What is the most serious category of runway incursion?

The most serious category of runway incursion is Category A. This classification indicates a serious incident in which a collision was imminent or had the potential to occur. In these cases, there is often inadequate separation between aircraft and any vehicles or personnel on the runway, leading to a highly dangerous situation. Category A incursions typically involve significant risk to safety and can occur due to various factors, such as miscommunications, errors in judgment, or lack of situational awareness by pilots or ground personnel. Understanding the categories of runway incursions is crucial in maintaining safety at airports and preventing accidents.