safety hazard during flight operations.

While the other options involve aspects of safety and functionality, they do not hold the same level of significance regarding the immediate safety environment around aircraft. For instance, keeping pockets empty can be useful to avoid carrying loose items, but it is not as directly related to preventing incidents as securing zippers. Similarly, ensuring Velcro is attached may help maintain the integrity of the suit but again does not have the same direct impact as ensuring zippers are closed. Prioritizing the fastening of zippers effectively minimizes risks associated with personal attire during critical operations near aircraft.